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The following are some various notes I've accumulated on Product Management. Enjoy!ResponsibilitiesProduct Manager is accountable for the overall success or failure of the products. This includes not only envisioning how your product will be successful today but how it will continue to grow revenue, profitability and market share over time.- maintain a prioritized list of market requirements that continually improve your products’ performance and the financial return to your organization- manage a rolling tactical roadmap that outlines what customers can expect from your going forward- lead cross-functional collaboration efforts across the organization in support of product objectives- interact externally with customers, prospects, analysts and business partners which include focus groups advisory committees surveys or customer visits- provide training and support to internal stakeholders who interact with the customers that use your products- establish and communicate performance metrics for your products and report progress versus plan- allocate most of your time to the 20 percent of activities that drive the highest probability of your organization’s success- execute a 3-5 yr vision and a shorter term tactical execution plan that covers a rolling 12 months- to balance competing priorities ask 2 key questions: does this help us attain the company’s product objectives more quickly? will supporting this request enable you to become more efficient by reducing future or redundant requests for your time?- Apply your time first to those things that help you attain your objectives or make you more efficient by reducing future demands on your time- Central mission of product managers is to know their markets, customers’ needs, competitors, and trends better than anyone else. Objective is to collect information from a variety of sources and focus on what is most important based upon the best data and facts available.Draw an influence map that visualizes people who will be the most important contributors to your product’s success and get access to a copy of the business plan or at least the sections that pertain to your dutyFigure out what the company is trying to accomplish with its product activities: creating new value through innovation or augmenting existing valueStartups focus on creating new value through innovation - a high degree of flexibility is required to succeed as your assumptions about the market and customer needs are continually challenged. Lots of facetime with clients and development team and a lack of detailed processes. Skills needed at this stage are:Creative thinkingEntrepreneurial SpiritConceptual and analytic abilitiesMidsized companies focus a significant amount of resources on augmenting their existing products to ensure continued high rates of growth - company is tapping into mass market and bringing along early adopters that initially made it successful. Customers are looking for complete products with all the bells and whistles AS WELL as a product roadmap. Skills needed at this stage are:StrategicProcess developmentCross-functional engagementAnticipating problemsCalm under pressureLeadershipBudgetingMature companies require both augmenting and innovation skills. Innovation is necessary to achieve ever growing revenue targets via partnerships, or M&A. Skills required are:StrategicLeadershipPolitical astutenessAnalyticHighly developed interpersonal skillsCross-functional abilitiesProfit and lossCalm under pressureThree Product Management ApproachesCapturing the voice of the customer - what customers tell you they want.Allows you to capitalize on readily available sources of info, many of which reside inside the organization.Enables you to augment existing product and preserve existing prod. dev. momentum while you gather necessary market info with which to make informed decisions about product’s future direction.Good for augmenting existing products. NOT well suited for developing new innovations given its reliance on explicit needs.Establish process to capture customer inputs from variety of sources, ranging from 1on1 convos to customer queries.Establish framework for prioritizing various inputsEnsure proactive collection and a continuous feed into a product decision framework for evaluationFollowing these methods will quickly point to ways that your existing product line can be augmentedDecision frameworks provide logical rationale for explaining why you decide to invest in one product enhancement over anotherWorkflow Analysis - What you observe about how customers do their job.Allows you to gain deep insight into how your customers and prospects accomplish their work and correctly identify the problems they deal with so you can provide solutions.Allows you to identify common business problems shared by a broad set of customers and prospects, which provide insight into larger market opps. to reduce inefficiencies, save time, save money and increase the satisfaction of those performing tasks as part of the business process.Allows you to be embedded in your company’s processes, resulting in a codependent relationshipUltimately this allows you to transform the way your customers accomplish their objectives and make your marketing and sales processes more effectiveGood for both identifying opps. to augment or creating new value through innov.Approach customers with a clear and compelling value prop, with a promise that your insights will generate a significant return that both parties can benefit from as these steps require a significant amount of cust. engagement and time.Spend time with customers and capture steps that are taken to achieve a desired outcome, the people involved and their interactionsDocument each step of a customer’s workflow - the interactions between people in a process, their productivity and output, to establish a baseline.Outcome-driven approach - Understanding what customers are trying to achieve as they do their jobs and the metrics used to define success. It postulates that once you know what jobs and outcomes cust. are trying to accomplish, you’ll be able to methodically create products and services that generate valueAllows you to determine which performance metrics matterAllows you to reduce variation in the success or failure of value creation activities by offering a means to fully understand customer success metrics upfront BEFORE any investment in developing or extending a product.Allows you to target areas that give you the best chance of enabling cust. success without wasting resourcesGood for augmenting existing prod. and creating new value through innov.Determine where you need to focus: end user, buyer, partner or someone else? Who in the value chain makes the most important judgments about value and the metrics used to define success?Capture the measures of value that define how customers want to get the job done: the process steps taken, outcomes they are striving to achieve, definition of what it means to do the job perfectly, and the constraints that stand in a way of successfully completing the job.To collect this info, conduct a series of customer interviews from a statistically significant sample of the client baseScore the collected data and chart them on a graph that shows areas of opportunity that reveal 3 categories of needs:Underserved - opp. for growthOverserved - opp. for ceasing investment. cost reduction or potentially disruptive innovationAppropriately servedTurn a blind eye explicit customer statements that don’t conform to the process you’re followingCustomer ResearchMarket Research - used to investigate new business opportunities, identify causes of problems and provide additional information to aid in making an important decisionsMarket information - size of market, how its segmented or current trendsMarket structure - identifying the major players and their market share, brand market share or market’s distribution structureBuyer perceptions - buyer needs’ assessment or perceptions of various brands and suppliersProduct - analysis of the available products, usage and consumption patterns, differentiation, segments served or satisfaction levelsNew Prod. Dev. - defining unsatisfied needs, product acceptance or communicationPricing - sensitivity, trends, or mapping existing pricing structuresCustomer satisfaction surveyCustomer list - acquire a descending dollar volume list of active customers from finance department. If list includes inactive clients than ever better.Look for patterns in active customer listWhat do top 20% of customers have in common?How far reaching are your products in terms of geography?Does the list contain resellers of products or end users?Look for patterns in inactive customer listWhy did they stop?Any common characteristics?Identify thought-leading and valued customers who will help you enhance your product and plan to meet them once readyCollect presentations and collateral - collect the most current sample of your cust.-facing presentations from each functional area currently in use across your organization (brochures, PR, publications, articles, advertising, product fact sheets, white papers, case studies, webinars etc.)Is the product(s) consistently portrayed?Do they discuss future dev. activities? if so, what is promised?Does the sales support materialWin/Loss Analysis DataAllows you to gain current understanding of how new customer or prospects perceive the product and organizationAllows the sales team to identify ways they can improve executionStart by reaching out to unsuccessful sales prospects or newly acquired client and ask a series of questions:What companies were involved in selection process?How did we stack up?What are our perceived str and weaknessesWhat factors led to our victory or loss?Can you overview the decision-making process? who was involved and what were the key selection criteria?What could we have done diff. to improve?Customer Agreements and Signed ContractsAsk for recently signed customer agreementsAnalyze patterns and any changes that emergedAvailable Competitive InformationRequest competitive information available ‘in the public domain’.This Allows you to develop a superior market position by understanding customer needs better than anyone elseIdentify Internal Customer Data SourcesInvestigate where databases of customer information are being kept within your organizationLook in incoming customer support calls, online client discussions groups, fan page interactions, info related to lead generation, trade shows, conferences etc.Defect or “bug” reportsMany of these defects are identified during QC processOthers make it past QC and are identified by customersOnce a defect is confirmed, a priority rating is assigned to the problem using the following framework: critical issue, high priority, medium priority and low priority.Ask engineering team for defect reportsProduct Cost or Profit and Loss InformationAcquire a product P&L statement IF there is oneAsk Finance to walk you through it to make sure you fully understandThis allows you to determine if your product(s) are profitableExisting Product-Related MaterialsProduct roadmaps, visioning documentation, product-level business cases, product launch materials etc.External info sourcesAnalyst ReportsSocial mediaBusiness IntelligenceSurvey your internal constituentsWhat do you see as the biggest opps. and challenges in next 2 months to a year? 2-5 yrs?Do you believe we have clear prod. vision? is it clearly communicated throughout the org?Does our prod. roadmap enable achievement of our vision and plan?Are we on track?Is prod. management appropriately aligned with other functions?3 yr product visionbounce off ideas with thought leaders in your org. and then clientsThink of a 3 yr vision and begin with end in mind. Highlight what will happen at end of year; mid-point and end of 3 yearsList strategic product milestones in a ‘vision slide’ along with key deliverablesProduct MilestonesCall thought leaders together and facilitate a brainstorming session to capture their views of the marketBefore meeting, send every attendee explanation of meeting objective and copy of product vision MARKED DRAFTDuring meeting, capture all comments in bullets on the slideKeep everyone involved although a few will dominateStart from discussion of current state, jump to end and then goto middleAfter the meeting review the ideas and follow up with those who provided itPull out customer list and reach out to key customers and prospectsDiscuss with sales people and thought leaders in org. who the key customers areSetup meetings, preferably in person and take the sales person alongDuring meetingExplain objectives and ask the client where they believe the market is headedHave them describe the top 3 challenges they are facing today and how they are handling them.Explain to them you are finalizing thoughts regarding future direction of product and that you’ve developed a plan that you want to get their feedback on.Post-meeting assess customer’s reaction and see if the vision addressed any of the top 3 challenges the customers told you aboutFurther define each concept for the vision slidePull together several short paragraphs that describe the substance behind the concept; flesh out each conceptual milestone that will enable everyone in your org. to receive the same message and help you manage client expectationsThe presentation slide detailing each milestone contains:Title of milestoneDescriptionCustomer value prop.Operational considerationsDate slide was createdHave 1 slide per milestone and create short paragraphs that describe the substance behind the conceptual milestone. i.e. FOR “public accountability” milestone, write: Public accountability reporting will provide relevant executive level summary information and trends at a glance in real time to support governance and public reporting mandates.Next construct the value prop outlining why your cust. should be interested in the capability you’re planning to bring to market. i.e. Alpha Tech Ventures’ real-time public reporting capability will enable executives to review and effectively comply with mission-critical governance and public reporting mandates and reduce the risk of incurring a legal liability by 50 percentFinish with operational considerationsCreate a Solid Business Case - cost benefit analysis justifying investment. Business case details the various benefits, costs, and risks of pursuing a suggested course of action and supports the request for a budget to enable the effort to proceed. This allows you to align executive leadership team behind your product vision, build momentum, enlist support from diff. components, and align thought leaders, key customers and prospects behind your vision.Executive summaryConsolidation of most important info that enables a busy exec. to understand at a glance (1-3 pages)Should be the last section you writeProblem or opportunity statementProvides the necessary context to understand your request for additional resources.Needs to be aligned with company’s overall business strategyDescribe what is happening today that provides an opportunity to capitalize on (i.e. if you identified new market niches that are underserved or a means to improve your product’s market performance by adding services)Solution overviewHigh-level description of desired outcomeExplanation how your proposed sol’n addresses the market opp. or problem that you’ve highlightedRange of alternatives consideredDescribe why you’ve selected preferred option, demonstrating you’ve considered all available options to sol’n you’re proposingCost estimatesOutline total projected costs and future financial return on investmentCosts include prod. dev costs, FTEs, QA/testing, maintenance etc.Benefit analysisOutline benefits with the goal to compare estimated costs with benefitsProjected financial returns need to exceed anticipated costs and hurdlesMention all benefits: incr. market share, cust. satisfaction, decr. employee turnover etc.Implementation timetableState key milestones and how long it will take to bring new capabilities to marketIdentify what resources will be required to make this happen.Critical assumptions and risksConclusion and final recommendationsSummarize key themes and benefits and anticipated financial returnsProduct Lifecycle Management (PLM) Framework - guides products from an idea to ultimate retirement, going through 4 distinct stages (introduction, growth, maturity and eventual decline). PLM integrates cross-functional product activities - information, people, and processes throughout the product lifecycle with the aim of increasing efficiency and reducing execution risk.This allows each participant to understand the overall process, their role and expectations.This allows the company to create standardized deliverables that other parties involved in the process are counting on to do their jobs7 Phases of product lifecycle - each has defined activities, owners, collaborators and a descr. of expected deliverables at each stepStrategyRequirementsAnalysis / DesignDevelopmentDeploymentOperationRetirement12 diff activities that take place over the course of a product’s life - and each has defined owners, collaborators and descr.Strategy (development)Business case (justification)RoadmapRequirementsPlanAnalysisDesignBuildTestDeployOperateRetireDetermine who owns the PLM process. If none exist, then collaborate with key participants to define the PLM process for your org.Developing requirements - gathering inputsDetermine which product management methodology to useIdentify which sources you will use to collect inputs fromCollect relevant inputs into a central repository and convert the data into a useful formCreate a rational framework for evaluating and turning centralized inputs into prioritized requirements (Product Decision Matrix)Begin by drafting the metrics you intend to use to filter the inputsPresent draft to senior leadership team for buy-inExplain to everyone involved, and the requirements that rise to the top become the foundation of your product roadmap.Once you create your own product decision matrix, you end up with a prioritized list of high-level requirements in descending importance that list opp. your org. has to create value for customers.Form a standing cross-functional team of members from various areas to look at each prioritized requirement from an operational perspective and identify potential issues before they happenSelect people knowledgeable about the product and good team contributors with influence over their counterpartsHave a range of divergent perspectives (not just yes people) and preferably those in the same room as youList possible candidates (2 from each functional area)Explain mission of the group and decide on first meeting date as well as frequencyYou now have a req. list vetted by cross-functional counterparts for operational feasibilityDeveloping Product Roadmaps - operational plan that highlights your products’ quarterly development activity over a rolling 12 months. Most companies have 1 roadmap per product or family of related products. It’s best to create 2 types of product roadmaps: internal and externalRelease - planned deliverable that is slotted into a calendar quarter over the course of the annual plan.Items placed in roadmap provide high-level descr. of each release (not intended to communicate detailed scope or cost)Releases fall into 1 of 3 categories and you must balance these to sustain market growthNew Value Creation - release of a new product, component, capability or feature that gives customers increased value.Maintenance and Support Releases - updates to existing cust-facing products that preserve product’s revenue stream. This does not create new value but enables cust. to continue to extract expected value from productInternal Product Releases - investments made in the components of your offerings that aren’t seen by customers. These help daily ops.Internal use - roadmaps are used to coordinate cross-functional activities in support of a release, manage expectations of internal constituents, drive accountability and measure product dev. team’s productivity and performance (scope, cost and schedule)Your company’s staff must be trained on new products’ capabilities to support client inquiriesMarketing must be prepared to get the message outSales must be ready to communicate value of release to clientsExternal use - used to manage client expectations and as part of the sales processProduct Development - execution phaseAlign incentives by drafting shared performance-based objectives between different functional groups and improve coordination.This allows the company to achieve their desired goals by linking them to compensationEngineering and product management team need to accurately estimate the time and resources needed to create a given requirement.Product management must communicate clearly about the scope of what is to be accomplished based on previous prioritizing efforts; this involves relating priorities back to the business value they are attempting to createRevise the cross-functional meeting structureHold coordinated meetings at standard intervals (at their end) in the PLM process:Strategy - Objective is for prod. manag. to propose the new prod. capabilities to internal cross-functional prod. dev teamReq. - Objective is to establish a final set of expectations that clearly demo. that the commercial success criteria can be metObjective is to focus on the proposed design of prod. or capabilitiy and seek approval from biz owner and buy-in from extended cross-fxnal team members who would support the prod. post-dev.Development - Obj. is to be sure that your prod. is ready to launch, with testing and refinement complete and sign-off from biz owner and cross-fxnal dev. team.Include the business owner and internal cross-functional team members involved in prod. dev.This allows you to make sure that there is a business owner review with the extended team to agree to the plan, mitigate risks and improve overall coordinationFurther Defining Requirements - Various sections of the requirement document. It’s important to maintain flexibility and to indicate that any plans are subject to change based on market conditions (markets, competitors, M&A etc.)About this documenthistory of the doc (date, version, who made changes, descr.)descr. of key termsBusiness analysisDescribe business need at a high level and highlight key business questions the new capability is attempting to addressProposed release date tied to product roadmapList high-level biz/market req., with associated descriptions, If necessary insert SWOT and any underlying assumptionsFeature Matrix - prod. dev. estimates for prioritized list of features. Goal of this is to provide a ‘cut off-line for prod. dev. based upon available time, resources and moneyHigh-level use casesUse cases capture detailed biz req. which are then turned into fxnal specs for your productCreate a diagram illustrating the system that the user is interactingw ith to receive value from the new capabilities you’re developingList an actor heirarchy if more than 1 party is using product and list all use cases that have been developedFunctional req.These are the specific elements that define what a product is supposed to accomplish and are used to the guide the design of the productThese roll up into a use case - into the behavioral elements of how the product will be usedCompliacne req.Regulatory compliance refers to any rules, regulations and req. that re relevant to meeting a governing body’s laws or mandated procedures.These might include data use rules, security, contractual requirements, governmental obligations etc.Report req.Inputs, layout, report fields, headers and footers and any groupingsUI req.Begin with a conceptual site map and detail the associated navigationOften presented in a diagram detailing the analysis that has been conductedEnvironment req.This often includes architecture standards relating to system performance and any environment considerations as well as operational and integration requirementsIterating with customersinteract with customers as much as possibleTake a structured approached with your customers that lets them know that you value their timeStart by defining an objective.. what are you hoping to accomplish?Assess how much time they have by asking them upfront.Pick an appropriate forumSite visitsSurveysVirtual meetingsVisits to your corporate locationRegional client meetingsClient conferencesFocus groupsCreate a frameworkWalk them through product visionReveal your roadmap quarter by quarterDemo a prototypeExplain various pricing scenariosSend a thank you noteCustomer Advisory CouncilsAllows you to put a structured client input process in place to aid your product activities by ensuring thoughtful customer input into strategic or tactical product matters.Typically comprised of 7-9 clients who possess a keen insight into your market or the use of your productAsk yourself what roles do you intend to include in your council? hands-on users or economic buyer who may not be the hands-on user?Geographic distribution - its better to have those in the same room as youAdvisory council charter should cover the following topicsObjective of the groupFrequency of meetingsMeeting durationMeeting locationParticipants in the councilTimeframeMeeting dates and topicsOther expectationsExpensesPoint personSupporting the Product LaunchLaunch stylesLaunching your product into an existing marketExisting markets typically have a # of dominant competitors all jockeying for market shareRequires you to have a distinct value prop that lets you stand outLaunch plan needs to single-mindedly focus on acquiring new customers and creating demand for your productLaunch plan relies on ‘all in’ approach using every available demand creation tool at your disposal to gain maximum attention over a specific timeframeLaunching your product in a new marketPrepare to invest for the long term with the objective of driving awareness and ultimately adoption of your productTarget early adopters to establish momentum and spark interest of a currently uncaring mass market by educating themResegmenting an existing marketThis effort focuses on carving out a piece of an existing market by offering a lower-priced product than your competitors or by targeting a segment of the market that plays to your product or services strengthsObjective is to both educate and capture market shareIf market is ready to buy then consider the “all in” approach; if not focus on attracting early adoptersCreate a product brief on the product or capability you’re launchingOutlines the critical information regarding your value prop., customer audience you’re targeting and the key messages and channels you’re use to get your message outContent will be created once and used many timesThis allows your executive team to see your thought process and value prop. before the launch.Marketing will use the structured content you provide to professionally craft the message in their marketing plan and sales support materials as well as select the right channelsIt contains the following information:Product name and release dateWho the product is targeted toDescr. of the product or capabilitySummary of the key customer business needs that the prod. or capability will addressCustomer value prop.Client impactDescr. of the launch plan and timing of key eventsBenefits and featuresSales and cust. service talking pointsPricingResources and additional info.Create a launch plan frameworkEstablish your launch date and work back from thereList the activities that need to take place before that date to determine when your plan needs to startCreate a calendar that includes dates and breaks time down into weekly increments over that timeCreate columns to list the activity, owner, deliverable, target and source of needed material in chronological sequenceMarket Dynamics and Competitive Analysis FrameworksPoint-in-time Analysis: Market view analysis generally consists of the following. Place each in 1 slide.Market focus - Frames the specific market that your company is targeting and sets the context for other aspects of the analysis (i.e. BI software sol’n for U.S. hospitals)Market Size and anticipated Growth Rate - (i.e Detail how the segment targeted fits inside the overall U.S. healthcare market)Current Company Market Position Overview - Market leader? contender or further back in the pack? List company’s market share and detail where company fits into context of competing companies all vying for a piece of the BI sol’ns market)Market Segments Description (i.e. BI sol’ns for hospital finance, clinical decision support, and client satisfaction)Top Competitors Matrix, segmented by market - describe how competitors compete with organization. Do they only impact 1 market segment or multiple? List competitors on left and have series of columns that show revenue and market segments they play inDetailed Competitor Breakdown -Prepare short narrative describing each top competitor’s profile, strategic direction and partnerships.The profile paragraph should outline each company’s primary focus and what differentiates their market approach from competitors.Strategic direction segment should outline known strategy and where you think the company is headedCurrent Position Overview - Describe company’s core capabilities. Ask, what are the core gaps that need to be filled? What segment-level opps. exist that can be capitalized on?Buy-vs-Build Opportunities - Outline each gap that needs focus and the str and weakness of the current position. Also frame whether it’d be better to buy or build certain aspect of products’ future capabilitiesPossible Acquisition Candidates - detail possible targets over short and long-term to shore up competitive position. List target companies, revenue and market segment they serveList of Risks and Contingencies - detail risks with buy recommendations.Is it clear how target company should be valued?Spell out contingency plans. What happens if preferred target is not open to being acquired? what is next step? will organic dev. be pursued or other acq. targets be looked at?Potential Competitive MovementsHave competitors been on acq. binge lately?Have they raised capital?Are they trying to control strategic channels important to business?Deep Dives into Specific Competitors - Create a quick summary of each competitor, annual revenue, # of employees, ownership status, products and any conclusion that has been reached.Narrative Competitive Analysis: Customer-facing frameworkName of competitorOrg. historyBusiness model and revenuesMissionVisionStrategyEstimated client levelsPartnershipsPositioningDetailed analysis of product/service offering and stated benefitsPricingRecent developments

An assertion is a statement in the Java programming language that enables you to test your assumptions about your program. For example, if you write a method that calculates the speed of a particle, you might assert that the calculated speed is less than the speed of light.Each assertion contains a boolean expression that you believe will be true when the assertion executes. If it is not true, the system will throw an error. By verifying that the boolean expression is indeed true, the assertion confirms your assumptions about the behavior of your program, increasing your confidence that the program is free of errors.Experience has shown that writing assertions while programming is one of the quickest and most effective ways to detect and correct bugs. As an added benefit, assertions serve to document the inner workings of your program, enhancing maintainability.The assertion statement has two forms. The first, simpler form is:assert Expression1 ;where Expression1 is a boolean expression. When the system runs the assertion, it evaluates Expression1 and if it is false throws an AssertionErrorwith no detail message.The second form of the assertion statement is:assert Expression1 : Expression2 ;where:Expression1 is a boolean expression.Expression2 is an expression that has a value. (It cannot be an invocation of a method that is declared void.)Use this version of the assert statement to provide a detail message for the AssertionError. The system passes the value of Expression2 to the appropriate AssertionError constructor, which uses the string representation of the value as the error's detail message.The purpose of the detail message is to capture and communicate the details of the assertion failure. The message should allow you to diagnose and ultimately fix the error that led the assertion to fail. Note that the detail message is not a user-level error message, so it is generally unnecessary to make these messages understandable in isolation, or to internationalize them. The detail message is meant to be interpreted in the context of a full stack trace, in conjunction with the source code containing the failed assertion.Like all uncaught exceptions, assertion failures are generally labeled in the stack trace with the file and line number from which they were thrown. The second form of the assertion statement should be used in preference to the first only when the program has some additional information that might help diagnose the failure. For example, if Expression1 involves the relationship between two variables x and y, the second form should be used. Under these circumstances, a reasonable candidate for Expression2 would be "x: " + x + ", y: " + y.In some cases Expression1 may be expensive to evaluate. For example, suppose you write a method to find the minimum element in an unsorted list, and you add an assertion to verify that the selected element is indeed the minimum. The work done by the assert will be at least as expensive as the work done by the method itself. To ensure that assertions are not a performance liability in deployed applications, assertions can be enabled or disabled when the program is started, and are disabled by default. Disabling assertions eliminates their performance penalty entirely. Once disabled, they are essentially equivalent to empty statements in semantics and performance. See Enabling and Disabling Assertions for more information.The addition of the assert keyword to the Java programming language has implications for existing code. SeeCompatibility With Existing Programsfor more informationPutting Assertions Into Your CodeThere are many situations where it is good to use assertions, including:Internal InvariantsControl-Flow InvariantsPreconditions, Postconditions, and Class InvariantsThere are also situations where you should not use them:Do not use assertions for argument checking in public methods.Argument checking is typically part of the published specifications (or contract) of a method, and these specifications must be obeyed whether assertions are enabled or disabled. Another problem with using assertions for argument checking is that erroneous arguments should result in an appropriate runtime exception (such as IllegalArgumentException, IndexOutOfBoundsException, or NullPointerException). An assertion failure will not throw an appropriate exception.Do not use assertions to do any work that your application requires for correct operation.Because assertions may be disabled, programs must not assume that the boolean expression contained in an assertion will be evaluated. Violating this rule has dire consequences. For example, suppose you wanted to remove all of the null elements from a list names, and knew that the list contained one or more nulls. It would be wrong to do this:// Broken! - action is contained in assertionassert names.remove(null);The program would work fine when asserts were enabled, but would fail when they were disabled, as it would no longer remove the null elements from the list. The correct idiom is to perform the action before the assertion and then assert that the action succeeded:// Fixed - action precedes assertionboolean nullsRemoved = names.remove(null);assert nullsRemoved; // Runs whether or not asserts are enabledAs a rule, the expressions contained in assertions should be free of side effects: evaluating the expression should not affect any state that is visible after the evaluation is complete. One exception to this rule is that assertions can modify state that is used only from within other assertions. An idiom that makes use of this exception is presented later in this document.Internal InvariantsBefore assertions were available, many programmers used comments to indicate their assumptions concerning a program's behavior. For example, you might have written something like this to explain your assumption about an else clause in a multiway if-statement:if (i % 3 == 0) {...} else if (i % 3 == 1) {...} else { // We know (i % 3 == 2)...}You should now use an assertion whenever you would have written a comment that asserts an invariant. For example, you should rewrite the previous if-statement like this:if (i % 3 == 0) {...} else if (i % 3 == 1) {...} else {assert i % 3 == 2 : i;...}Note, incidentally, that the assertion in the above example may fail if i is negative, as the % operator is not a true modulus operator, but computes the remainder, which may be negative.Another good candidate for an assertion is a switch statement with no default case. The absence of a default case typically indicates that a programmer believes that one of the cases will always be executed. The assumption that a particular variable will have one of a small number of values is an invariant that should be checked with an assertion. For example, suppose the following switch statement appears in a program that handles playing cards:switch(suit) {case Suit.CLUBS:...break;case Suit.DIAMONDS:...break;case Suit.HEARTS:...break;case Suit.SPADES:...}It probably indicates an assumption that the suit variable will have one of only four values. To test this assumption, you should add the following default case:default:assert false : suit;If the suit variable takes on another value and assertions are enabled, the assert will fail and an AssertionError will be thrown.An acceptable alternative is:default:throw new AssertionError(suit);This alternative offers protection even if assertions are disabled, but the extra protection adds no cost: the throw statement won't execute unless the program has failed. Moreover, the alternative is legal under some circumstances where the assert statement is not. If the enclosing method returns a value, each case in the switch statement contains a return statement, and no return statement follows the switch statement, then it would cause a syntax error to add a default case with an assertion. (The method would return without a value if no case matched and assertions were disabled.)Control-Flow InvariantsThe previous example not only tests an invariant, it also checks an assumption about the application's flow of control. The author of the original switch statement probably assumed not only that the suit variable would always have one of four values, but also that one of the four cases would always be executed. It points out another general area where you should use assertions: place an assertion at any location you assume will not be reached. The assertions statement to use is:assert false;For example, suppose you have a method that looks like this:void foo() {for (...) {if (...)return;}// Execution should never reach this point!!!}Replace the final comment so that the code now reads:void foo() {for (...) {if (...)return;}assert false; // Execution should never reach this point!}Note: Use this technique with discretion. If a statement is unreachable as defined in the Java Language Specification, you will get a compile time error if you try to assert that it is not reached. Again, an acceptable alternative is simply to throw an AssertionError.Preconditions, Postconditions, and Class InvariantsWhile the assert construct is not a full-blown design-by-contract facility, it can help support an informal design-by-contract style of programming. This section shows you how to use asserts for:Preconditions — what must be true when a method is invoked.Lock-Status Preconditions — preconditions concerning whether or not a given lock is held.Postconditions — what must be true after a method completes successfully.Class invariants — what must be true about each instance of a class.PreconditionsBy convention, preconditions on public methods are enforced by explicit checks that throw particular, specified exceptions. For example:/*** Sets the refresh rate.** @param rate refresh rate, in frames per second.* @throws IllegalArgumentException if rate <= 0 or* rate > MAX_REFRESH_RATE.*/public void setRefreshRate(int rate) {// Enforce specified precondition in public methodif (rate <= 0 || rate > MAX_REFRESH_RATE)throw new IllegalArgumentException("Illegal rate: " + rate);setRefreshInterval(1000/rate);}This convention is unaffected by the addition of the assert construct. Do not use assertions to check the parameters of a public method. An assert is inappropriate because the method guarantees that it will always enforce the argument checks. It must check its arguments whether or not assertions are enabled. Further, the assert construct does not throw an exception of the specified type. It can throw only an AssertionError.You can, however, use an assertion to test a nonpublic method's precondition that you believe will be true no matter what a client does with the class. For example, an assertion is appropriate in the following "helper method" that is invoked by the previous method:/*** Sets the refresh interval (which must correspond to a legal frame rate).** @param interval refresh interval in milliseconds.*/private void setRefreshInterval(int interval) {// Confirm adherence to precondition in nonpublic methodassert interval > 0 && interval <= 1000/MAX_REFRESH_RATE : interval;... // Set the refresh interval}Note, the above assertion will fail if MAX_REFRESH_RATE is greater than 1000 and the client selects a refresh rate greater than 1000. This would, in fact, indicate a bug in the library!Lock-Status PreconditionsClasses designed for multithreaded use often have non-public methods with preconditions relating to whether or not some lock is held. For example, it is not uncommon to see something like this:private Object[] a;public synchronized int find(Object key) {return find(key, a, 0, a.length);}// Recursive helper method - always called with a lock on this objectprivate int find(Object key, Object[] arr, int start, int len) {...}A static method called holdsLock has been added to the Thread class to test whether the current thread holds the lock on a specified object. This method can be used in combination with an assert statement to supplement a comment describing a lock-status precondition, as shown in the following example:// Recursive helper method - always called with a lock on this.private int find(Object key, Object[] arr, int start, int len) {assert Thread.holdsLock(this); // lock-status assertion...}Note that it is also possible to write a lock-status assertion asserting that a given lock isn't held.PostconditionsYou can test postcondition with assertions in both public and nonpublic methods. For example, the following public method uses an assert statement to check a post condition:/*** Returns a BigInteger whose value is (this-1 mod m).** @param m the modulus.* @return this-1 mod m.* @throws ArithmeticException m <= 0, or this BigInteger*has no multiplicative inverse mod m (that is, this BigInteger*is not relatively prime to m).*/public BigInteger modInverse(BigInteger m) {if (m.signum <= 0)throw new ArithmeticException("Modulus not positive: " + m);... // Do the computationassert this.multiply(result).mod(m).equals(ONE) : this;return result;}Occasionally it is necessary to save some data prior to performing a computation in order to check a postcondition. You can do this with two assert statements and a simple inner class that saves the state of one or more variables so they can be checked (or rechecked) after the computation. For example, suppose you have a piece of code that looks like this:void foo(int[] array) {// Manipulate array...// At this point, array will contain exactly the ints that it did// prior to manipulation, in the same order.}Here is how you could modify the above method to turn the textual assertion of a postcondition into a functional one:void foo(final int[] array) {// Inner class that saves state and performs final consistency checkclass DataCopy {private int[] arrayCopy;DataCopy() { arrayCopy = (int[]) array.clone(); }boolean isConsistent() { return Arrays.equals(array, arrayCopy); }}DataCopy copy = null;// Always succeeds; has side effect of saving a copy of arrayassert ((copy = new DataCopy()) != null);... // Manipulate array// Ensure array has same ints in same order as before manipulation.assert copy.isConsistent();}You can easily generalize this idiom to save more than one data field, and to test arbitrarily complex assertions concerning pre-computation and post-computation values.You might be tempted to replace the first assert statement (which is executed solely for its side-effect) by the following, more expressive statement:copy = new DataCopy();Don't make this replacement. The statement above would copy the array whether or not asserts were enabled, violating the principle that assertions should have no cost when disabled.Class InvariantsA class invariant is a type of internal invariant that applies to every instance of a class at all times, except when an instance is in transition from one consistent state to another. A class invariant can specify the relationships among multiple attributes, and should be true before and after any method completes. For example, suppose you implement a balanced tree data structure of some sort. A class invariant might be that the tree is balanced and properly ordered.The assertion mechanism does not enforce any particular style for checking invariants. It is sometimes convenient, though, to combine the expressions that check required constraints into a single internal method that can be called by assertions. Continuing the balanced tree example, it might be appropriate to implement a private method that checked that the tree was indeed balanced as per the dictates of the data structure:// Returns true if this tree is properly balancedprivate boolean balanced() {...}Because this method checks a constraint that should be true before and after any method completes, each public method and constructor should contain the following line immediately prior to its return:assert balanced();It is generally unnecessary to place similar checks at the head of each public method unless the data structure is implemented by native methods. In this case, it is possible that a memory corruption bug could corrupt a "native peer" data structure in between method invocations. A failure of the assertion at the head of such a method would indicate that such memory corruption had occurred. Similarly, it may be advisable to include class invariant checks at the heads of methods in classes whose state is modifiable by other classes. (Better yet, design classes so that their state is not directly visible to other classes!)Advanced UsesThe following sections discuss topics that apply only to resource-constrained devices and to systems where asserts must not be disabled in the field. If you have no interest in these topics, skip to the next section, "Compiling Files that Use Assertions".Removing all Trace of Assertions from Class FilesProgrammers developing applications for resource-constrained devices may wish to strip assertions out of class files entirely. While this makes it impossible to enable assertions in the field, it also reduces class file size, possibly leading to improved class loading performance. In the absence of a high quality JIT, it could lead to decreased footprint and improved runtime performance.The assertion facility offers no direct support for stripping assertions out of class files. The assert statement may, however, be used in conjunction with the "conditional compilation" idiom described in the Java Language Specification, enabling the compiler to eliminate all traces of these asserts from the class files that it generates:static final boolean asserts = ... ; // false to eliminate assertsif (asserts)assert <expr> ;Requiring that Assertions are EnabledProgrammers of certain critical systems might wish to ensure that assertions are not disabled in the field. The following static initialization idiom prevents a class from being initialized if its assertions have been disabled:static {boolean assertsEnabled = false;assert assertsEnabled = true; // Intentional side effect!!!if (!assertsEnabled)throw new RuntimeException("Asserts must be enabled!!!");}Put this static-initializer at the top of your class.Compiling Files That Use AssertionsIn order for the javac compiler to accept code containing assertions, you must use the -source 1.4 command-line option as in this example:javac -source 1.4 MyClass.javaThis flag is necessary so as not to cause source compatibility problems.Enabling and Disabling AssertionsBy default, assertions are disabled at runtime. Two command-line switches allow you to selectively enable or disable assertions.To enable assertions at various granularities, use the -enableassertions, or -ea, switch. To disable assertions at various granularities, use the -disableassertions, or -da, switch. You specify the granularity with the arguments that you provide to the switch:no argumentsEnables or disables assertions in all classes except system classes.packageName...Enables or disables assertions in the named package and any subpackages....Enables or disables assertions in the unnamed package in the current working directory.classNameEnables or disables assertions in the named classFor example, the following command runs a program, BatTutor, with assertions enabled in only package com.wombat.fruitbat and its subpackages:java -ea:com.wombat.fruitbat... BatTutorIf a single command line contains multiple instances of these switches, they are processed in order before loading any classes. For example, the following command runs the BatTutor program with assertions enabled in package com.wombat.fruitbat but disabled in class com.wombat.fruitbat.Brickbat:java -ea:com.wombat.fruitbat... -da:com.wombat.fruitbat.Brickbat BatTutorThe above switches apply to all class loaders. With one exception, they also apply to system classes (which do not have an explicit class loader). The exception concerns the switches with no arguments, which (as indicated above) do not apply to system classes.This behavior makes it easy to enable asserts in all classes except for system classes, which is commonly desirable.To enable assertions in all system classes, use a different switch: -enablesystemassertions, or -esa. Similarly, to disable assertions in system classes, use -disablesystemassertions, or -dsa.For example, the following command runs the BatTutor program with assertions enabled in system classes, as well as in the com.wombat.fruitbat package and its subpackages:java -esa -ea:com.wombat.fruitbat...The assertion status of a class (enabled or disabled) is set at the time it is initialized, and does not change. There is, however, one corner case that demands special treatment. It is possible, though generally not desirable, to execute methods or constructors prior to initialization. This can happen when a class hierarchy contains a circularity in its static initialization.If an assert statement executes before its class is initialized, the execution must behave as if assertions were enabled in the class. This topic is discussed in detail in the assertions specification in the Java Language Specification.Compatibility With Existing ProgramsThe addition of the assert keyword to the Java programming language does not cause any problems with preexisting binaries (.class files). If you try to compile an application that uses assert as an identifier, however, you will receive a warning or error message. In order to ease the transition from a world where assert is a legal identifier to one where it isn't, the compiler supports two modes of operation in this release:source mode 1.3 (default) — the compiler accepts programs that use assert as an identifier, but issues warnings. In this mode, programs are not permitted to use the assert statement.source mode 1.4 — the compiler generates an error message if the program uses assert as an identifier. In this mode, programs are permitted to use the assert statement.Unless you specifically request source mode 1.4 with the -source 1.4 flag, the compiler operates in source mode 1.3. If you forget to use this flag, programs that use the new assert statement will not compile. Having the compiler use the old semantics as its default behavior (that is, allowing assert to be used as an identifier) was done for maximal source compatibility. Source mode 1.3 is likely to be phased out over time.Design FAQHere is a collection of frequently asked questions concerning the design of the assertion facility.General QuestionsCompatibilitySyntax and SemanticsThe AssertionError ClassEnabling and Disabling AssertionsGeneral QuestionsWhy provide an assertion facility, given that one can program assertions atop the Java programming language with no special support?Although ad hoc implementations are possible, they are of necessity either ugly (requiring an if statement for each assertion) or inefficient (evaluating the condition even if assertions are disabled). Further, each ad hoc implementation has its own means of enabling and disabling assertions, which lessens the utility of these implementations, especially for debugging in the field. As a result of these shortcomings, assertions have never become a part of the culture among engineers using the Java programming language. Adding assertion support to the platform stands a good chance of rectifying this situation.Why does this facility justify a language change, as opposed to a library solution?We recognize that a language change is a serious effort, not to be undertaken lightly. The library approach was considered. It was, however, deemed essential that the runtime cost of assertions be negligible if they are disabled. In order to achieve this with a library, the programmer is forced to hard-code each assertion as an if statement. Many programmers would not do this. Either they would omit the if statement and performance would suffer, or they would ignore the facility entirely. Note also that assertions were contained in James Gosling's original specification for the Java programming language. Assertions were removed from the Oak specification because time constraints prevented a satisfactory design and implementation.Why not provide a full-fledged design-by-contract facility with preconditions, postconditions and class invariants, like the one in the Eiffel programming language?We considered providing such a facility, but were unable to convince ourselves that it is possible to graft it onto the Java programming language without massive changes to the Java platform libraries, and massive inconsistencies between old and new libraries. Further, we were not convinced that such a facility would preserve the simplicity that is the hallmark of the Java programming language. On balance, we came to the conclusion that a simple boolean assertion facility was a fairly straight-forward solution and far less risky. It's worth noting that adding a boolean assertion facility to the language doesn't preclude adding a full-fledged design-by-contract facility at some time in the future.The simple assertion facility does enable a limited form of design-by-contract style programming. The assert statement is appropriate for nonpublic precondition, postcondition and class invariant checking. Public precondition checking should still be performed by checks inside methods that result in particular, documented exceptions, such as IllegalArgumentException and IllegalStateException.In addition to boolean assertions, why not provide an assert-like construct to suppress the execution of an entire block of code if assertions are disabled?Providing such a construct would encourage programmers to put complex assertions inline, when they are better relegated to separate methods.CompatibilityWon't the new keyword cause compatibility problems with existing programs that use assert as an identifier?Yes, for source files. (Binaries for classes that use assert as an identifier will continue to work fine.) To ease the transition, we implemented a strategy whereby developers can continue using assert as an identifier during a transitional period.Doesn't this facility produce class files that cannot be run against older JREs?Yes. Class files will contain calls to the new ClassLoader and Class methods, such as desiredAssertionStatus. If a class file containing calls to these methods is run against an older JRE (whose ClassLoader class doesn't define the methods), the program will fail at run time, throwing a NoSuchMethodError. It is generally the case that programs using new facilities are not compatible with older releases.Syntax and SemanticsWhy allow primitive types in Expression2?There is no compelling reason to restrict the type of this expression. Allowing arbitrary types provides convenience for developers who, for example, want to associate a unique integer code with each assertion. Further, it makes this expression feel like the argument of System.out.println(...), which is seen as desirable.The AssertionError ClassWhen an AssertionError is generated by an assert statement in which Expression2 is absent, why isn't the program text of the asserted condition used as the detail message (for example, "height < maxHeight")?While doing so might improve out-of-the-box usefulness of assertions in some cases, the benefit doesn't justify the cost of adding all those string constants to .class files and runtime images.Why doesn't an AssertionError allow access to the object that generated it? Similarly, why not pass an arbitrary object from the assertion to the AssertionError constructor in place of a detail message?Access to these objects would encourage programmers to attempt to recover from assertion failures, which defeats the purpose of the facility.Why not provide context accessors (like getFile, getline, getMethod) on AssertionError?This facility is best provided on Throwable, so it may be used for all throwables, not just assertion errors. We enhanced Throwable with the getStackTrace method to provide this functionality.Why is AssertionError a subclass of Error rather than RuntimeException?This issue was controversial. The expert group discussed it at length, and came to the conclusion that Error was more appropriate to discourage programmers from attempting to recover from assertion failures. It is, in general, difficult or impossible to localize the source of an assertion failure. Such a failure indicates that the program is operating "outside of known space," and attempts to continue execution are likely to be harmful. Further, convention dictates that methods specify most runtime exceptions they may throw (with @throws doc comments). It makes little sense to include in a method's specification the circumstances under which it may generate an assertion failure. Such information may be regarded as an implementation detail, which can change from implementation to implementation and release to release.Enabling and Disabling AssertionsWhy not provide a compiler flag to completely eliminate assertions from object files?It is a firm requirement that it be possible to enable assertions in the field, for enhanced serviceability. It would have been possible to also permit developers to eliminate assertions from object files at compile time. Assertions can contain side effects, though they should not, and such a flag could therefore alter the behavior of a program in significant ways. It is viewed as good thing that there is only one semantics associated with each valid Java program. Also, we want to encourage users to leave asserts in object files so they can be enabled in the field. Finally, the spec demands that assertions behave as if enabled when a class runs before it is initialized. It would be impossible to offer these semantics if assertions were stripped from the class file. Note, however, that the standard "conditional compilation idiom" described in the Java Language Specification can be used to achieve this effect for developers who really want it.Why do the commands that enable and disable assertions use package-tree semantics instead of the more traditional package semantics?Hierarchical control is useful, as programmers really do use package hierarchies to organize their code. For example, package-tree semantics allow assertions to be enabled or disabled in all of Swing at one time.Why does setClassAssertionStatus return a boolean instead of throwing an exception if it is invoked when it's too late to set the assertion status (that is, if the named class has already been initialized)?No action (other than perhaps a warning message) is necessary or desirable if it's too late to set the assertion status. An exception seems unduly heavyweight.Why not overload a single method name to take the place of setDefaultAssertionStatus and setAssertionStatus?Clarity in method naming is for the greater good. Overloading tends to cause confusion.Why not tweak the semantics of desiredAssertionStatus to make it more "programmer friendly" by returning the actual assertion status if a class is already initialized?It's not clear that there would be any use for the resulting method. The method isn't designed for application programmer use, and it seems inadvisable to make it slower and more complex than necessary.Why is there no RuntimePermission to prevent applets from enabling/disabling assertions?While applets have no reason to call any of the ClassLoader methods for modifying assertion status, allowing them to do so seems harmless. At worst, an applet can mount a weak denial-of-service attack by enabling assertions in classes that have yet to be initialized. Moreover, applets can only affect the assert status of classes that are to be loaded by class loaders that the applets can access. There already exists a RuntimePermission to prevent untrusted code from gaining access to class loaders (getClassLoader).Why not provide a construct to query the assert status of the containing class?Such a construct would encourage people to inline complex assertion code, which we view as a bad thing. Further, it is straightforward to query the assert status atop the current API, if you feel you must:boolean assertsEnabled = false;assert assertsEnabled = true; // Intentional side-effect!!!// Now assertsEnabled is set to the correct valueWhy does an assert statement that executes before its class is initialized behave as if assertions were enabled in the class?Few programmers are aware of the fact that a class's constructors and methods can run prior to its initialization. When this happens, it is quite likely that the class's invariants have not yet been established, which can cause serious and subtle bugs. Any assertion that executes in this state is likely to fail, alerting the programmer to the problem. Thus, it is generally helpful to the programmer to execute all assertions encountered while in this state.