Primitive Data Types Expressions And Variables: Fill & Download for Free

Unlike the C++ standard, Java Language Specification simply refuses to treat void as a type, leaving a hole in the type system. It appears intentional, and internally inconsistent:The authoritative list of types in the Java programming language can be found in JLS chapter 4. Types, Values, and Variables, which says (emphasis mine)The types of the Java programming language are divided into two categories: primitive types and reference types. The primitive types are the boolean type and the numeric types. The numeric types are the integral types byte, short, int, long, and char, and the floating-point types float and double. The reference types are class types, interface types, and array types. There is also a special null type, the type of the expression null, which has no name.However, in chapter 8.4.5 Method Result it calls void a type:A method declaration d1 with return type R1 is return-type-substitutable for another method d2 with return type R2 iff any of the following is true:If R1 is void then R2 is void.Chapter 4 also says, in its very first sentence,every expression has a typeHowever, chapter 15.3 Type of an Expression contradicts that, sayingIf an expression denotes a variable or a value, then the expression has a typeAnd earlier up in 15.1 Evaluation, Denotation, and Result it defines that exception as “methods declared void”:An expression denotes nothing if and only if it is a method invocation that invokes a method that does not return a value, that is, a method declared void.In short, it appears to be an arbitrary decision on behalf of the Java language specification authors. The approach used in C++ is more consistent (every expression has a type, no matter what), and so is the approach taken by other JVM languages: the methods that return void in Java return Unit in Scala, which is a perfectly ordinary class type, much like Java’s own java.lang.Void

In my opinion, if you are completely a beginner,start by learning the fundamentals of Java programming. You should familiarize yourself with the following:primitive data types,variables,constants,assignments,expressions,operatorsselection statementsmathematical functions,charactersstringsloopsmethodsarraysrecursive methodsObject-Oriented ProgrammingData Structures and AlgorithmsWith all those tools in your programming toolset, you have the power to create powerful and efficient softwares(Android), usable by the society for a better life.All the best!

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