Chapter 2

Programs, Data, Variables, and Calculation


  • How to declare and define variables of the basic integer and floating-point types
  • How to write an assignment statement
  • How integer and floating-point expressions are evaluated
  • How to output data from a console program
  • How mixed integer and floating-point expressions are evaluated
  • What casting is and when you must use it
  • What boolean variables are
  • What determines the sequence in which operators in an expression are executed
  • How to include comments in your programs

In this chapter you look at the entities in Java that are not objects — numbers and characters. This gives you all the elements of the language you need to perform numerical calculations, and you apply these in a few working examples.


A variable is a named piece of memory that you use to store information in your Java program — an item of data of some description. Each named piece of memory that you define can only store data of one particular type. If you define a variable to store integers, for example, you can’t use it to store a value that is a decimal fraction, such as 0.75. If you’ve defined a variable that you use to refer to a Hat object, you can only use it to reference an object of type Hat (or any of its subclasses, as you will see in Chapter 6). Because the type of data that each variable can store is fixed, the compiler can verify that each variable you define in your program is not used in a manner ...

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