Think Java, 2nd Edition

Chapter 2. Variables and Operators

This chapter describes how to write statements using variables, which store values like numbers and words, and operators, which are symbols that perform a computation. We also explain three kinds of programming errors and offer additional debugging advice.

To run the examples in this chapter, you will need to create a new Java class with a main method (see “The Hello World Program”). Throughout the book, we often omit class and method definitions to keep the examples concise.

Declaring Variables

One of the most powerful features of a programming language is the ability to define and manipulate variables. A variable is a named location in memory that stores a value. Values may be numbers, text, images, sounds, and other types of data. To store a value, you first have to declare a variable:

String message;

This statement is called a declaration, because it declares that the variable message has the type String. Each variable has a type that determines what kind of values it can store. For example, the int type can store integers like 1 and -5, and the char type can store characters like 'A' and 'z'.

Some types begin with a capital letter and some with lowercase. You will learn the significance of this distinction later, but for now you should take care to get it right. There is no such type as Int or string.

To declare an integer variable named x, you simply type this:

int x;

Note that x is an arbitrary name for the variable. In general, you should ...