Think Java

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.

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 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 a declaration, because it declares that the variable named 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, and the char type can store characters.

Some types begin with a capital letter and some with lowercase. We 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:

int x;

Note that x is an arbitrary name for the variable. In general, you should use names that indicate what the variables mean. For example, if you saw these declarations, you could probably guess what values would be stored:

String firstName;
String lastName;
int hour, minute;

This example declares two variables with type String and two with type