Variables are used to store data in a program. In the program in Listing 2.1, radius and area are variables of double-precision, floating-point type. You can assign any numerical value to radius and area , and the values of radius and area can be reassigned. For example, you can write the code shown below to compute the area for different radii:
// Compute the first area radius = 1.0 ; area = radius * radius * 3.14159; System.out.println( "The area is " + area + " for radius " + radius); // Compute the second area radius = 2.0 ; area = radius * radius * 3.14159; System.out.println( "The area is " + area + " for radius " + radius);
Variables are for representing data of a certain type. To use a variable, you declare it by telling the compiler the name of the variable as well as what type of data it represents. This is called a variable declaration . Declaring a variable tells the compiler to allocate appropriate memory space for the variable based on its data type. The syntax for declaring a variable is:
datatype variableName;
Here are some examples of variable declarations:
int x; // Declare x to be an integer variable; double radius; // Declare radius to be a double variable; double interestRate; // Declare interestRate to be a double variable; char a; // Declare a to be a character variable;
The examples use the data types int , double , and char . Later you will be introduced to additional data types, such as byte , short , long , float , and boolean .
If variables are of the same type, they can be declared together, as follows :
datatype variable1, variable2, ..., variablen;
The variables are separated by commas. For example,
int i, j, k; // Declare i, j, and k as int variables
Note
By convention, variable names are in lowercase. If a name consists of several words, concatenate all of them and capitalize the first letter of each word except the first. Examples of variables are radius and interestRate . |