Variable stores value in a Java program
In this chapter you will learn:
Declaring a Variable
A variable is defined by an identifier, a type, and an optional initializer. The variables also have a scope(visibility / lifetime).
In Java, all variables must be declared before they can be used. The basic form of a variable declaration is shown here:
type identifier [ = value][, identifier [= value] ...] ;
There are three parts in variable definition:
typecould beintorfloat.identifieris the variable's name.- Initialization includes an equal sign and a value.
To declare more than one variable of the specified type, use a comma-separated list.
int a, b, c; // declares three ints, a, b, and c.
int d = 3, e, f = 5; // declares three more ints, initializing d and f.
The following variables are defined and initialized in one expression.
public class Main {
public static void main(String[] argv) {
byte z = 2; // initializes z.
double pi = 3.14; // declares an approximation of pi.
char x = 'x'; // the variable x has the value 'x'.
}/*from j av a 2s . co m*/
}
Variable cannot be used prior to its declaration.
public class Main {
public static void main(String[] argv) {
// j av a2 s. c o m
count = 100; // Cannot use count before it is declared!
int count;
}
}
Compiling the code above generates the following error message:
Assignment Operator
The assignment operator is the single equal sign, =. It has this general form:
var = expression;
type of var must be compatible with the type of expression.
The assignment operator allows you to create a chain of assignments.
public class Main {
public static void main(String[] argv) {
int x, y, z;/*from ja v a 2 s. c om*/
x = y = z = 100; // set x, y, and z to 100
System.out.println("x is " + x);
System.out.println("y is " + y);
System.out.println("z is " + z);
}
}
The output:
Dynamic Initialization
Java allows variables to be initialized dynamically.
In the following code the Math.sqrt returns the square root of 2 * 2 and assigns
the result to c directly.
public class Main {
public static void main(String args[]) {
/* ja va2 s . c o m*/
// c is dynamically initialized
double c = Math.sqrt(2 * 2);
System.out.println("c is " + c);
}
}
The output from the code above is
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