Programming Tutorials

switch in java

By: Jagan in Java Tutorials on 2007-09-07  

The switch statement is Java's multiway branch statement. It provides an easy way to dispatch execution to different parts of your code based on the value of an expression. As such, it often provides a better alternative than a large series of if-else-if statements. Here is the general form of a switch statement:

switch (expression) {
    case value1:
    // statement sequence
    break;
    case value2:
    // statement sequence
    break;
    .
    .
    .
    case valueN:
    // statement sequence
    break;
    default:
    // default statement sequence
    }

The expression must be of type byte, short, int, or char; each of the values specified in the case statements must be of a type compatible with the expression. Each case value must be a unique literal (that is, it must be a constant, not a variable). Duplicate case values are not allowed.

The switch statement works like this: The value of the expression is compared with each of the literal values in the case statements. If a match is found, the code sequence following that case statement is executed. If none of the constants matches the value of the expression, then the default statement is executed. However, the default statement is optional. If no case matches and no default is present, then no further action is taken.

The break statement is used inside the switch to terminate a statement sequence. When a break statement is encountered, execution branches to the first line of code that follows the entire switch statement. This has the effect of "jumping out" of the switch. Here is a simple example that uses a switch statement:

// A simple example of the switch.
class SampleSwitch {
    public static void main(String args[]) {
        for (int i = 0; i < 6; i++)
            switch (i) {
                case 0:
                    System.out.println("i is zero.");
                    break;
                case 1:
                    System.out.println("i is one.");
                    break;
                case 2:
                    System.out.println("i is two.");
                    break;
                case 3:
                    System.out.println("i is three.");
                    break;
                default:
                    System.out.println("i is greater than 3.");
            }
    }
}

The output produced by this program is shown here:

i is zero.
i is one.
i is two.
i is three.
i is greater than 3.
i is greater than 3.

As you can see, each time through the loop, the statements associated with the case constant that matches i are executed. All others are bypassed. After i is greater than 3, no case statements match, so the default statement is executed. The break statement is optional. If you omit the break, execution will continue on into the next case. It is sometimes desirable to have multiple cases without break statements between them. For example, consider the following program:

// In a switch, break statements are optional.
class MissingBreak {
    public static void main(String args[]) {
        for (int i = 0; i < 12; i++)
            switch (i) {
                case 0:
                case 1:
                case 2:
                case 3:
                case 4:
                    System.out.println("i is less than 5");
                    break;
                case 5:
                case 6:
                case 7:
                case 8:
                case 9:
                    System.out.println("i is less than 10");
                    break;
                default:
                    System.out.println("i is 10 or more");
            }
    }
}

This program generates the following output:

i is less than 5
i is less than 5
i is less than 5
i is less than 5
i is less than 5
i is less than 10
i is less than 10
i is less than 10
i is less than 10
i is less than 10
i is 10 or more
i is 10 or more

As you can see, execution falls through each case until a break statement (or the end of the switch) is reached. While the preceding example is, of course, contrived for the sake of illustration, omitting
the break statement has many practical applications in real programs. To sample its more realistic usage, consider the following rewrite of the season example shown earlier. This version uses a switch to provide a more efficient implementation.

// An improved version of the season program.
class Switch {
    public static void main(String args[]) {
        int month = 4;
        String season;
        switch (month) {
            case 12:
            case 1:
            case 2:
                season = "Winter";
                break;
            case 3:
            case 4:
            case 5:
                season = "Spring";
                break;
            case 6:
            case 7:
            case 8:
                season = "Summer";
                break;
            case 9:
            case 10:
            case 11:
                season = "Autumn";
                break;
            default:
                season = "Bogus Month";
        }
        System.out.println("April is in the " + season + ".");
    }
}