JavaBasic syntax and simple programsControl flow statements

Switch statement

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Three keywords: switch, case and default

Suppose you need to write a program that performs different actions depending on the value of a variable. For example, maybe you need to choose an action in a menu of a game. To do that you can use a conditional statement with multiple branches as shown below. 

int action = ...; // a certain value from 1 to 3
        
if (action == 1) {
    System.out.println("Starting a new game...");
} else if (action == 2) {
    System.out.println("Loading a saved game");
} else if (action == 3) {
    System.out.println("Displaying help...");
} else if (action == 4) {
    System.out.println("Exiting...");
} else {
    System.out.println("Unsuitable action, please, try again");
}

Of course, this code handles the task. But if your conditional statement has a lot of branches, it can be hard to understand.

The switch statement provides a way to choose between multiple cases based on the value of a single variable (not an expression!). The variable can be an integer number, character, string, or enumeration. The last two types will be studied further.

Using the switch statement, the previous code will look like this:

switch (action) {
    case 1:
        System.out.println("Starting a new game...");
        break;
    case 2:
        System.out.println("Loading a saved game");
        break;
    case 3:
        System.out.println("Displaying help...");
        break;
    case 4:
        System.out.println("Exiting...");
        break;
    default:
        System.out.println("Unsuitable action, please, try again");
}

As you may note, this code is well-structured and easier to read than the equal conditional statement.

The general form of the switch statement

The most general form of the switch statement is the following
switch (variable) {
    case value1:
        // do something here
        break;
    case value2:
        // do something here
        break;
    
    //... other cases
    
    case valueN:
        // do something here
        break;
    default:
        // do something by default
}

The switch and case keywords are always required here. The keywords break and default are optional. The keyword break stops the execution of the whole switch statement, not just one case.

If a case does not have the break-keyword, the following case will be also evaluated. The default case is evaluated if no any case matches the variable value.

An example with "zero", "one" and "two"

Let's consider another example. The following code outputs the names of integer numbers or a default text. It has three base cases and one default case.

int val = ...;
switch (val) {
     case 0:
         System.out.println("zero");
         break;
     case 1:
         System.out.println("one");
         break;
     case 2:
         System.out.println("two");
         break;
     default:
         System.out.println("The value is less than zero or greater than two");
}

If the val is 0, the code prints:

zero

If the val is 1, the code prints:

one

if the val is 10, the code prints:

The value is less than zero or greater than two

If you forget the keyword break in a case, the compiler won't consider it an error. Let's remove it from the second case (case 1) and assign 1 to val. The program prints:

one
two

Omitting break keyword is not a good practice. Try to avoid it.

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