Switch statement

You already know how to shape the control flow of a program using if-else statements. Perhaps, you have faced situations when you had to stack and nest multiple if-else statements to get the desired result. In this topic, you will learn an alternative way to deal with multiple choices.

When a conditional statement is not so good

Suppose you need to write a program that performs different actions depending on the value of a variable. For example, choosing an action from the 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 4
        
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 for people.

Three keywords: switch, case, and default

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 can see, this code is well-structured and easier to read than the equal conditional statement. We have not explained the keywords switch, case and break yet, but you can already guess what they mean.

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
        break; // it can be omitted
}

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 evaluated as well, including the default case. The default case is also evaluated if there’s no other case that matches the variable value. The break keyword in the default branch is optional and can be omitted.

A case section may contain any block of code, even a nested switch statement, however it is recommended to avoid deeply nested code structures wherever possible.

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. This switch statement has three base cases and a single 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.

Java 12–14 introduced some new features allowing to use switch as an expression.

Conclusion

When you have a limited number of cases to choose from, switch statements can help you avoid unnecessary nested if-else constructions. For that, you need the switch keyword to introduce the value to evaluate, and case for each of the possible values. Do not forget to also use the break keyword to avoid evaluating extra cases and default branch to indicate the default behavior.