Why Do Switch Statements Need Break Statements?

Switch Statements without Break

An error is encountered when a switch statement lacks break statements between cases. Consider the following code snippet:

switch (x) {

    case 0:
        // code

    case 1:
        // code

    case 2:
        // code
}

Explanation

Java's switch statement requires break statements to separate cases. Without break, code in subsequent cases is executed even when the condition matches a previous case. In the example above, if x is 1, both cases 1 and 2 will be executed.

This behavior is typically unintended and can lead to incorrect program logic. Findbugs identifies this potential error and flags it as a warning.

Usage

Break statements are used to terminate the execution of a case and prevent code from falling through to subsequent cases. The following code is grammatically correct and will only execute the code for the matching case:

switch (foo) {
    case 0:
        doSomething();
        break;
    case 1:
        doSomethingElse();
        break;
    default:
        doSomeOtherThing();
        break;
}

Exception

In certain scenarios, it may be desirable to intentionally allow code to fall through to subsequent cases. For example,

switch (foo) {
    case 0:
    case 1:
        doSomething();
        break;
    case 2:
        doSomethingElse();
        break;
    default:
        doSomeOtherThing();
        break;
}

In this case, doSomething() will be executed if foo is either 0 or 1. This is a common pattern known as "fall-through" and is generally considered acceptable when no code appears between the cases (e.g., case 1 and case 2). Most analysis tools will not flag fall-through cases as errors in these situations.

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