[Chapter 6] 6.6 The switch Statement
Author: Mark Grand
Date: Thu Jul 31 13:14:29 1997

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| Chapter 6 Statements and Control Structures |

## 6.6 The switch Statement

A `switch` statement selects a specially labeled statement in its block as the next statement to be executed, based on the value of an expression:

In Java, the type of the expression in parentheses must be `byte`, `char`, `short`, or `int`. This is unlike C/C++, which allows the type of a `switch` statement to be any integer type, including `long`.

The body of a `switch` statement must be a block. The top-level statements inside a `switch` may contain `case` labels. The expression following a `case` label must be a constant expression that is assignable to the type of the `switch` expression. No two `case` labels in a `switch` can contain the same value. At most one of the top-level statements in a `switch` can contain a `default` label.

A `switch` statement does the following:

- Evaluates the expression in parentheses. If the type of the expression is not `int`, the value produced by the expression is converted to `int`.

- Compares the value produced by the expression to the values in the `case` labels. Prior to comparison, the value in the `case` label is converted to `int` if it is not already `int`.

- If a `case` label is found that has the same value as the expression, that label's statement is the next statement to be executed.

- If no `case` label is found with the same value as the expression, and a statement in the block has a `default` label, that statement is the next one to be executed.

- If there is no statement in the block that has a `default` label, the statement after the `switch` statement is the next statement to be executed.

Here's an example of a `switch` statement:

    switch (rc) {
      case 1:
        msg = "Syntax error";
        break;
      case 2:
        msg = "Undefined variable";
        break;
      default:
        msg = "Unknown error";
        break;
    }

After the `switch` statement has transferred control to a `case`-labeled statement, statements are executed sequentially in the normal manner. Any `case` labels and the `default` label have no further effect on the flow of control. If no statement inside the block alters the flow of control, each statement is executed in sequence with control flowing past each `case` label and out the bottom of the block. The following example illustrates this behavior:

    void doInNTimes(int n){
        switch (n > 5 ? 5 : n) {
          case 5:
            doIt();
          case 4:
            doIt();
          case 3:
            doIt();
          case 2:
            doIt();
          case 1:
            doIt();
        }
    }

The above method calls the `doIt()` method up to 5 times.

To prevent control from flowing through `case` labels, it is common to end each `case` with a flow-altering statement such as a `break` statement. Other statements used for this purpose include the `continue` statement and the `return` statement.

References Constant Expressions; Expression 4; Identifiers; Integer types; Local Classes; Local Variables; Statement 6; The break Statement; The continue Statement; The return Statement

The if Statement |  | Iteration Statements