[Chapter 6] 6.8 The break Statement
Author: Mark Grand
Date: Thu Jul 31 13:14:36 1997

#

| Chapter 6 Statements and Control Structures |

## 6.8 The break Statement

A `break` statement transfers control out of an enclosing statement:

If a `break` statement does not contain an identifier, the statement attempts to transfer control to the statement that follows the innermost enclosing `while`, `for`, `do`, or `switch` statement. The Java compiler issues an error message if a `break` statement without an identifier occurs without an enclosing `while`, `for`, `do`, or `switch` statement. Here is an example of a `break` statement that contains no identifier:

    while (true) {
        c = in.read();
        if (Character.isSpace(c)
            break;
        s += (char)c;
    }

In this example, the `break` statement is used to exit from the `while` loop.

The innermost `while`, `for`, `do`, or `switch` statement that encloses the `break` statement must be in the immediately enclosing method or initializer block. In other words, a `break` statement cannot be used to leave a method or initializer block. The `break` statement in the following example is used incorrectly and generates an error:

    while (true) {
        class X {
            void doIt() {
                break;
            }
        }
        new X().doIt();
    }

If a `break` statement contains an identifier, the identifier must be defined as the label of an enclosing statement. A `break` statement that contains an identifier attempts to transfer control to the statement that immediately follows the statement labeled with that identifier. Here's an example of a `break` statement that contains an identifier:

    foo:{
        doIt();
        if (n > 4) break foo;
        doIt();
    }

In this example, the `break` statement transfers control to the statement following the block labeled `foo`.

The label used in a `break` statement must be in the immediately enclosing method or initializer block. The `break` statement in the following example is used incorrectly and generates an error:

    foo: {
        class X {
            void doIt() {
                break foo;
            }
        }
        new X().doIt();
    }

The statement to which a `break` statement attempts to transfer control is called the target statement. If a `break` statement occurs inside a `try` statement, control may not immediately transfer to the target statement. If a `try` statement has a `finally` clause, the `finally` block is executed before control leaves the `try` statement for any reason. This means that if a `break` statement occurs inside a `try` statement (but not in its `finally` block) and the target statement is outside of the `try` statement, the `finally` block is executed first, before the control transfer can take place.

If the `finally` block contains a `break`, `continue`, `return`, or `throw` statement, the pending control transfer for the previously executed `break` statement is forgotten. Instead, control is transferred to the target of the `break`, `continue`, `return`, or `throw` statement in the `finally` block.

If the `finally` block does not contain a `break`, `continue`, `return`, or `throw` statement, the pending control transfer happens after the `finally` block is done executing, unless the target statement is enclosed by another `try` statement. If there is another enclosing `try` statement and it has a `finally` clause, that `finally` block is also executed before the control transfer can take place. Execution proceeds in this manner until the target statement of the `break` is executed.

Here is an example that illustrates a simple scenario:

    ll:{
        try {
            f = new FileInputStream(fname);
            i = f.read();
            if (i != ' ')
                break ll;
            i = f.read();
        } catch (IOException e) {
            System.out.println("Got an IO Exception!");
            break ll;
        } finally {
            f.close();           // Always executed
        }
        // Only reached if we don't break out of the try
        System.out.println("No breaks");
    }

In this example, a `break` statement is executed if one of two things happens. First, if an `IOException` is thrown, the `catch` clause prints a message and then executes a `break` statement. Otherwise, if the first call to `read()` does not return a space, a `break` statement is executed. In either case, the `finally` clause is executed before control is transferred to the statement following the statement labeled with `ll`.

References Identifiers; Labeled Statements; The continue Statement; The do Statement; The for Statement; The return Statement; The throw Statement; The try Statement; The while Statement

Iteration Statements |  | The continue Statement