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Branching Statements

The Java programming language supports three branching statements:

• The break statement
• The continue statement
• The return statement

The break statement and the continue statement, which are covered next, can be used with or without a label. A label is an identifier placed before a statement. The label is followed by a colon (:):

statementName: someJavaStatement ;

You'll see an example of a label within the context of a program in the next section.

The break statement has two forms: unlabelled and labelled. You saw the break statement in action within the switch statement earlier. As noted there, break terminates enclosing the switch statement and flow of control transfers to the statement immediately following the switch. You can also use the unlabelled form of the break statement to terminate a for, while, or do-while loop. The following sample program, BreakDemo, contains a for loop that searches for a particular value within an array:

public class BreakDemo {
    public static void main(String[] args) {

        int[] arrayOfInts = { 32, 87, 3, 589, 12, 1076,
                              2000, 8, 622, 127 };
        int searchfor = 12;

        int i = 0;
        boolean foundIt = false;

        for ( ; i < arrayOfInts.length; i++) {
            if (arrayOfInts[i] == searchfor) {
                foundIt = true;
                break;
	    }
        }

        if (foundIt) {
	    System.out.println("Found " + searchfor + " at index " + i);
        } else {
	    System.out.println(searchfor + "not in the array");
        }
    }
}

The break statement terminates the for loop when the value is found. The flow of control transfers to the statement following the enclosing for, which is the print statement at the end of the program.

The output of this program is:

Found 12 at index 4

While, the unlabelled form of the break statement is used to terminate the innermost switch, for, while, or do-while, the labelled form terminates an outer statement, which is identified by the label specified in the break statement. The following program, BreakWithLabelDemo, is similar to the previous, but it searches for a value in a two-dimensional array. Two nested for loops traverse the array. When the value is found, a labelled break terminates the statement labelled searchfor loop:

public class BreakWithLabelDemo {
    public static void main(String[] args) {

        int[][] arrayOfInts = { { 32, 87, 3, 589 },
                                { 12, 1076, 2000, 8 },
                                { 622, 127, 77, 955 }
                              };
        int searchfor = 12;

        int i = 0;
        int j = 0;
        boolean foundIt = false;

    search:
        for ( ; i < arrayOfInts.length; i++) {
            for (j = 0; j < arrayOfInts[i].length; j++) {
                if (arrayOfInts[i][j] == searchfor) {
                    foundIt = true;
                    break search;
	        }
            }
        }

        if (foundIt) {
	    System.out.println("Found " + searchfor + " at " + i + ", " + j);
        } else {
            System.out.println(searchfor + "not in the array");
        }

    }
}

The output of this program is:

Found 12 at 1, 0

This syntax can be a little confusing. The break statement terminates the labelled statement; it does not transfer the flow of control to the label. The flow of control transfers to the statement immediately following the labelled (terminated) statement.

You use the continue statement to skip the current iteration of a for, while , or do-while loop. The unlabelled form skips to the end of the innermost loop's body and evaluates the boolean expression that controls the loop, basically skipping the remainder of this iteration of the loop. The following program, ContinueDemo, steps through a string buffer checking each letter. If the current character is not a `p', the continue statement skips the rest of the loop and proceeds to the next character. If it is a `p'. the program increments a counter, and converts the `p' to an uppercase letter

public class ContinueDemo {
    public static void main(String[] args) {

        StringBuffer searchMe = new StringBuffer(
                  "peter piper picked a peck of pickled peppers");
        int max = searchMe.length();
        int numPs = 0;

        for (int i = 0; i < max; i++) {
	    //interested only in p's
            if (searchMe.charAt(i) != 'p')
	        continue;

	    //process p's
	    numPs++;
            searchMe.setCharAt(i, 'P');
        }
        System.out.println("Found " + numPs + " p's in the string.");
        System.out.println(searchMe);
    }
}

Here is the output of this program:

Found 9 p's in the string.
Peter PiPer Picked a Peck of Pickled PePPers

The labelled form of the continue statement skips the current iteration of an outer loop marked with the given label. The following example program, ContinueWithLabelDemo, uses nested loops to search for a substring within another string. Two nested loops are required: one to iterate over the substring, and one to iterate over the string being searched. This program uses the labelled form of continue to skip an iteration in the outer loop:

public class ContinueWithLabelDemo {
    public static void main(String[] args) {

        String searchMe = "Look for a substring in me";
        String substring = "sub";
        boolean foundIt = false;

        int max = searchMe.length() - substring.length();  

    test:
        for (int i = 0; i <= max; i++) {
            int n = substring.length();
            int j = i;
            int k = 0;
            while (n-- != 0) {
                if (searchMe.charAt(j++) != substring.charAt(k++)) {
                    continue test;
                }
            }    
            foundIt = true;
            break test;
        }
        System.out.println(foundIt ? "Found it" : "Didn't find it");
    }
}

Here is the output from this program:

Found it

The last of Java's branching statements is the return statement. You use return to exit from the current method and jump back to the statement within the calling method that follows the original method call. There are two forms of return: one that returns a value and one that doesn't. To return a value, simply put the value (or an expression that calculates the value after the return keyword:

return ++count;

The value returned by return must match the type of method's declared return value.

When a method is declared void use the form of return that doesn't return a value:

return;

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