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The for Statement

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PENDING: This page will also discuss the for-each language feature introduced in 5.0. An example is here: ForEachDemo. Compare it to its functional equivalent, ForDemo. Until this page is updated, see the 5.0 guide document The For-Each Loop.

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The for statement provides a compact way to iterate over a range of values. The general form of the for statement can be expressed like this:

for (initialization; termination; increment) {
    statement(s)
}

The initialization is an expression that initializes the loop—it's executed once at the beginning of the loop. The termination expression determines when to terminate the loop. When the expression evaluates to false, the loop terminates. Finally, increment is an expression that gets invoked after each iteration through the loop. All these components are optional. In fact, to write an infinite loop, you omit all three expressions:

for ( ; ; ) {    // infinite loop
    ...
}

Often for loops are used to iterate over the elements in an array or the characters in a string. The following sample, ForDemo, uses a for statement (shown in boldface) to iterate over the elements of an array and to print them:

public class ForDemo {
    public static void main(String[] args) {
        int[] arrayOfInts = { 32, 87, 3, 589, 12, 
                              1076, 2000, 8, 622, 127 };

        for (int i = 0; i < arrayOfInts.length; i++) {
            System.out.print(arrayOfInts[i] + " ");
        }
        System.out.println();
    }
}

The output of the program is: 32 87 3 589 12 1076 2000 8 622 127.

Notice that you can declare a local variable within the initialization expression of a for loop. The scope of this variable extends from its declaration to the end of the block governed by the for statement so it can be used in the termination and increment expressions as well. If the variable that controls a for loop is not needed outside of the loop, it’s best to declare the variable in the initialization expression. The names i, j, and k are often used to control for loops; declaring them within the for loop initialization expression limits their life span and reduces errors.

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