7 Nested Classes and Interfaces

// Filename: Exercise3.java
interface Function {
    public int evaluate(int arg);
}

class Half implements Function {
    public int evaluate(int arg) {
        return arg/2;
    }
}

class Print implements Function {
    public int evaluate(int arg) {
        System.out.println(arg);
        return arg;
    }
}

public class Exercise3 {
    /* Inner class that applies the function, prints the value, and
       returns the result. */
    static class PrintFunc extends Print {
        PrintFunc(Function f) {
            func = f;
        }

        Function func;

        public int evaluate(int arg) {
            return super.evaluate(func.evaluate(arg));
        }
    }

    // Inner class that just returns the argument unchanged.
    /* Use this when you want a PrintFunc object to print
       the argument as-is. */
    static class NoOpFunc implements Function {
        public int evaluate(int arg) {
            return arg;
        }
    }

    public static void main(String[] args) {
        // Create array with values 1 .. 10
        int[] myArr = new int[10];
        for (int i=0; i<10;) myArr[i] = ++i;

        // Print array without modification
        applyFunctionToArray(myArr, new PrintFunc(new NoOpFunc()));

        // Print halved values
        applyFunctionToArray(myArr, new PrintFunc(new Half()));
    }

    public static int[] applyFunctionToArray(int[] arrIn, Function func) {
        int length = arrIn.length;
        int[] arrOut = new int[length];

        for (int i=0; i< length; i++)
            arrOut[i] = func.evaluate(arrIn[i]);

        return arrOut;
    }
}

The output when run is the same as in Exercise 6.2.