7 Nested Classes and Interfaces

7.1

// 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.