// CS 3723.  Example showing how to pass a function as
//   a parameter in Java. The function is embedded in an
//   interface, and then different implementations of the
//   interface are used.


// Sorter.java: interface holds a generic sort routine
public interface Sorter {
   public void sort(int[] a);
}

// BubbleSort.java: implements sort using a bubblesort
public class BubbleSort implements Sorter {
   // sort: really simple bubblesort algorithm
   public void sort(int[] a) {
      System.out.println("Bubble Sort:");
      int size = a.length;
      for (int dum = 0; dum < size-1; dum++)
         for (int j = 0; j < size-1; j++)
            if (a[j] > a[j+1]) {
               int temp = a[j];
               a[j] = a[j+1];
               a[j+1] = temp;
            }
   }
}

// SelectSort.java: implements sort using a selectsort
public class SelectSort implements Sorter {
   // sort: fairly reasonable selectsort, except for the recursion
   public void sort(int[] a) {
      System.out.println("Select Sort:");
      int n = a.length - 1;
      int maxi;
      while (n > 0) {
         maxi = maxInd(n, a);
         int temp = a[maxi];
         a[maxi] = a[n];
         a[n] = temp;
         n--;
      }
   }

   // maxInt: recursive function just for demonstration purposes
   private int maxInd(int m, int[] a) {
      int maxi;
      if (m == 0) return m;
      maxi = maxInd(m-1, a);
      if (a[m] > a[maxi]) return m;
      return maxi;
   }
}

// MultiSort.java: Demonstration of passing a function as a parameter
public class MultiSort {
   int a[];     // array of ints to be sorted
   Sorter s[];  // array of references to objects holding sort functions
   
   // MultiSort: constructor to allocate stuff
   public MultiSort() {
      a = new int[10];  // actual array of 10 ints
      s = new Sorter[2]; // actual array of 2 refs to objects
      s[0] = new BubbleSort(); // object holding a bubblesort function
      s[1] = new SelectSort(); // object holding a selectsort function
   }
   
   // DoSorts: invoke the two sort routines in order
   public void DoSorts() {
      for (int i = 0; i < s.length; i++)
         execSort(a, s[i]);
   }
   
   // execSort: actually sort, using any sort function
   private void execSort(int[] a, Sorter someSort) {
      initArr(a);
      someSort.sort(a);
      printArr(a);
   }

   // initArr: initialize parameter to hold random ints
   private void initArr(int[] a) {
      for (int i = 0; i < a.length; i++)
         a[i] = (int)(1000.0*Math.random());
   }

   // printArr: print parameter on one line
   private void printArr(int[] a) {
      for (int i = 0; i < a.length; i++)
         System.out.print(a[i] + " ");
      System.out.println();
   }
      
   // main: just create the class and start the sorting
   public static void main(String[] args) {
      MultiSort ms = new MultiSort();
      ms.DoSorts();
   }
}

ten60% javac Sorter.java
ten60% javac BubbleSort.java
ten60% javac SelectSort.java
ten60% javac MultiSort.java
ten60% java MultiSort

Bubble Sort:
29 35 48 355 376 656 692 702 732 868 
Select Sort:
40 251 310 345 505 515 925 967 972 987