Question

I am just studying a few classes given to me by my lecturer and I can’t understand how the function heapRebuild is being made used of! It doesn’t change any global variables and it doesn’t print out anything ad it doesn’t return anything – so should this even work? It shouldn’t, should it?

If you were told to make use of heapRebuild to make a new function removeMac would you edit heapRebuild?

public class MaxHeap<T extends Comparable<T>> implements Heap<T>{
private T[] heap;
private int lastIndex;

public T removeMax(){
        T rootItem = heap[0];
        heap[0] = heap[lastIndex-1];
        lastIndex--;
        heapRebuild(heap, 0, lastIndex);
        return rootItem;
}

protected void heapRebuild(T[ ] items, int root, int size){

        int child = 2*root+1;
        if( child < size){
            int rightChild = child+1;
            if ((rightChild < size) &&
                    (items[rightChild].compareTo(items[child]) > 0)){
                child = rightChild;
            }
            if (items[root].compareTo(items[child]) < 0){
                T temp = items[root];
                items[root] = items[child];
                items[child] = temp;
                heapRebuild(items, child, size);}
        }
    }

}

Answer 1

Java is a pass-reference-by-value OO language. The methods can change the passed-in mutable values.

Simplified example:

import java.util.Arrays;

public class Test {

    public static void main(String... args) {
        String[] strings = new String[] { "foo", "bar" };
        System.out.println(Arrays.toString(strings)); // [foo, bar]
        changeValue(strings);
        System.out.println(Arrays.toString(strings)); // [foo, foo]
    }

    public static void changeValue(String[] strings) {
        strings[1] = "foo";
    }

}