So i am trying to make an array based generic heap that i can use with my tester class. Much of what i have is based of my understandings of trees and some research online as well as from my textbook; both which have very limited info on what i am looking for. However, i did manage to get all the methods in need and when i run it, i get this error:
Exception in thread "main" java.lang.ClassCastException: [Ljava.lang.Object; cannot be cast to [Ljava.lang.Comparable;
at q1.Heaps.<init>(Heaps.java:23)
at q1.createGui.<init>(Gui.java:46)
at q1.Gui.main(Gui.java:18)
Im guessing it has to do with how i declare and initialize my Comparable array, which i am having trouble figuring out how to.
package q1;
import java.util.Arrays;
public class Heaps<E extends Comparable<E>> {
Comparable[] data;
int size;
/**
* Constructor with s as size
*/
@SuppressWarnings("unchecked")
public Heaps(int s) {
size = 0;
data = (E[]) new Object[s];
}
/**
* Adds a value to the heap
*/
public void add(E value) {
if (full()) // expand array
ensureCapacity(2*size);
size++;
data[size] = value;
if (size > 1)
heapifyUp();
}
/**
* Checks if the array is full
*/
private boolean full()
{
return (size == data.length-1);
}
private void heapifyUp()
{
Comparable<E> temp;
int next = size;
while (next != 1 && data[next].compareTo(data[next/2]) > 0)
{
temp = data[next];
data[next] = data[next/2];
data[next/2] = temp;
next = next/2;
}
}
private void heapifyDown()
{
Comparable<E> temp;
int next = 0;
while (next*2 <= size) // node has a child
{
int child = 2*next; // left child
if (child < size &&
data[child].compareTo(data[child+1]) > 0)//left smaller than right
child++; // right child instead
if (data[next].compareTo(data[child]) > 0)
{
temp = data[next];
data[next] = data[child];
data[child] = temp;
next = child;
}
else;
next = size; // stop loop
}//end while
}
/**
* Removes all occurrence of element
*/
public boolean removeAll(E element) {
if (contains(element) && !(isEmpty())){
for (int i = 0; i < size; i++){
if(element.equals(data[i])){
data[i] = data[size-1];
}
heapifyDown();
}
return true;
}
return false;
}
/**
* Removes 1st occurrence of element
*/
public boolean remove(E element) {
if (contains(element) && !(isEmpty())){
for (int i = 0; i < size; i++){
if(element.equals(data[i])){
data[i] = data[size-1];
heapifyDown();
return true;
}
}
}
return false;
}
public boolean isEmpty() {
return size == 0;
}
public Comparable<E>[] ensureCapacity(int s) {
return Arrays.copyOf(data, 2*s);
}
/**
* Converts the heap into its String representation.
* @return the String representation
*/
public Comparable<E>[] iteratorPreOrder()
{
Comparable<E>[] temp = (E[]) new Object[size];
temp[0] = data[0];
int i = 1;
int count = 1;
while(data[2*i] != null){
temp[count] = data[2*i];
++i;
++count;
}
i = 1;
while(data[(2*i) +1] != null){
temp[count] = data[(2*i) +1];
++i;
++count;
}
return temp;
}
public int countOccurance(E element){
int count = 0;
for (int i =0; i < size; i++){
if(element.equals(data[i])){
count++;
}
}
return count;
}
public boolean contains (E element)
{
for (int i=0; i<size; i++){
if (element.equals(data[i])){
return true;
}
}
return false;
}
}
If you could please show me how i would solve this problem, i would greatly appreciate it. Thanks
EDIT: SO i edited the my class and now it works when i do data = (E[]) new Comparable[s]. So why does java not allow generic Array types, what makes it different from Arraylist, Stacks, Queues, and/or LinkedList which can be generic?
