I'm trying to figure out why I'm getting a NullPointerException despite the fact that the array is populated with card object. What I'm asking is that can my QuickSort algorithm use the compare method I override in my card class?
QuickSort:
package sort;
//All import goes here
import java.util.ArrayList;
import java.util.Comparator;
//Comment out at the moment
//import java.util.List;
public class QuickSort<T> {
private ArrayList<T> list;
private int length;
Comparator<T> pod;
public void sort(ArrayList<T> lst){
//Check if the list is empty
//if(lst.isEmpty() || lst == null){
if(lst == null || lst.isEmpty()){
return;
}
this.list = lst;
length = lst.size();
quickSort(0, length - 1);
}
private void quickSort(int lowIndex, int highIndex){
int low = lowIndex;
int high = highIndex;
//Find the pivot value
T pivot = list.get(lowIndex + (highIndex - lowIndex)/2);
while(low <= high){
/**
* In each iteration, we will find a value from the left side
* which is greater than the pivot value, and also we will
* find a value from the right side which is less then the pivot
* once the search is done, we will then exchange both numbers
*/
//o1 < pivot
while(pod.compare(list.get(low), pivot) == -1){
low++;
}
//o1 > pivot
while(pod.compare(list.get(high), pivot) == 1){
high--;
}
if(low <= high){
swap(low, high);
//Move index to next position on both side
low++;
high--;
}
}
//Call quickSort recursively
if(lowIndex < high){
quickSort(lowIndex, high);
}
if(low < highIndex){
quickSort(low, highIndex);
}
}
private void swap(int i, int j){
//Temporary variable to hold the element at index i
T temp = list.get(i);
//Swap i index with the element in j index
list.set(i, list.get(j));
//Swap j index with the element that was in i index
list.set(j, temp);
}
}
Card:
//Compare method in my Card class
public class Card implements Comparator<Card>{
.....
@Override
public int compare(Card o1, Card o2) {
//Check if o1 has the highest suit
if(o1.getSuit().getVal() > o2.getSuit().getVal()){
return 1;
}
//Check if o2 has highest suit
else if(o1.getSuit().getVal() < o2.getSuit().getVal()){
return -1;
}
//Check if the suit are the same
else if(o1.getSuit().equals(o2.getSuit())){
//Check if o1 has the highest value
if(o1.getValue().getVal() > o2.getValue().getVal()){
return 1;
}
//Check if o2 has the highest value
else if(o1.getValue().getVal() > o2.getValue().getVal()){
return -1;
}
}
//Either there duplicate or something wrong with the compare method.
System.out.println("Well there something wrong with the card Compare method or there duplicate of card in the deck.");
return 0;
}
}
Spade:
//Sort player hand for easy readability
QuickSort<Card> sort = new QuickSort<Card>();
System.out.println(USER.getHand().size());
sort.sort(USER.getHand());
Error:
Exception in thread "main" java.lang.NullPointerException
at sort.QuickSort.quickSort(QuickSort.java:48)
at sort.QuickSort.sort(QuickSort.java:28)
at Spade.main(Spade.java:155)
Update:
I check if the argument were null for the compare method where the exception originate, both argument check return false.
