Quicksort in java

gistfile1.txt

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package sorts;

import java.io.PrintStream;
import java.util.ArrayList;

/**
 *
 * @author Ethan
 */
public class Sorts {

    private static ArrayList<Integer> list = new ArrayList<Integer>();
    private static PrintStream out = System.out;
    public static void main(String[] args) {
        list.add(0);
        list.add(-3);
        list.add(7);
        list.add(10);
        list.add(4);
        list.add(5);
        
        list = quicksort(list);
        for(int i = 0; i < list.size(); ++i)
        {
            out.print(", " + list.get(i));
        }
    }

 
    
    private static ArrayList<Integer> quicksort(ArrayList<Integer> input){
  	
		if(input.size() <= 1){
			return input;
		}
		
		int middle = (int) Math.ceil((double)input.size() / 2);
		Integer pivot = input.get(middle);
 
		ArrayList<Integer> less = new ArrayList<Integer>();
		ArrayList<Integer> greater = new ArrayList<Integer>();
		
		for (int i = 0; i < input.size(); i++) {
			if(pivot.compareTo(input.get(i)) >= 0){
				if(i == middle){
					continue;
				}
				less.add(input.get(i));
			}
			else{
				greater.add(input.get(i));
			}
		}
		
		return concatenate(quicksort(less), pivot, quicksort(greater));
	}
    
    private static ArrayList<Integer> concatenate(ArrayList<Integer> less, Integer pivot, ArrayList<Integer> greater){
		
		ArrayList<Integer> list = new ArrayList<Integer>();
		
		for (int i = 0; i < less.size(); i++) {
			list.add(less.get(i));
		}
		
		list.add(pivot);
		
		for (int i = 0; i < greater.size(); i++) {
			list.add(greater.get(i));
		}
		
		return list;
	}
}