Some sort algorithms (java)

sort.java

import java.util.Random;

class sort{
	public static void main(String[] a){
		Sorter[] list = {new InsertionSort(), new BubbleSort(), new QuickSort()};
		
		for(int i = 0; i < list.length; i++){
			sort.perform(list[i]);
		}
	}
	
	private static Random generator = new Random();
	
	private static void perform(Sorter s){
		int[] list = new int[1000];
		for(int i = 0; i < list.length; i++){
			list[i] = sort.generator.nextInt();
		}
		list = s.sort(list);
		
		boolean valid = true;
		for(int i = 1; i < list.length; i++){
			if(list[i-1] > list[i]){
				valid = false;
				break;
			}
		}
		
		System.out.println(s + " sort " + (valid ? "succeeded" : "failed") +"!");
	}
}

abstract class Sorter{
	public abstract int[] sort(int[] list);
}

class InsertionSort extends Sorter{
	public int[] sort(int[] list){
		int cur, j;
		for(int i = 1; i < list.length; i++){
			cur = list[i];
			for(j = i; j > 0 && list[j-1] > cur; j--){
				list[j] = list[j-1];
			}
			list[j] = cur;
		}
		
		return list;
	}
	
	public String toString(){ return "Insertion"; };
}

class BubbleSort extends Sorter{
	public int[] sort(int[] list){
		for(int i = 0; i < list.length; i++){
			for(int j = i+1; j < list.length; j++){
				if(list[i] > list[j]){
					int tmp = list[i];
					list[i] = list[j];
					list[j] = tmp;
				}
			}
		}
		return list;
	}
	
	public String toString(){ return "Bubble"; };
}

class QuickSort extends Sorter{
	public int[] sort(int[] list){
		return this.sort(list, list.length);
	}
	public int[] sort(int[] list, int l){
		if(l == 0) return new int[0];
		if(l == 1) return list;
		int pivot = list[--l];
		int[] left = new int[l];
		int[] right = new int[l];
		
		int leftLength, rightLength = leftLength = 0;
		
		for(int i = 0; i < l; i++){
			if(list[i] < pivot) left[leftLength++] = list[i];
			else right[rightLength++] = list[i];
		}
		
		left = this.sort(left, leftLength);
		right = this.sort(right, rightLength);
		
		for(int i = 0; i < leftLength; i++) list[i] = left[i];
		list[leftLength] = pivot;
		for(int i = 0; i < rightLength; i++) list[i + leftLength + 1] = right[i];
		
		return list;
	}
	
	public String toString(){ return "Quick"; };
}