java 匿名内部类实现接口，运用Collections.sort()方法出错? 400 报错

java 匿名内部类实现接口，运用Collections.sort()方法出错? 400 报错

package day07;

import java.util.Collections; import java.util.Comparator; import java.util.HashSet; import java.util.Set;

public class Point { private int x, y; public Point(int x, int y){ this.x=x; this.y=y; } public void setX(int x){ this.x=x; } public void setY(int y){ this.y=y; } public int getX(){ return x; } public int getY(){ return y; } public String toString(){ return x+","+y; } public boolean equals(Point p){//重写了equals()方法，需重写hashCode()方法 if(p==null) return false; if(p==this) return true; if(p instanceof Point){ Point o=(Point) p; return this.x==o.x&&this.y==o.y; } else{ return false; } } @Override public int hashCode() { final int prime = 31; int result = 1; result = prime * result + x; result = prime * result + y; return result; } @Override public boolean equals(Object obj) { if (this == obj) return true; if (obj == null) return false; if (getClass() != obj.getClass()) return false; Point other = (Point) obj; if (x != other.x) return false; if (y != other.y) return false; return true; }

	public static void main(String[] args) {
		Set<Point> set=new HashSet<Point>();
		set.add(new Point(7, 2));
		set.add(new Point(3, 1));
		set.add(new Point(1, 9));
		System.out.println(set);
		System.out.println(set.contains(new Point(7, 2)));
		Collections.sort(set, new Comparator<Point>(){//出错！！！？
			public int compare(Point p1, Point p2){
				return (p1.x*p1.x+p1.y*p1.y)-(p2.x*p2.x+p2.y*p2.y);
			}
		});
		System.out.println(set);
		
	}

}

为什么Collentions.sort这里会出现编译错误啊？