Hash存储与内存泄漏

 

public class Point {
	private int x;
	private int y;
	
	
	public Point(int x, int y) {
		this.x = x;
		this.y = y;
	}

	
	@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 int getX() {
		return x;
	}
	public void setX(int x) {
		this.x = x;
	}
	public int getY() {
		return y;
	}
	public void setY(int y) {
		this.y = y;
	}
	
	

}

 

public class Test {

	public static void main(String[] args) {
		Collection<Point> aCol = new ArrayList<Point>();
		Collection<Point> hCol = new HashSet<Point>();
		
		Point a = new Point(1, 2);
		Point b = new Point(2, 2);
		Point c = new Point(1, 2);
		
		aCol.add(a);
		aCol.add(b);
		aCol.add(c);
		aCol.add(a);	//重复添加a对象
		
		hCol.add(a);
		hCol.add(b);
		hCol.add(c);
		hCol.add(a);	//重复添加a对象
		
		System.out.println(aCol.size());	//采用非hash存储，没有必要修改hashcode 和 equals方法 size不会变
		System.out.println(hCol.size());	//前：3 	 后：2	(必须同时修改hashCode()和equals())
		
		System.out.println("-----------------------");
		
		methodTest();
		
	}

	private static void methodTest() {
		Collection<Point> aCol = new ArrayList<Point>();
		Collection<Point> hCol = new HashSet<Point>();
		
		Point a = new Point(1, 2);
		Point b = new Point(2, 2);
		Point c = new Point(1, 2);
		
		aCol.add(a);
		aCol.add(b);
		aCol.add(c);
		aCol.add(a);	//重复添加a对象
		
		hCol.add(a);
		hCol.add(b);
		hCol.add(c);
		hCol.add(a);	//重复添加a对象
		
		b.setX(8);
		aCol.remove(b);
		hCol.remove(b);
		
		System.out.println(aCol.size());
		System.out.println(hCol.size());	
		//前：1 	 后：2(修改了对象的参与hash值计算的属性值   结果会导致remove不到此对象)
		//了解Hash的存储方式	
		//上面总结下来就是一个内存泄漏的实例
		
	}

}