ArrayList_HashSet的比较及hashCode分析

Java隐式内存泄漏：代码用于演示如果修改Java类中的属性，会导致HashSet中元素的值后导致remove()方法失效，元素无法删除，因此在写代码时，要避免这种情况的发生。

对象类：

package cn.sunft.day01.reflect;

/**
 * 定义一个点的类,供反射测试用
 * @author sunft
 *
 */
public class ReflectPoint {
	
	private int x;
	public int y;
	public String str1 = "ball";
	public String str2 = "basketball";
	public String str3 = "itcast";
	
	
	public ReflectPoint(int x, int y) {
		super();
		this.x = x;
		this.y = y;
	}

	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;
	}
	
	@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;
		ReflectPoint other = (ReflectPoint) obj;
		if (x != other.x)
			return false;
		if (y != other.y)
			return false;
		return true;
	}

	@Override
	public String toString() {
		return str1 + ":" + str2 + ":" + str3;
	}
	
}

测试类：

package cn.sunft.day01.reflect;

import java.util.ArrayList;
import java.util.Collection;
import java.util.HashSet;

/**
 * 综合案例
 * @author sunft
 *
 */
public class ComprehensiveCase {

	public static void main(String[] args) {
		Collection list = new ArrayList();
		Collection set = new HashSet();
		
		ReflectPoint pt1 = new ReflectPoint(3, 3);
		ReflectPoint pt2 = new ReflectPoint(5, 5);
		ReflectPoint pt3 = new ReflectPoint(3, 3);
		
		list.add(pt1);
		list.add(pt2);
		list.add(pt3);
		list.add(pt1);
		
		set.add(pt1);
		set.add(pt2);
		set.add(pt3);
		set.add(pt1);
		
		//修改对象的值后,删除失败
		//修改后hash值改变,对象移除失败
		pt1.y = 7;
		set.remove(pt1);
		
		System.out.println(list.size()); 
		//HashSet默认不会保存相同的对象,因此这里打印3
		System.out.println(set.size());  //移除失败，打印3
	}

}