java数组浅拷贝陷阱Shallow Clone

 

package testpro;

import java.util.Arrays;

/**
 * 数组的浅拷贝陷阱
 *
 */
public class ArrayDilatation {
	public static void main(String[] args) {
		Ball[] balls = new Ball[6];
		System.out.println("------------balls------------"+balls);
		for(int i=0;i<balls.length;i++) {
			balls[i] = new Ball(i, Color.values()[i]);
			System.out.println("balls1:"+balls[i]);
		}
		Ball[] balls2 = dilatationArray(balls, balls.length);
		balls2[5].setColor(Color.blue);
		System.out.println("------------balls2------------"+balls2);
		for (Ball ball : balls2) {
			System.out.println("balls2:"+ball);
		}
		System.out.println("------------balls------------"+balls);
		for (Ball ball : balls) {
			System.out.println("balls1:"+ball);
		}
		
	}
	public static <T> T[] dilatationArray(T[] datas,int newlen) {
		//不能为负数
		newlen = newlen<0?0:newlen;
		//生成一个新数组，并copy原值到新数组
		return Arrays.copyOf(datas, newlen);
	}
}

enum Color{
	red,orange,yellow,green,blue,whilt;
}

class Ball{
	private int id;
	private Color color;
	public Ball(int id,Color color) {
		this.id = id;
		this.color = color;
	}
	
	public int getId() {
		return id;
	}

	public void setId(int id) {
		this.id = id;
	}

	public Color getColor() {
		return color;
	}

	public void setColor(Color color) {
		this.color = color;
	}

	@Override
	public String toString() {
		return "Ball [编号=" + id + ", 颜色=" + color + "]";
	}
	
}

代码运行结果如下：

------------balls------------[Ltestpro.Ball;@7852e922
balls1:Ball [编号=0, 颜色=red]
balls1:Ball [编号=1, 颜色=orange]
balls1:Ball [编号=2, 颜色=yellow]
balls1:Ball [编号=3, 颜色=green]
balls1:Ball [编号=4, 颜色=blue]
balls1:Ball [编号=5, 颜色=whilt]
------------balls2------------[Ltestpro.Ball;@4e25154f
balls2:Ball [编号=0, 颜色=red]
balls2:Ball [编号=1, 颜色=orange]
balls2:Ball [编号=2, 颜色=yellow]
balls2:Ball [编号=3, 颜色=green]
balls2:Ball [编号=4, 颜色=blue]
balls2:Ball [编号=5, 颜色=blue]
------------balls------------[Ltestpro.Ball;@7852e922
balls1:Ball [编号=0, 颜色=red]
balls1:Ball [编号=1, 颜色=orange]
balls1:Ball [编号=2, 颜色=yellow]
balls1:Ball [编号=3, 颜色=green]
balls1:Ball [编号=4, 颜色=blue]
balls1:Ball [编号=5, 颜色=blue]

很明显，改变了balls2这一个数组，结果balls中也跟着被修改了，而且对象引用得地址值也不一样，这种情况就是典型的浅拷贝，用着方便，但是有坑，有风险；为了避免出现这样的情况，我们应该遍历取出balls中的元素，重新生成一个Ball对象然后赋值给balls2中的元素即可；

数组的copyof方法是一个浅拷贝，与序列化的浅拷贝一样：基本类型是直接拷贝值，其他都是拷贝引用地址。数组的clone方法，集合的clone方法也都是浅拷贝，需要特别留意，不要为了少些代码给自己挖坑。