java编程思想_005别名现象

package wzs.test2;

//将一个对象赋值给另一个对象，实际是将引用从一个地方复制到另一个地方
//这意味着，如果对象tank1=tank2，那么tank1和tank2都指向原本只有tank2指向的那个对象
//为了避免这种问题，应该tank1.level=tank2.level
public class Test_wzs2
{
    public static void main(String[] args)
    {
        Tank tank1 = new Tank();
        Tank tank2 = new Tank();

        tank1.level = 1;
        tank2.level = 2;
        System.out.println("tank1.level=" + tank1.level + ", tank2.level=" + tank2.level);

        tank1 = tank2;
        System.out.println("tank1.level=" + tank1.level + ", tank2.level=" + tank2.level);

        tank1.level = 5;
        System.out.println("tank1.level=" + tank1.level + ", tank2.level=" + tank2.level);

        tank2.level = 7;
        System.out.println("tank1.level=" + tank1.level + ", tank2.level=" + tank2.level);
        // ----------------------------
        Tank tank3 = new Tank();
        Tank tank4 = new Tank();
        tank3.level = 1;
        tank4.level = 2;
        tank3.level = tank4.level;
        System.out.println("\ntank3.level=" + tank3.level + ", tank4.level=" + tank4.level);

        tank3.level = 7;
        tank4.level = 8;
        System.out.println("tank3.level=" + tank3.level + ", tank4.level=" + tank4.level);
    }
}

class Tank
{
    int level;
}

输出结果:

tank1.level=1, tank2.level=2
tank1.level=2, tank2.level=2
tank1.level=5, tank2.level=5
tank1.level=7, tank2.level=7

tank3.level=2, tank4.level=2
tank3.level=7, tank4.level=8