賦值操作後，對象的引用發生變化

// 此用例來源於Thinking in java 

class Tank{

int level;

String msg;

Tmp tmp;

@Override

public String toString() {

return "level = "+level+" msg="+msg+" tmp="+tmp;

}

}

class Tmp{

private String name;

public Tmp(String name){

this.name=name;

}

@Override

public String toString() {

return this.name;

}

}

-----------------

Tank t1 = new Tank();

t1.level =1;

t1.msg="message 1";

t1.tmp = new Tmp("tmp 1");

System.out.println(t1);

Tank t2 = new Tank();

t2.level =2;

t2.msg="message 2";

t2.tmp = new Tmp("tmp 2");

System.out.println(t2);

t1 = t2 ;

t2賦值給t1後，t2中原對象的引用也指向了t1對象的引用，原先t2對象的引用被覆蓋，信息丟失。
此時t2與t1指向同一個引用。