原型模式(克隆模式)—浅谈浅克隆与深克隆

Posted 2020-09-20 码农皮邱

克隆是什么？它的产生背景？

当new的对象是多例的时候，new对象将会不断占据内存。特别是消耗内存的大对象，比如数据库连接等。平时运用的不多，只在spring等容器有见过，此处不多赘述，了解即可。

浅克隆与深克隆是什么意思？通过案例逐步探讨。

public class Star implements Cloneable,Serializable{
    private String name;
    private Date birthday;
</span><span style="color: #0000ff;">public</span><span style="color: #000000;"> Star(){}
</span><span style="color: #0000ff;">public</span><span style="color: #000000;"> Star(String name, Date birthday) {
    </span><span style="color: #0000ff;">super</span><span style="color: #000000;">();
    </span><span style="color: #0000ff;">this</span>.name =<span style="color: #000000;"> name;
    </span><span style="color: #0000ff;">this</span>.birthday =<span style="color: #000000;"> birthday;
}

</span><span style="color: #008000;">//</span><span style="color: #008000;">实现浅克隆</span>

    @Override

protected Object clone() throws CloneNotSupportedException {

return super.clone();

}
</span><span style="color: #0000ff;">public</span><span style="color: #000000;"> String getName() {
    </span><span style="color: #0000ff;">return</span><span style="color: #000000;"> name;
}
</span><span style="color: #0000ff;">public</span> <span style="color: #0000ff;">void</span><span style="color: #000000;"> setName(String name) {
    </span><span style="color: #0000ff;">this</span>.name =<span style="color: #000000;"> name;
}
</span><span style="color: #0000ff;">public</span><span style="color: #000000;"> Date getBirthday() {
    </span><span style="color: #0000ff;">return</span><span style="color: #000000;"> birthday;
}
</span><span style="color: #0000ff;">public</span> <span style="color: #0000ff;">void</span><span style="color: #000000;"> setBirthday(Date birthday) {
    </span><span style="color: #0000ff;">this</span>.birthday =<span style="color: #000000;"> birthday;
}

}

明星实体类-浅克隆

 1 public class Client {
 2     public static void main(String[] args) throws CloneNotSupportedException {
 3         Date date=new Date(1346545646556465131L);
 4         //new一个明星：杨洋
 5         Star  yangYang=new Star("杨洋",date);
 6         System.out.println(yangYang);
 7         System.out.println(yangYang.getName());
 8         System.out.println(yangYang.getBirthday());
 9         
10         date.setTime(4685456456456465465L);
11         System.out.println(yangYang.getBirthday());
12         
13         //克隆杨洋:满足你当明星的梦
14         Star me=(Star) yangYang.clone();
15         System.out.println(me);
16         me.setName("周杰伦");
17         System.out.println(me.getName());
18         System.out.println(me.getBirthday());    
19     }
20 }

问题：我们发现，当date改变的时候，克隆对象的date也随之改变。这个不难理解，因为原型对象改变，克隆对象也随之改变，克隆对象只是克隆了star对象，并没有去克隆star对象中的birthday对象。

结论：浅克隆就是克隆对象直接引用原型对象。

public class Star2 implements Cloneable{
    private String name;
    private Date birthday;
</span><span style="color: #0000ff;">public</span><span style="color: #000000;"> Star2(){}
</span><span style="color: #0000ff;">public</span><span style="color: #000000;"> Star2(String name, Date birthday) {
    </span><span style="color: #0000ff;">super</span><span style="color: #000000;">();
    </span><span style="color: #0000ff;">this</span>.name =<span style="color: #000000;"> name;
    </span><span style="color: #0000ff;">this</span>.birthday =<span style="color: #000000;"> birthday;
}
</span><span style="color: #008000;">//</span><span style="color: #008000;">实现深克隆</span>

    @Override

protected Object clone() throws CloneNotSupportedException {

Object obj= super.clone();
    Star2 s</span>=<span style="color: #000000;">(Star2)obj;
    s.birthday</span>=(Date) <span style="color: #0000ff;">this</span><span style="color: #000000;">.birthday.clone();
    </span><span style="color: #0000ff;">return</span><span style="color: #000000;"> obj;
}

</span><span style="color: #0000ff;">public</span><span style="color: #000000;"> String getName() {
    </span><span style="color: #0000ff;">return</span><span style="color: #000000;"> name;
}
</span><span style="color: #0000ff;">public</span> <span style="color: #0000ff;">void</span><span style="color: #000000;"> setName(String name) {
    </span><span style="color: #0000ff;">this</span>.name =<span style="color: #000000;"> name;
}
</span><span style="color: #0000ff;">public</span><span style="color: #000000;"> Date getBirthday() {
    </span><span style="color: #0000ff;">return</span><span style="color: #000000;"> birthday;
}
</span><span style="color: #0000ff;">public</span> <span style="color: #0000ff;">void</span><span style="color: #000000;"> setBirthday(Date birthday) {
    </span><span style="color: #0000ff;">this</span>.birthday =<span style="color: #000000;"> birthday;
}

}

明星实体类-深克隆

 1 public class Client2 {
 2     public static void main(String[] args) throws CloneNotSupportedException {
 3         Date date=new Date(1346545646556465131L);
 4         //new一个明星：杨洋
 5         Star2  yangYang=new Star2("杨洋",date);
 6         Star2 me=(Star2) yangYang.clone();//深克隆里面的birthday对象是一个新对象
 7         
 8         System.out.println(yangYang);
 9         System.out.println(yangYang.getName());
10         System.out.println(yangYang.getBirthday());
11         
12         date.setTime(4685456456456465465L);
13         System.out.println(yangYang.getBirthday());
14         
15         
16         System.out.println(me);
17         me.setName("周杰伦");
18         System.out.println(me.getName());
19         System.out.println(me.getBirthday());        
20     }
21 }

 

问题：我们发现，当date改变的时候，克隆对象的bitthday并没有随之改变。通过实体类可知，当克隆对象的时候，随之也去克隆了实体类里面的引用对象，即克隆对象的birthday是一个new的对象。

结论：深克隆就是递归克隆出原型对象里的所有引用对象。