CloneNotSupportedException的解决方案 + Object的clone方法分析

青旅半醒 2024-02-05 20:56 20阅读 0赞

### CloneNotSupportedException的解决方案 ###

#### 引入问题： ####

在一次测试clone方法时，D类Override了Object类的clone方法

public class D {
        
    
        private Integer A1;
        private Integer A2;
    
        public D() {
        
        }
    
        public D(Integer a1, Integer a2 {
        
            A1 = a1;
            A2 = a2;
        }
    
        @Override
        protected Object clone() throws CloneNotSupportedException {
        
            return super.clone();
        }
    }
    123456789101112131415161718

在测试类中执行clone方法报错了

public class Test5 {
        
    
        public static void main(String[] args) {
        
    
            D p  = new D();
            D p2 = null;
            try {
        
                p2 = (D)p.clone();
            } catch (CloneNotSupportedException e) {
        
                e.printStackTrace();
            }
            System.out.println(p == p2);
    
        }
    
    }
    12345678910111213141516

![在这里插入图片描述][d89d0ae9e01c4d2ca9aba003e74a2fe4.png_pic_center]

抛出了 CloneNotSupportedException

#### 寻找原因： ####

既然是重写自Object的clone方法，那么去看看Object对该方法的定义：

protected native Object clone() throws CloneNotSupportedException;
    1

其中对于异常抛出的描述如下：

Throws:  
CloneNotSupportedException – if the object’s class does not support the [Cloneable][] interface. Subclasses that override the clone method can also throw this exception to indicate that an instance cannot be cloned.

如果对象的class不实现Cloneable接口，子类重写clone方法会同样抛出异常表示实例不能被克隆；

哦？

那不意思就是说：你要不父类实现Cloneable接口，要不就子类实现Cloneable

两个测试代码：

测试1： 在父类上实现Cloneable接口

public class TestClone {
        
    
        public static void main(String[] args) throws CloneNotSupportedException {
        
            Father father = new Father();
            Father fatherClone = (Father) father.clone();
    
            Son son = new Son();
            Son sonClone = (Son) son.clone();
    
            System.out.println(father==fatherClone);
            System.out.println(son==sonClone);
    
        }
    
    }
    
    class Father implements Cloneable{
        
        private Integer f1;
        private Integer f2;
    
        public Father() {
        
        }
    
        public Father(Integer f1, Integer f2) {
        
            this.f1 = f1;
            this.f2 = f2;
        }
    
        @Override
        protected Object clone() throws CloneNotSupportedException {
        
            return super.clone();
        }
    }
    
    
    class Son extends Father{
        
        private Integer s1;
        private Integer s2;
    
        public Son() {
        
        }
    
        public Son(Integer s1, Integer s2) {
        
            this.s1 = s1;
            this.s2 = s2;
        }
    
        @Override
        protected Object clone() throws CloneNotSupportedException {
        
            return super.clone();
        }
    }
    12345678910111213141516171819202122232425262728293031323334353637383940414243444546474849505152

不出意外，没有任何问题

![在这里插入图片描述][ade1b384ddcc428f9538a58f0bc5c91f.png_pic_center]

测试2：在子类上实现Cloneable接口

public class TestClone {
        
    
        public static void main(String[] args) throws CloneNotSupportedException {
        
    //        Father father = new Father();
    //        Father fatherClone = (Father) father.clone();
    
            Son son = new Son();
            Son sonClone = (Son) son.clone();
    
    //        System.out.println(father==fatherClone);
            System.out.println(son==sonClone);
    
        }
    
    }
    
    class Father {
        
        private Integer f1;
        private Integer f2;
    
        public Father() {
        
        }
    
        public Father(Integer f1, Integer f2) {
        
            this.f1 = f1;
            this.f2 = f2;
        }
    
        @Override
        protected Object clone() throws CloneNotSupportedException {
        
            return super.clone();
        }
    }
    
    
    class Son extends Father implements Cloneable{
        
        private Integer s1;
        private Integer s2;
    
        public Son() {
        
        }
    
        public Son(Integer s1, Integer s2) {
        
            this.s1 = s1;
            this.s2 = s2;
        }
    
        @Override
        protected Object clone() throws CloneNotSupportedException {
        
            return super.clone();
        }
    }
    12345678910111213141516171819202122232425262728293031323334353637383940414243444546474849505152

执行父类的clone报错，但是执行子类的clone没得问题

![在这里插入图片描述][e20707aacf6542c5b5d8ebbc5dda93fe.png_pic_center]

#### SO： ####

**哪个类的需要clone，就在那个类在重写clone方法，并且在那个类或者其父类中实现Cloneable接口**

### 详细分析clone方法的实现： ###

由于Object的clone方法是native修饰的，也就是虚拟机内部实现的方法

根据[Hotspot][]虚拟机定义，找到Object.c

![在这里插入图片描述][d9b10c7afdbc4fd8aaabb4e0b5e253b5.png_pic_center]

#### 为什么要实现Cloneable接口？ ####

在JVM\_Clone方法中有这样一段判断：

![在这里插入图片描述][95b078d8d7924f8d97730fd68b073bc2.png_pic_center]

很明显，虚拟机给你抛出的异常

#### 为什么会出现地址不同的情况？ ####

![在这里插入图片描述][08c973028d8a4f80927884eebfd4bb10.png_pic_center]

很明显，直接在[堆内存][Link 1]中执行allocate方法开辟新的对象空间

并返回一个 oop 对象，也就是对象描述的指针（指向对象的首地址）

[d89d0ae9e01c4d2ca9aba003e74a2fe4.png_pic_center]: https://image.dandelioncloud.cn/pgy_files/images/2024/01/30/418bc0fcc57748efb8482d1c0df2eb37.png
[Cloneable]: https://so.csdn.net/so/search?q=Cloneable&spm=1001.2101.3001.7020
[ade1b384ddcc428f9538a58f0bc5c91f.png_pic_center]: https://image.dandelioncloud.cn/pgy_files/images/2024/01/30/c1dc89ddcd604e529293877932be60e2.png
[e20707aacf6542c5b5d8ebbc5dda93fe.png_pic_center]: https://image.dandelioncloud.cn/pgy_files/images/2024/01/30/b8e23c1f765747468f8da6e586de6949.png
[Hotspot]: https://so.csdn.net/so/search?q=Hotspot&spm=1001.2101.3001.7020
[d9b10c7afdbc4fd8aaabb4e0b5e253b5.png_pic_center]: https://image.dandelioncloud.cn/pgy_files/images/2024/01/30/57fa5a5f0f6a4e918a4f111a6d13df7a.png
[95b078d8d7924f8d97730fd68b073bc2.png_pic_center]: https://image.dandelioncloud.cn/pgy_files/images/2024/01/30/1b5098951a2b4469a91edc632a10b648.png
[08c973028d8a4f80927884eebfd4bb10.png_pic_center]: https://image.dandelioncloud.cn/pgy_files/images/2024/01/30/e540d0142caf48e7b815d721a8394b69.png
[Link 1]: https://so.csdn.net/so/search?q=%E5%A0%86%E5%86%85%E5%AD%98&spm=1001.2101.3001.7020