Java中的clone()和Cloneable接口使用方法是什么

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clone()和Cloneable接口

clone顾名思义就是克隆，即，复制一个相等的对象，但是不同的引用地址。

我们知道拿到一个对象的地址，只要提供相应的方法就可以修改这个对象，但是如果我们想要得到这个对象去修改它，又想保留这个对象原来的属性，这是就可以使用clone()，它会复制一个内容相同的对象而具有不同内存地址。

Cloneable接口，就是我们要使用clone()必须实现的接口，不然会抛出异常。

public class Bean implements Cloneable {    private String a;     public Bean(String a) {        this.a = a;    }     public String getA() {        return a;    }     @Override    protected Object clone() throws CloneNotSupportedException {        return super.clone();    }     @Override    public boolean equals(Object o) {        if(o instanceof Bean){            Bean bean = (Bean) o;            return bean.getA().equals(a);        }        return false;    }}

在Cloneable 接口中并没有给我们定义任何方法

这里需要重写clone()方法

protected native Object clone() throws CloneNotSupportedException;protected Object clone() throws CloneNotSupportedException {        if (!(this instanceof Cloneable)) {            throw new CloneNotSupportedException("Class " + getClass().getName() +                                                 " doesn't implement Cloneable");        }         return internalClone();    }

它是Object类里面的native方法，它是protected的，根据需要可以写为public，可以看到如果不实现Cloneable接口将会抛出CloneNotSupportedException 异常。

测试一下

try {             Bean a = new Bean("lzy");            Bean b = a;            Bean c = (Bean) a.clone();             Log.i(TAG, "onCreate: " + (a == b));         //true            Log.i(TAG, "onCreate: " + (a.equals(b)));    //true             Log.i(TAG, "onCreate: " + (a == c));         //false            Log.i(TAG, "onCreate: " + (a.equals(c)));    //true          } catch (CloneNotSupportedException e) {            e.printStackTrace();        }

可以看到克隆出来的类的地址是不同的，而内容是相同的。

下面修改一下，在Bean加一个成员变量ChildBean

public class ChildBean implements Cloneable {    private String c;    public String getC() {        return c;    }    public ChildBean(String c) {        this.c = c;    }    @Override    public Object clone() throws CloneNotSupportedException {        return super.clone();    }    @Override    public boolean equals(Object o) {        if (o instanceof ChildBean) {            ChildBean bean = (ChildBean) o;            return bean.getC().equals(c);        }        return false;    }}

public class Bean implements Cloneable {    private String a;    private ChildBean childBean;     public Bean(String a, ChildBean childBean) {        this.a = a;        this.childBean = childBean;    }    public String getA() {        return a;    }     public ChildBean getChildBean() {        return childBean;    }     @Override    public Object clone() throws CloneNotSupportedException {        return super.clone();    }     @Override    public boolean equals(Object o) {        if (o instanceof Bean) {            Bean bean = (Bean) o;            return bean.getA().equals(a);        }        return false;    }}

Bean a = new Bean("lzy", new ChildBean("child"));            Bean b = a;            Bean c = (Bean) a.clone();             Log.i(TAG, "onCreate: " + (a.getChildBean() == b.getChildBean()));         //true            Log.i(TAG, "onCreate: " + (a.getChildBean().equals(b.getChildBean())));    //true             Log.i(TAG, "onCreate: " + (a.getChildBean() == c.getChildBean()));         //true            Log.i(TAG, "onCreate: " + (a.getChildBean().equals(c.getChildBean())));    //true

测试发现有一个结果不是我们所预期的，这意味着并没有真正克隆ChildBean，只是克隆的它的内存地址，导致两个具有相同的内存地址，这也就是浅克隆，此时我们需要的是深克隆，需要按照下面方法修改，重写clone()方法

  @Override    public Object clone() throws CloneNotSupportedException {        Bean bean = (Bean) super.clone();        bean.childBean = (ChildBean) bean.childBean.clone();        return bean;    }

但是这样做如果有很多层的类，那每一层都需要去重写，显得很麻烦。所以我们可以用下面的工具类来实现

public class BeanUtil {    public static  T cloneTo(T src) throws RuntimeException {        ByteArrayOutputStream memoryBuffer = new ByteArrayOutputStream();        ObjectOutputStream out = null;        ObjectInputStream in = null;        T dist = null;        try {            out = new ObjectOutputStream(memoryBuffer);            out.writeObject(src);            out.flush();            in = new ObjectInputStream(new ByteArrayInputStream(memoryBuffer.toByteArray()));            dist = (T) in.readObject();        } catch (Exception e) {            throw new RuntimeException(e);        } finally {            if (out != null)                try {                    out.close();                    out = null;                } catch (IOException e) {                    throw new RuntimeException(e);                }            if (in != null)                try {                    in.close();                    in = null;                } catch (IOException e) {                    throw new RuntimeException(e);                }        }        return dist;    }}

Bean a = new Bean("lzy", new ChildBean("child"));        Bean b = BeanUtil.cloneTo(a);         Log.i(TAG, "onCreate: " + (a.getChildBean() == b.getChildBean()));         //false        Log.i(TAG, "onCreate: " + (a.getChildBean().equals(b.getChildBean())));    //true

这样就可以很轻松的得到我们预期的结果，但是记得每一个类都要去 实现Serializable接口。

Cloneable和clone()的总结

1.Cloneable 的用途

Cloneable和Serializable一样都是标记型接口，它们内部都没有方法和属性，implements Cloneable表示该对象能被克隆，能使用Object.clone()方法。如果没有implements Cloneable的类调用Object.clone()方法就会抛出CloneNotSupportedException。

2.克隆的分类

(1)浅克隆（shallow clone），浅拷贝是指拷贝对象时仅仅拷贝对象本身和对象中的基本变量，而不拷贝对象包含的引用指向的对象。

(2)深克隆（deep clone），深拷贝不仅拷贝对象本身，而且拷贝对象包含的引用指向的所有对象。

举例区别一下：对象A1中包含对B1的引用，B1中包含对C1的引用。浅拷贝A1得到A2，A2中依然包含对B1的引用，B1中依然包含对C1的引用。深拷贝则是对浅拷贝的递归，深拷贝A1得到A2，A2中包含对B2（B1的copy）的引用，B2中包含对C2（C1的copy）的引用。

3.克隆的举例

要让一个对象进行克隆，其实就是两个步骤：

1.让该类实现java.lang.Cloneable接口；

2.重写（override）Object类的clone()方法。

public class Wife implements Cloneable {      private int id;      private String name;      public int getId() {          return id;      }      public void setId(int id) {          this.id = id;      }      public String getName() {          return name;      }      public void setName(String name) {          this.name = name;      }      public Wife(int id,String name) {          this.id = id;          this.name = name;      }      @Override      public int hashCode() {//myeclipse自动生成的          final int prime = 31;          int result = 1;          result = prime * result + id;          result = prime * result + ((name == null) ? 0 : name.hashCode());          return result;      }      @Override      public boolean equals(Object obj) {//myeclipse自动生成的          if (this == obj)              return true;          if (obj == null)              return false;          if (getClass() != obj.getClass())              return false;          Wife other = (Wife) obj;          if (id != other.id)              return false;          if (name == null) {              if (other.name != null)                  return false;          } else if (!name.equals(other.name))              return false;          return true;      }      @Override      public Object clone() throws CloneNotSupportedException {          return super.clone();      }      /**      * @param args      * @throws CloneNotSupportedException       */      public static void main(String[] args) throws CloneNotSupportedException {          Wife wife = new Wife(1,"wang");          Wife wife2 = null;          wife2 = (Wife) wife.clone();          System.out.println("class same="+(wife.getClass()==wife2.getClass()));//true          System.out.println("object same="+(wife==wife2));//false          System.out.println("object equals="+(wife.equals(wife2)));//true      }  }

4.浅克隆的举例

public class Husband implements Cloneable {      private int id;      private Wife wife;      public Wife getWife() {          return wife;      }      public void setWife(Wife wife) {          this.wife = wife;      }      public int getId() {          return id;      }      public void setId(int id) {          this.id = id;      }      public Husband(int id) {          this.id = id;      }      @Override      public int hashCode() {//myeclipse自动生成的          final int prime = 31;          int result = 1;          result = prime * result + id;          return result;      }      @Override      protected Object clone() throws CloneNotSupportedException {          return super.clone();      }      @Override      public boolean equals(Object obj) {//myeclipse自动生成的          if (this == obj)              return true;          if (obj == null)              return false;          if (getClass() != obj.getClass())              return false;          Husband other = (Husband) obj;          if (id != other.id)              return false;          return true;      }      /**      * @param args      * @throws CloneNotSupportedException       */      public static void main(String[] args) throws CloneNotSupportedException {          Wife wife = new Wife(1,"jin");          Husband husband = new Husband(1);          Husband husband2 = null;          husband.setWife(wife);          husband2 = (Husband) husband.clone();          System.out.println("husband class same="+(husband.getClass()==husband2.getClass()));//true          System.out.println("husband object same="+(husband==husband2));//false          System.out.println("husband object equals="+(husband.equals(husband)));//true          System.out.println("wife class same="+(husband.getWife().getClass()==husband2.getWife().getClass()));//true          System.out.println("wife object same="+(husband.getWife()==husband2.getWife()));//true          System.out.println("wife object equals="+(husband.getWife().equals(husband.getWife())));//true      }  }

5.深克隆的举例

如果要深克隆，需要重写（override）Object类的clone()方法，并且在方法内部调用持有对象的clone()方法；注意如下代码的clone()方法

public class Husband implements Cloneable {      private int id;      private Wife wife;      public Wife getWife() {          return wife;      }      public void setWife(Wife wife) {          this.wife = wife;      }      public int getId() {          return id;      }      public void setId(int id) {          this.id = id;      }      public Husband(int id) {          this.id = id;      }      @Override      public int hashCode() {//myeclipse自动生成的          final int prime = 31;          int result = 1;          result = prime * result + id;          return result;      }      @Override      protected Object clone() throws CloneNotSupportedException {          Husband husband = (Husband) super.clone();          husband.wife = (Wife) husband.getWife().clone();          return husband;      }      @Override      public boolean equals(Object obj) {//myeclipse自动生成的          if (this == obj)              return true;          if (obj == null)              return false;          if (getClass() != obj.getClass())              return false;          Husband other = (Husband) obj;          if (id != other.id)              return false;          return true;      }      /**      * @param args      * @throws CloneNotSupportedException       */      public static void main(String[] args) throws CloneNotSupportedException {          Wife wife = new Wife(1,"jin");          Husband husband = new Husband(1);          Husband husband2 = null;          husband.setWife(wife);          husband2 = (Husband) husband.clone();          System.out.println("husband class same="+(husband.getClass()==husband2.getClass()));//true          System.out.println("husband object same="+(husband==husband2));//false          System.out.println("husband object equals="+(husband.equals(husband)));//true          System.out.println("wife class same="+(husband.getWife().getClass()==husband2.getWife().getClass()));//true          System.out.println("wife object same="+(husband.getWife()==husband2.getWife()));//false          System.out.println("wife object equals="+(husband.getWife().equals(husband.getWife())));//true      }  }

但是也有不足之处，如果Husband内有N个对象属性，突然改变了类的结构，还要重新修改clone()方法。

解决办法：可以使用Serializable运用反序列化手段，调用java.io.ObjectInputStream对象的 readObject()方法。

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