考虑下面的代码:

DummyBean dum = new DummyBean();
dum.setDummy("foo");
System.out.println(dum.getDummy()); // prints 'foo'

DummyBean dumtwo = dum;
System.out.println(dumtwo.getDummy()); // prints 'foo'

dum.setDummy("bar");
System.out.println(dumtwo.getDummy()); // prints 'bar' but it should print 'foo'

所以,我想把dumm复制到dum2,在不影响dum2的情况下改变dumm。但是上面的代码并没有这样做。当我改变了dumm中的一些东西,同样的变化也会发生在dum2中。

我想,当我说dumtwo = dum时,Java只复制了引用。那么,有没有办法创建一个新的dum副本并将其分配给dumtwo呢?


当前回答

是的,您只是对对象进行了引用。如果对象实现了可克隆,则可以克隆该对象。

查看这篇关于复制对象的wiki文章。

参考这里:对象复制

其他回答

请按照以下步骤进行:

public class Deletable implements Cloneable{

    private String str;
    public Deletable(){
    }
    public void setStr(String str){
        this.str = str;
    }
    public void display(){
        System.out.println("The String is "+str);
    }
    protected Object clone() throws CloneNotSupportedException {
        return super.clone();
    }
}

无论你想要得到另一个对象,简单地执行克隆。 例句:

Deletable del = new Deletable();
Deletable delTemp = (Deletable ) del.clone(); // this line will return you an independent
                                 // object, the changes made to this object will
                                 // not be reflected to other object
public class MyClass implements Cloneable {

private boolean myField= false;
// and other fields or objects

public MyClass (){}

@Override
public MyClass clone() throws CloneNotSupportedException {
   try
   {
       MyClass clonedMyClass = (MyClass)super.clone();
       // if you have custom object, then you need create a new one in here
       return clonedMyClass ;
   } catch (CloneNotSupportedException e) {
       e.printStackTrace();
       return new MyClass();
   }

  }
}

在你的代码中:

MyClass myClass = new MyClass();
// do some work with this object
MyClass clonedMyClass = myClass.clone();

你可以从http://x-stream.github.io/:用XStream自动深度复制

XStream是一个简单的库,用于将对象序列化为XML和反向 一次。

将其添加到项目中(如果使用maven)

<dependency>
    <groupId>com.thoughtworks.xstream</groupId>
    <artifactId>xstream</artifactId>
    <version>1.3.1</version>                
</dependency>

Then

DummyBean dum = new DummyBean();
dum.setDummy("foo");
DummyBean dumCopy = (DummyBean) XSTREAM.fromXML(XSTREAM.toXML(dum));

这样你就有了一个副本,而不需要实现任何克隆接口。

深度克隆是您的答案,它需要实现Cloneable接口并重写clone()方法。

public class DummyBean implements Cloneable {

   private String dummy;

   public void setDummy(String dummy) {
      this.dummy = dummy;
   }

   public String getDummy() {
      return dummy;
   }

   @Override
   public Object clone() throws CloneNotSupportedException {
      DummyBean cloned = (DummyBean)super.clone();
      cloned.setDummy(cloned.getDummy());
      // the above is applicable in case of primitive member types like String 
      // however, in case of non primitive types
      // cloned.setNonPrimitiveType(cloned.getNonPrimitiveType().clone());
      return cloned;
   }
}

你会这样称呼它 DummyBean dumtwo = dumm .clone();

class DB {
  private String dummy;

  public DB(DB one) {
    this.dummy = one.dummy; 
  }
}