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How do I copy an object in Java?

Asked 2009-05-15T14:30:26.943
937

Consider the code below:

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'

So, I want to copy the dum to dumtwo and change dum without affecting the dumtwo. But the code above is not doing that. When I change something in dum, the same change is happening in dumtwo also.

I guess, when I say dumtwo = dum, Java copies the reference only. So, is there any way to create a fresh copy of dum and assign it to dumtwo?

java object copy clone
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2 Answers

114

Just follow as below:

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();
    }
}

and wherever you want to get another object, simple perform cloning. e.g: 

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
answered 2010-05-17T09:27:25.760
3

You can deep copy automatically with XStream, from http://x-stream.github.io/:

XStream is a simple library to serialize objects to XML and back again.

Add it to your project (if using 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));

With this you have a copy without the need to implement any cloning interface.

answered 2011-07-25T16:59:42.950

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