how to deep copy object in java?

Question

Possible Duplicate:
How do I copy an object in Java?

Is it ok to do like this in java?

public class CacheTree {

    private Multimap<Integer, Integer> a;
    private Integer                    b;

        public void copy(CacheTree anotherObj) {
            this.a = anotherObj.getA();
            this.b = anotherObj.getB();
        }

       public Multimap<Integer, Integer> getA() {
            return a;
       }

       public Integer getB() {
            return b;
       }
}

public void main() {
     CacheTree x = new CacheTree();
     CacheTree y = new CacheTree();

     x.copy(y);      // Is it ok ?
}

http://stackoverflow.com/questions/64036/how-do-you-make-a-deep-copy-of-an-object-in-java — Hubbitus, May 03 '12 at 17:35

score 4 · Answer 1 · answered Mar 29 '11 at 23:10

4

That's not a deep copy—both objects still refer to the same map.

You need to explicitly create a new MultiMap instance and copy over the contents from the original instance.

answered Mar 29 '11 at 23:10

SLaks

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Erik · Answer 2 · 2011-03-30T06:51:25.570

2

x.a will refer to the same Multimap as y.a - if you add/remove elements to one it'll be reflected in both.

this.a = new Multimap<Integer, Integer>();
this.a.addAll(anotherObj.getA())

That's a deep copy.

edited Mar 30 '11 at 06:51

answered Mar 29 '11 at 23:11

Erik

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How about the Integer x.b? Does it refer to same y.b or not ? – Mar 29 '11 at 23:16
1

Yes, but `Integer`s are immutable, so it doesn't matter. – SLaks Mar 29 '11 at 23:19
So you mean if i make changes in x.b, this will not change y.b ? – Mar 29 '11 at 23:21
@tsubasa: You can't make changes in `x.b`, you can only change `x.b` to another Integer object (and this will not affect the Integer object in `y.b`). – Paŭlo Ebermann Mar 30 '11 at 00:03
I think the second line should be `this.a.addAll(anotherObj.getA())` instead of `getB()`. – Paŭlo Ebermann Mar 30 '11 at 00:04
Note that this wouldn't work if object types in Multimap were mutable. E.g. Foo objects in Multimap or Multimap would need to be deep copied. – Lindlof Jan 23 '15 at 13:10

score 1 · Answer 3 · answered Mar 29 '11 at 23:51

1

See this article, gives a very good example with code in Page 2. It also explains the concept of deep copying in java

http://www.javaworld.com/javaworld/javatips/jw-javatip76.html

answered Mar 29 '11 at 23:51

kensen john

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Thanks for the link! Very useful article indeed. – informatik01 Apr 30 '13 at 20:50

how to deep copy object in java?

3 Answers3