Question

I’d like to copy a vector to another. The problem is that if I change the vector v1, the second vector v2 is changing too. My goal is to keep the copy intact even if I change the source vector.

import java.util.Collections;
import java.util.Vector;

public class CopyElementsOfVectorToVectorExample {

  public static void main(String[] args) {

    //create first Vector object
    Vector v1 = new Vector();

    //Add elements to Vector
    v1.add("1");
    v1.add("2");
    v1.add("3");

    //create another Vector object
    Vector v2 = new Vector(v1.size());  

    v2.setSize(v1.size());
    Collections.copy(v2,v1);


    System.out.println("After copy, Second Vector Contains : " + v2);  
  }}

How can I keep the second copy intact?

Answer 1

the problem is if I change the vector v1, the second v2 is changing too ...My goal is to keep the copy intact even if I change the source vector

This is because Collections.copy(v2,v1) make a sallow copy not deep copy.

Make deep copy of your Vector.

Apologize for previous answer.

Edit:

I am assuming that your vector is containing objects of type Serializable. With this approach you can get a deep copy of your collection.

static public Object deepCopy(Object oldObj) throws Exception {
    ObjectOutputStream oos = null;
    ObjectInputStream ois = null;
    try {
        ByteArrayOutputStream bos = new ByteArrayOutputStream(); // A
        oos = new ObjectOutputStream(bos); // B
        // serialize and pass the object
        oos.writeObject(oldObj); // C
        oos.flush(); // D
        ByteArrayInputStream bin = new ByteArrayInputStream(
                bos.toByteArray()); // E
        ois = new ObjectInputStream(bin); // F
        // return the new object
        return ois.readObject(); // G
    } catch (Exception e) {
        System.out.println("Exception in ObjectCloner = " + e);
        throw (e);
    } finally {
        oos.close();
        ois.close();
    }
}