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How to clone an object?

To enable our object to be cloned we need to override Object class clone method. We can also add a java.lang.Cloneable interface to our class, this interface is an empty interface. When we call the clone() method we need the add a try-catch block to catch the CloneNotSupportedException. This exception will be thrown if we tried to clone an object that doesn't suppose to be cloned.

Calling the clone() method does a stateful, shallow copy down inside the Java Virtual Machine (JVM). It creates a new object and copies all the fields from the old object into the newly created object.

package com.javacoderanch.example.lang;

public class CloneDemo implements Cloneable {
    private int number;
    private transient int data;

    /**
     *
     * @return
     * @throws CloneNotSupportedException
     */
    @Override
    protected Object clone() throws CloneNotSupportedException {
        return super.clone();
    }

    public static void main(String[] args) {
        CloneDemo clone = new CloneDemo();
        clone.number = 5;
        clone.data = 1000;

        try {
            //
            // Create a clone of CloneDemo object. When we change the value of
            // number and data field in the cloned object it won't affect the
            // original object.
            //
            CloneDemo objectClone = (CloneDemo) clone.clone();
            objectClone.number = 10;
            objectClone.data = 5000;

            System.out.println("cloned object = " + objectClone);
            System.out.println("origin object = " + clone);
        } catch (CloneNotSupportedException e) {
            e.printStackTrace();
        }
    }

    public String toString() {
        return "[number = " + number + "; data = " + data + "]";
    }
}