Java Language Cloning performing a deep copy


Example

To copy nested objects, a deep copy must be performed, as shown in this example.

import java.util.ArrayList;
import java.util.List;

public class Sheep implements Cloneable {

    private String name;

    private int weight;

    private List<Sheep> children;

    public Sheep(String name, int weight) {
        this.name = name;
        this.weight = weight;
    }

    @Override
    public Object clone() throws CloneNotSupportedException {
        Sheep clone = (Sheep) super.clone();
        if (children != null) {
            // make a deep copy of the children
            List<Sheep> cloneChildren = new ArrayList<>(children.size());
            for (Sheep child : children) {
                cloneChildren.add((Sheep) child.clone());
            }
            clone.setChildren(cloneChildren);
        }
        return clone;
    }

    public List<Sheep> getChildren() {
        return children;
    }

    public void setChildren(List<Sheep> children) {
        this.children = children;
    }

}

import java.util.Arrays;
import java.util.List;

// create a sheep
Sheep sheep = new Sheep("Dolly", 20);

// create children
Sheep child1 = new Sheep("Child1", 4);
Sheep child2 = new Sheep("Child2", 5);

sheep.setChildren(Arrays.asList(child1, child2));

// clone the sheep
Sheep dolly =  (Sheep) sheep.clone();
List<Sheep> sheepChildren = sheep.getChildren();
List<Sheep> dollysChildren = dolly.getChildren();
for (int i = 0; i < sheepChildren.size(); i++) {
    // prints false, both arrays contain copies of the objects inside
    System.out.println(sheepChildren.get(i) == dollysChildren.get(i));
}