ArrayList clone() – ArrayList deep copy and shallow copy

Example program to ArrayList clone method example. ArrayList deep copy and shallow copy examples on Student Objects.

1. Introduction

ArrayList clone() – ArrayList deep copy and shallow copy. ArrayList clone() method is used to create a shallow copy of the list. In the new list, only object references are copied. If we change the object state inside the first ArrayList, then the changed object state will be reflected in the cloned ArrayList as well.

2. ArrayList Clone – Shallow Copy Example

Example program to copy List of String to anther list with clone().

package com.java.oraclejavacertified.blog.arraylist;

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

/**
 *
 * Java ArrayList Clone Example
 *
 *
 */
public class ArrayListCloneExample {

 public static void main(String[] args) {

  ArrayList<String> list = new ArrayList<>();
  list.add("one");
  list.add("two");
  list.add("three");
  list.add("four");
  list.add("give");

  System.out.println("Before clone : " + list);

  ArrayList clonedLis = (ArrayList) list.clone();
 
  System.out.println("After clone : "+clonedLis);

 }

}

Output:

Before clone : [one, two, three, four, give]
After clone : [one, two, three, four, give]

3. ArrayList clone – Custom Shallow Copy Example

Example program to ArrayList shallow copy with custom objects. Modifications to the cloned objects are reflected in the original objects. Observer the output of this program.

package com.java.oraclejavacertified.blog.arraylist;

import java.util.ArrayList;

/**
 *
 * Java ArrayList Clone Example with custom object
 *
 *
 */
public class ArrayListShalloCloneExample {

 public static void main(String[] args) {

  ArrayList<Student> list = new ArrayList<>();
  list.add(new Student(100, "harish"));
  list.add(new Student(101, "Jayaram"));

  ArrayList<Student> clonedList = (ArrayList) list.clone();

  Student student = clonedList.get(1);
  student.setName("Jhon");

  System.out.println("Cloned list : " + clonedList);
  System.out.println("Original list : " + list);

 }

}

class Student {

 private int id;
 private String name;

 public Student(int id, String name) {
  super();
  this.id = id;
  this.name = name;
 }

 public int getId() {
  return id;
 }

 public void setId(int id) {
  this.id = id;
 }

 public String getName() {
  return name;
 }

 public void setName(String name) {
  this.name = name;
 }

 @Override
 public String toString() {
  return "Student [id=" + id + ", name=" + name + "]";
 }

}

Output:

Cloned list : [Student [id=100, name=harish], Student [id=101, name=Jhon]]

Original list : [Student [id=100, name=harish], Student [id=101, name=Jhon]]

4. ArrayList Clone – Deep Copy Example

The below program creates a deep copy of objects. Modifications to the cloned list will not affect the original list.

public class ArrayListDeepCloneExample {

 public static void main(String[] args) {

  ArrayList<Student> list = new ArrayList<>();

  list.add(new Student(100, "harish"));

  list.add(new Student(101, "Jayaram"));

  ArrayList<Student> clonedList = new ArrayList<>();

  Iterator<Student> it = list.iterator();

  while (it.hasNext()) {

   Student s = it.next();

   Student newS = new Student(s.getId(), s.getName());

   clonedList.add(newS);

  }

  Student student = clonedList.get(1);

  student.setName("Jhon");

  System.out.println("Cloned list : " + clonedList);

  System.out.println("Original list : " + list);

 }

}

Output:

Cloned list : [Student [id=100, name=harish], Student [id=101, name=Jhon]]

Original list : [Student [id=100, name=harish], Student [id=101, name=Jayaram]]