How to Deep Copy Arraylist in Java

In this article, we are going to learn deep copy ArrayList in Java.

There are mainly two concepts Shallow copy and deep copy.

When an object gets copied via reference not actual values then it is called Shallow copy. In it, changes made to an object will also reflect to another object. It means if we change elements of one object then the other object will also be changed.

In deep copy, the copied object is completely independent and changes made to it do not reflect to the original object.
Let’s understand with the examples.

Example of Deep Copy ArrayList

Here, we are copying one ArrayList elements to ther using addAll() method and see changes made to second list does not modify original list.

Output:

[India, US, China] [India, US, China] [India, Russia, China]

Note: This method will only work if ArrayList contains primitive data types or immutable collection. In case, ArrayList contains custom objects, then we need to explicitly clone the custom objects.

Deep Copy using Clone() Method

We can also use clone() method to create a copy of ArrayList but this method create swallow copy.

Let’s see with the help of example.

Create main class named CloneArrayListMain.java

Output

———–Original List———–
John 102
David 105
———–Copied List———-
John 102
David 105

As you can see, changes to clonedStudentList also got reflected in studentList.

To create a true deep copy of ArrayList, we should create a new ArrayList and copy all the cloned elements to new ArrayList one by one and we should also clone Student object properly.

To create deep copy of Student class, we can divide its class members to mutable and immutable types.

  • Immutable fields( String data types): We can directly use immutable fields in cloned object. Immutable fields include wrapper classes, String and primitive types.
  • Mutable fields(Date data type): We should create new object for the mutable attribute and then assign it to cloned object.

Here is the correct clone method for Student class.

As you can see, we have used super.clone() to clone the Student object and then set dateOfBirth explicitly to clonedStudent as Date is mutable field.

Here is code to create deep copy of ArrayList by copying cloned elements one by one to new ArrayList.

Complete code to deep copy ArrayList in java

Here is complete java program to create deep copy of ArrayList in java.

As you can see, changes made to clonedStudentList did not reflect in original ArrayList studentList.

That’s all about how to deep copy ArrayList in java.


import_contacts

You may also like:

Related Posts

  • 10 September

    How to remove element from Arraylist in java while iterating

    Table of ContentsIntroductionUsing Collection’s removeIf() methodUsing ListIterator classUsing removeAll() methodUsing Java 8 Stream to filter List itemsConclusion Introduction In this tutorial, you will learn how to remove element from Arraylist in java while iterating using different implementations provided by Java. It is necessary to understand the right way to remove items from a List because […]

  • Print HashMap in java
    30 June

    Print HashMap in Java

    Table of ContentsPrint from the HashMap ReferencePrint HashMap using foreach method with keyset()Print HashMap using Consumer with entrySet()Print HashMap using Arrays’s asList() methodPrint HashMap using Collections’s singletonList()Print HashMap using getkey() and getValue with entrySet()Print HashMap using BiConsumerPrint HashMap using IteratorPrint HashMap using custom ObjectsConclusion In this article, we will see how to print HashMap in […]

  • Print LinkedList in java
    26 June

    Print LinkedList in java

    Table of ContentsJava inbuilt LinkedListPrint LinkedList using a for loopPrint LinkedList using Enhanced for loopPrint LinkedList using streamsPrint LinkedList using toString() methodPrint LinkedList using IteratorPrint LinkedList using custom objectsCustom singly LinkedListHow to print a custom singly LinkedListConclusion Java inbuilt LinkedList Java inbuilt LinkedList class uses doubly linked list as internal data structure to store its […]

  • Java Set to Array
    12 May

    Java Set to Array

    Table of Contents1. Using Java 8’s Stream2. Using toArray()3. Using toArray(IntFunction) [Java 11]4. Using System.arraycopy()5. Using Arrays.copyOf6. Using simple iteration7. Using Guava library7.1 Using FluentIterable7.2 Using Iterables In this post, we will learn java set to array conversion. There are many ways to convert set to an array. 1. Using Java 8’s Stream If you […]

  • Print ArrayList in java
    11 May

    Print ArrayList in Java

    Learn about how to print ArrayList in java in different ways.

  • 02 October

    Initialize ArrayList with values in Java

    Table of ContentsUsing Arrays.asList()Initialize ArrayList with String valuesintialize ArrayList with Integer valuesintialize ArrayList with float valuesUsing Stream in Java 8Using Factory Method in java 9Using double braces In this article, we will learn to initialize ArrayList with values in Java. ArrayList is an implementation class of List interface in Java. It is used to store […]

Leave a Reply

Your email address will not be published. Required fields are marked *

Subscribe to our newletter

Get quality tutorials to your inbox. Subscribe now.