ArrayList addAll() method in Java

In this article, we will see how to add other collection elements in the ArrayList. Also, we will see how to add other collection elements from any particular index in ArrayList.

Introduction

ArrayList is a widely used class from the Collection framework in Java. ArrayList used a dynamic array internally to store the elements.

When we add objects to ArrayList, it maintains the insertion order. So, ArrayList is an ordered collection.

Also, duplicate objects are allowed in ArrayList.

Sometimes we need to add the elements of another collection to the ArrayList. The arrayList call provides the addAll() method to add the elements of the collection.

The addAll() method has two overload type

1. addAll(Collection c)
2. addAll(int index, Collection c)

The first ArrayList method adds the elements of the specified collection to the end of the ArrayList.

The second ArrayList method adds the elements of the specified collection at the specified index.

Let’s see both the methods one by one.

1. Add a collection in ArrayList using the addAll(Collection c) method

The addAll(Collection c) method adds all the elements of the specified collection to the end of the ArrayList.

The method signature for this method is given below.

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public boolean addAll(Collection c)

The method signature shows that this method accepts one parameter of type Collection.

• c : - any collection obejct

It has a return type as boolean i.e. this method returns true if the ArrayList as a result of the call (if elements from other collections are added to the ArrayList), otherwise it returns false.

This method may throw NullPointerException if the specified collection is empty

I have given a java program to add elements of a collection to ArrayList using the addAll(Collection c) method.

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

/**
 * A Java program to add all elements of the specified collection
 * to the end of the ArrayList
 * 
 * @author Gaurav Kukade at coderolls.com
 *
 */
public class ArrayListAddAllExample {

  public static void main(String[] args) {
    // ArrayList contains actresses
    List<String> actresses1 = new ArrayList<String>();
    
    actresses1.add("Natalie Portman");
    actresses1.add("Abigail Anderson");
    actresses1.add("Jennifer Lawrence");
    
    System.out.println("Actresses collection 1: \n"+ actresses1 );
    
    // ArrayList contains actresses
    List<String> actresses2 = new ArrayList<String>();  
    
    actresses2.add("Angelina Jolie");
    actresses2.add("Scarlett Johansson");
    
    System.out.println("Actresses collection 2: \n"+ actresses2);
    
    // Add actresses2 collections all elements to actresses1 collection using addAll()method
    actresses1.addAll(actresses2);
    
    System.out.println("Actresses : \n"+ actresses1);
  }
}

Output:

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Actresses collection 1: 
[Natalie Portman, Abigail Anderson, Jennifer Lawrence]
Actresses collection 2: 
[Angelina Jolie, Scarlett Johansson]
Actresses : 
[Natalie Portman, Abigail Anderson, Jennifer Lawrence, Angelina Jolie, Scarlett Johansson]

2. Add a collection in ArrayList at a particular index using the addAll(int index, Collection c) method

The addAll(int index, Collection c) method adds all the elements of the specified collection to the ArrayList from the specified index.

The method signature for this method is as given below.

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public boolean addAll(int index, Collection c)

This method accepts two parameters,

• c: - a collection c whose elements need to be added to the ArrayList
• index: - an index of type int, it specifies the position in ArrayList from collection c’s elements will be added.

It returns true if the ArrayList got changed, otherwise false

This method may throw the following exceptions

• IndexOutOfBoundsException - if the index is out of range (index < 0

  index > arraList.size())

• NullPointerException, if the specified collection is empty

I have given a Java program to add elements of a collection to ArrayList at a particular index using the addAll(Collection c) method.

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

/**
 * A Java program to add all elements of the specified collection
 * to the ArrayList from a particular index 
 * 
 * @author coderolls.com
 *
 */
public class ArrayListAddAllExample2 {

  public static void main(String[] args) {
    // ArrayList containing entrepreneurs
    List<String> entrepreneurs1 = new ArrayList<String>();
    
    entrepreneurs1.add("Bill Gates");
    entrepreneurs1.add("Steve Jobs");
    entrepreneurs1.add("Jeff Bezos");
    entrepreneurs1.add("Richard Branson");
    entrepreneurs1.add("Mark Cuban");
    
    System.out.println("Entrepreneurs Collection 1: \n"+ entrepreneurs1 );
    
    // ArrayList containing entrepreneurs
    List<String> entrepreneurs2 = new ArrayList<String>();
    
    entrepreneurs2.add("Mark Zuckerberg");
    entrepreneurs2.add("Larry Page");
    entrepreneurs2.add("Larry Ellison");
    
    System.out.println("Entrepreneurs collection 2: \n"+ entrepreneurs2);
    
    // Add entrepreneurs2 collections all elements to entrepreneurs1 Collection
    // starting from index 2
    entrepreneurs1.addAll(2, entrepreneurs2);
    
    System.out.println("Entrepreneurs : \n"+ entrepreneurs1);
  }
}

Output:

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Entrepreneurs Collection 1: 
[Bill Gates, Steve Jobs, Jeff Bezos, Richard Branson, Mark Cuban]
Entrepreneurs Collection 2: 
[Mark Zuckerberg, Larry Page, Larry Ellison]
Entrepreneurs : 
[Bill Gates, Steve Jobs, Mark Zuckerberg, Larry Page, Larry Ellison, Jeff Bezos, Richard Branson, Mark Cuban]

Conclusion

We can add elements of a collection to the ArrayList using the addAll() method in two ways.

1. addAll(Collection c) - it adds elements of the specified collection to the end of ArrayList
2. addAll(int index, Collection c) - it adds elements of the specified collection to the ArrayList from the specified position (index)

The example Java programs given in the above tutorial can be found at this GitHub Repository.

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