Java ArrayList retainAll() Function

July 20, 2023

What is an ArrayList?

Arraylist is a part of collection framework in java. It contains some inbuilt function like retainAll() function which can be found in the java.util.ArrayList Package.
It implements the List interface of the collections framework.

Here, in the page we will discuss about the ArrayList’s retainAll() Method in java. To know more about ArrayList in java, you can click on the button given below.

ArrayList retainAll Function:

Arraylist contains several inbuilt functions that are used to perform several operations on arraylist in Java. The retainAll function is also an inbuilt method of class ArrayList.
The retainAll function removes all those elements of an ArrayList that are not present in the specified class of collection. It retains only those elements in the ArrayList that are similar to the specified class of collection.

Syntax:

arraylist_name.retainAll(Contain c)

Definition of Parameters:

arrayList_name : This is the final list obtained after retaining the required elements.

Collection c : This is the collection class with which the ArrayList is Compared.

Return Type :

True : If the operation is performed successfully.

UnsupportedOperationException : if the retainAll operation is not supported by this set.

NullPointerException : if ArrayList contains a null element and the specified collection does not permit null elements.

Remove() Function

Removeall() Function

Removeif() Function

Removerange() Function

Replaceall() Function

Example for Retaining Elements of ArrayList of Integers:

Run

import java.util.*;

public class Main{
    public static void main(String[] args){
        ArrayList<Integer> Prep = new ArrayList<>();
        Prep.add(1);
        Prep.add(2);
        Prep.add(3);
        Prep.add(4);
        
        ArrayList<Integer> Insta = new ArrayList<>();
        Insta.add(5);
        Insta.add(2);
        Insta.add(6);
        Insta.add(3);
        
        System.out.println("ArrayList Prep : " + Prep);
        System.out.println("ArrayList Insta : " + Insta);
        Prep.retainAll(Insta);
        System.out.println("After Performing Operation on Prep : " + Prep);
    }
}

Output:

ArrayList Prep : [1, 2, 3, 4]
ArrayList Insta : [5, 2, 6, 3]
After Performing Operation on Prep : [2, 3]

In the above Example, We had taken two ArrayList “Prep” and “Insta” of integer type, we are passing the ArrayList “Insta” as an argument to the retainAll Function.

Example for Retaining Elements of ArrayList of Strings:

Run

import java.util.*;

public class Main{
    public static void main(String[] args){
        ArrayList<String> Prep = new ArrayList<>();
        Prep.add("C");
        Prep.add("C++");
        Prep.add("Java");
        Prep.add("Python");
        
        ArrayList<String> Insta = new ArrayList<>();
        Insta.add("Java");
        Insta.add("Python");
        Insta.add("Java Script");
        
        System.out.println("ArrayList Prep : " + Prep);
        System.out.println("ArrayList Insta : " + Insta);
        Prep.retainAll(Insta);
        System.out.println("After Performing Operation on Prep : " + Prep);
    }
}

Output:

ArrayList Prep : [C, C++, Java, Python]
ArrayList Insta : [Java, Python, Java Script]
After Performing Operation on Prep : [Java, Python]

In the above Example. we have created two ArrayLists “Prep” and “Insta” of String Type, we are passing the ArrayList “Insta” as an argument to the retainAll Function.

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