Java ArrayList.retainAll() Method

public boolean retainAll(Collection<?> c)

The retainAll() method is used to remove it's elements from a list that are not contained in the specified collection.

Package: java.util

Java Platform: Java SE 8

Syntax:

retainAll(Collection<?> c)

Parameters:

Return Value:
true if this list changed as a result of the call

Throws:

• ClassCastException - if the class of an element of this list is incompatible with the specified collection (optional)
• NullPointerException - if this list contains a null element and the specified collection does not permit null elements (optional), or if the specified collection is null

Pictorial presentation of ArrayList.retainAll() Method

Example: Java ArrayList.retainAll() Method

The following example the retainAll() method is used to remove it's elements from a list that are not contained in the specified collection.

import java.util.*;

public class test {
   public static void main(String[] args) {
      
    // create an empty array list 
    ArrayList<String> color_list = new ArrayList<String>();

    // use add() method to add values in the list
    color_list.add("White");
    color_list.add("Black");
	color_list.add("Red");
   
   // create an empty array sample with an initial capacity 
	ArrayList<String> sample = new ArrayList<String>();
	
   // use add() method to add values in the list 
    sample.add("Green"); 
	sample.add("Red"); 
	sample.add("White");
		
    System.out.println("First List :"+ color_list);
	System.out.println("Second List :"+ sample);
	
	sample.retainAll(color_list);
	
	System.out.println("After applying the method, First List :"+ color_list);
	System.out.println("After applying the method, Second List :"+ sample);
	
  }
} 
  

Output:

F:\java>javac test.java

F:\java>java test
First List :[White, Black, Red]
Second List :[Green, Red, White]
After applying the method, First List :[White, Black, Red]
After applying the method, Second List :[Red, White]

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