Last Updated : 12 Jul, 2025
The retainAll() method of SortedSet interface is used to retain from this SortedSet, all of its elements that are contained in the specified collection.
Syntax:
public boolean retainAll(Collection c)
Parameters: This method takes collection c as a parameter containing elements to be retained from this SortedSet.
Return Value: This method returns true if this SortedSet changed as a result of the call.
Exception: This method throws NullPointerException if this set contains a null element and the specified collection does not permit null elements (optional), or if the specified collection is null.
Note: The retainAll() method in SortedSet is inherited from the Set interface in Java.
Below are the examples to illustrate the retainAll() method.
Example 1:
Java
// Java program to demonstrate
// retainAll() method for Sorted set
import java.util.*;
public class GFG1 {
public static void main(String[] args)
throws Exception
{
try {
// Creating object of Set
SortedSet<Integer> arrset1
= new TreeSet<Integer>();
// Populating arrset1
arrset1.add(1);
arrset1.add(2);
arrset1.add(3);
arrset1.add(4);
arrset1.add(5);
// print arrset1
System.out.println(
"Set before "
+ "retainAll() operation : "
+ arrset1);
// Creating another object of Set
SortedSet<Integer> arrset2
= new TreeSet<Integer>();
arrset2.add(1);
arrset2.add(2);
arrset2.add(3);
// print arrset2
System.out.println(
"Collection Elements"
+ " to be retained : "
+ arrset2);
// Removing elements from arrset
// specified in arrset2
// using retainAll() method
arrset1.retainAll(arrset2);
// print arrset1
System.out.println(
"Set after "
+ "retainAll() operation : "
+ arrset1);
}
catch (NullPointerException e) {
System.out.println(e);
}
}
}
Set before retainAll() operation : [1, 2, 3, 4, 5] Collection Elements to be retained : [1, 2, 3] Set after retainAll() operation : [1, 2, 3]
Example 2: For NullPointerException.
Java
// Java program to demonstrate
// retainAll() method for Sorted set
import java.util.*;
public class GFG1 {
public static void main(String[] args)
throws Exception
{
try {
// Creating object of SortedSet<Integer>
SortedSet<Integer> arrset1
= new TreeSet<Integer>();
// Populating arrset1
arrset1.add(1);
arrset1.add(2);
arrset1.add(3);
arrset1.add(4);
arrset1.add(5);
// print arrset1
System.out.println(
"Set before "
+ "retainAll() operation : "
+ arrset1);
// Creating another object of Set<Integer>
SortedSet<Integer> arrset2 = null;
// print arrset2
System.out.println(
"Collection Elements "
+ "to be retained : "
+ arrset2);
System.out.println(
"\nTrying to pass "
+ "null as a "
+ "specified element\n");
// Removing elements from arrset
// specified in arrset2
// using retainAll() method
arrset1.retainAll(arrset2);
// print arrset1
System.out.println(
"Set after "
+ "retainAll() operation : "
+ arrset1);
}
catch (NullPointerException e) {
System.out.println(e);
}
}
}
Set before retainAll() operation : [1, 2, 3, 4, 5] Collection Elements to be retained : null Trying to pass null as a specified element java.lang.NullPointerException
Reference: https://docs.oracle.com/javase/7/docs/api/java/util/Set.html#retainAll(java.util.Collection)
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