The retainAll() method of java.util.LinkedHashSet class is used to retain from this set all of its elements that are contained in the specified collection.
public boolean retainAll(Collection c)
Parameters: This method takes collection c as a parameter containing elements to be retained from this set.
Returns Value: This method returns true if this set 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.
Below are the examples to illustrate the retainAll() method.
LinkedHashSet before retainAll() operation : [1, 2, 3, 4, 5] Collection Elements to be retained : [1, 2, 3] LinkedHashSet after retainAll() operation : [1, 2, 3]
Example 2: For NullPointerException
LinkedHashSet before retainAll() operation : [1, 2, 3, 4, 5] Collection Elements to be retained : null Trying to pass null as a specified element Exception thrown : java.lang.NullPointerException
Attention reader! Don’t stop learning now. Get hold of all the important Java Foundation and Collections concepts with the Fundamentals of Java and Java Collections Course at a student-friendly price and become industry ready. To complete your preparation from learning a language to DS Algo and many more, please refer Complete Interview Preparation Course.