The retainAll() method of java.util.TreeSet 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.
TreeSet before retainAll() operation : [1, 2, 3, 4, 5] Collection Elements to be retained : [1, 2, 3] TreeSet after retainAll() operation : [1, 2, 3]
Example 2: For NullPointerException
TreeSet 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
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