Set retainAll() method in Java with Example
The retainAll() method of java.util.Set interface is used to retain from this set all of its elements that are contained in the specified collection.
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public boolean retainAll(Collection c)
Parameters: This method takes collection c as a parameter containing elements to be retained from this set.
Return 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.
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.
Set 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