In this tutorial, you will learn how to use the HashSet class with coding examples.

Following are few key points to note about HashSet in Java -

• HashSet cannot contain duplicate values.
• HashSet allows null value.
• HashSet is an unordered collection. It does not maintain the order in which the elements are inserted.
• HashSet internally uses a HashMap to store its elements.
• HashSet is not thread-safe. If multiple threads try to modify a HashSet at the same time, then the final outcome is not deterministic. You must explicitly synchronize concurrent access to a HashSet in a multi-threaded environment.

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