HashSet : Java Glossary

You’d think HashSet would be a useful tool for arranging unique Objects. However, it is useless for that purpose because it will only tell you if an equivalent Object is already in the HashSet. It won’t divulge a reference to the canonical Object itself. To arrange uniqueness, you need a HashMap with key and value referencing the same canonical unique Object.

In other words, HashSet.contains tells you if there is an Object in the HashSet Collection that matches yours, as measured by equals. It does not tell you if your Object is the exact same Object as the one in the Collection. Further, HashSet will not give you a reference to its Object. However, if you use HashMap instead, you can get a reference to the Collection’s Object.

Using HashSets

Here is how you can initialise a HashSet in a single line.

Comparing HashSets for Duplicates

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