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.

Using HashSets

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

// one line HashSet initialise
private static final HashSet<String> exceptions =
      new HashSet<String>(Arrays.asList("platypus", "kangaroo", "wallaby"));

Comparing HashSets for Duplicates

Learning More