Java Data StructuresLesson 65Free preview

Java Set

This lesson is part of Java · All levels

Summary

The set is a collection interface that only stores unique elements, without duplicates at all. The set has no index because the sequence is not guaranteed, so access is done via an iterator or for-each command. The uniqueness of an element is determined by the methods equals() and hashCode().

Key points

Add() returns false when the same element is already in it
No get(i); search using for-each or Iterator
Key implementations: HashSet (fastest), TreeSet (following), LinkedHashSet (following)
Comparison of elements uses equals() and hashCode(), not object references
Some implementations allow exactly one element.

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