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SortedSet TreeSet

layout: default title: SortedSet Interface and TreeSet Cla

SortedSet is a subinterface of Set, which guarantees that its elements will be ordered.

SortedSet family

SortedSet Methods

SortedSet adds two important methods, since it is ordered.

  • E first() - returns the first (lowest) element currently in this set.
  • E last() - returns the last (highest) element currently in this set.

TreeSet Implementation Class

TreeSet orders elements according to their natural ordering.

natural ordering

An ordering built into a class (in a method) so that instance A can compare itself to instance B to determine if it is less than, equal to, or greater than instance B.

For example, the natural ordering of Integer is smallest to largest, because every Integer object can look at another Integer object and determine whose number is larger.


Practice Exercise

TreeSet must maintain ordering as objects are added, so it has to compare the new object to current objects to determine where the new one goes.

These comparison operations cost time, so make sure you have a reason to order elements before choosing to use TreeSet.

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