Wednesday, September 22, 2010

Set<E> interface

Sets are collections that allow only one object with a given value in them. The java.util.Set interface is a subinterface of Collection. There are two very useful concrete classes that implement the Set interface:
  • java.util.HashSet is implemented with a hash table. Access time is O(1). Entries are unsorted.
  • java.util.TreeSet is implemented as a balanced binary tree. Access time is O(log N). Entries are sorted.

A set is an unordered collection of elements that has no duplicate members. elements retrieved by identity, not index.

Set Interface

Set Implementations

We have following as implementing classes:

public interface Set {
// Basic Operations
int size();
boolean isEmpty();
boolean contains(Object element);
boolean add(Object element); // Optional
boolean remove(Object element); // Optional
Iterator iterator();

// Bulk Operations
boolean containsAll(Collection c);
boolean addAll(Collection c); // Optional
boolean removeAll(Collection c); // Optional
boolean retainAll(Collection c); // Optional
void clear(); // Optional

// Array Operations
Object[] toArray();
Object[] toArray(Object a[]);

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