Set JDK 1.6)

Description

public interface Set

A collection that contains no duplicate elements.

A collection that contains no duplicate elements. More formally, sets contain no pair of elements e1 and e2 such that e1.equals(e2), and at most one null element. As implied by its name, this interface models the mathematical set abstraction.

The Set interface places additional stipulations, beyond those inherited from the Collection interface, on the contracts of all constructors and on the contracts of the add, equals and hashCode methods. Declarations for other inherited methods are also included here for convenience. (The specifications accompanying these declarations have been tailored to the Set interface, but they do not contain any additional stipulations.)

The additional stipulation on constructors is, not surprisingly, that all constructors must create a set that contains no duplicate elements (as defined above).

Note: Great care must be exercised if mutable objects are used as set elements. The behavior of a set is not specified if the value of an object is changed in a manner that affects equals comparisons while the object is an element in the set. A special case of this prohibition is that it is not permissible for a set to contain itself as an element.

Some set implementations have restrictions on the elements that they may contain. For example, some implementations prohibit null elements, and some have restrictions on the types of their elements. Attempting to add an ineligible element throws an unchecked exception, typically NullPointerException or ClassCastException. Attempting to query the presence of an ineligible element may throw an exception, or it may simply return false; some implementations will exhibit the former behavior and some will exhibit the latter. More generally, attempting an operation on an ineligible element whose completion would not result in the insertion of an ineligible element into the set may throw an exception or it may succeed, at the option of the implementation. Such exceptions are marked as "optional" in the specification for this interface.

This interface is a member of the Java Collections Framework.

See also: Collection List SortedSet HashSet TreeSet AbstractSet Collections.singleton(java.lang.Object) Collections.EMPTY_SET

Methods

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public boolean add ( E e) [Specified in Collection]

Adds the specified element to this set if it is not already present (optional operation).

public boolean addAll (Collection<Object> c) [Specified in Collection]

Adds all of the elements in the specified collection to this set if they're not already present (optional operation).

public void clear () [Specified in Collection]

Removes all of the elements from this set (optional operation).

public boolean contains (Object o) [Specified in Collection]

Returns true if this set contains the specified element.

public boolean containsAll (Collection<Object> c) [Specified in Collection]

Returns true if this set contains all of the elements of the specified collection.

public boolean equals (Object o) [Specified in Collection]

Compares the specified object with this set for equality.

public int hashCode () [Specified in Collection]

Returns the hash code value for this set.

public boolean isEmpty () [Specified in Collection]

Returns true if this set contains no elements.

public Iterator< E> iterator () [Specified in Collection]

Returns an iterator over the elements in this set.

public boolean remove (Object o) [Specified in Collection]

Removes the specified element from this set if it is present (optional operation).

public boolean removeAll (Collection<Object> c) [Specified in Collection]

Removes from this set all of its elements that are contained in the specified collection (optional operation).

public boolean retainAll (Collection<Object> c) [Specified in Collection]

Retains only the elements in this set that are contained in the specified collection (optional operation).

public int size () [Specified in Collection]

Returns the number of elements in this set (its cardinality).

public Object toArray () [Specified in Collection]

Returns an array containing all of the elements in this set.

public T toArray ( T a) [Specified in Collection]

Returns an array containing all of the elements in this set; the runtime type of the returned array is that of the specified array.

Returns an array containing all of the elements in this set; the runtime type of the returned array is that of the specified array. If the set fits in the specified array, it is returned therein. Otherwise, a new array is allocated with the runtime type of the specified array and the size of this set.

If this set fits in the specified array with room to spare (i.e., the array has more elements than this set), the element in the array immediately following the end of the set is set to null. (This is useful in determining the length of this set only if the caller knows that this set does not contain any null elements.)

If this set makes any guarantees as to what order its elements are returned by its iterator, this method must return the elements in the same order.

Like the Set.toArray() method, this method acts as bridge between array-based and collection-based APIs. Further, this method allows precise control over the runtime type of the output array, and may, under certain circumstances, be used to save allocation costs.

Suppose x is a set known to contain only strings. The following code can be used to dump the set into a newly allocated array of String:

     String[] y = x.toArray(new String[0]);

Note that toArray(new Object[0]) is identical in function to toArray().
Returns: an array containing all the elements in this set
Parameters:
- a - the array into which the elements of this set are to be stored, if it is big enough; otherwise, a new array of the same runtime type is allocated for this purpose.
Throws:
- ArrayStoreException - if the runtime type of the specified array is not a supertype of the runtime type of every element in this set
- NullPointerException - if the specified array is null