java.util
Class Collections.UnmodifiableSet

java.lang.Object
  java.util.Collections.UnmodifiableCollection
      java.util.Collections.UnmodifiableSet

All Implemented Interfaces:

Collection, Serializable, Set

Direct Known Subclasses:

Collections.UnmodifiableMap.UnmodifiableEntrySet, Collections.UnmodifiableSortedSet

Enclosing class:

Collections

static class Collections.UnmodifiableSet

extends Collections.UnmodifiableCollection

implements Set, Serializable

See Also:

Serialized Form

Field Summary

(package private) Collection

c

Constructor Summary

(package private)

Collections.UnmodifiableSet(Set s)

Method Summary

boolean	add(Object o) Adds the specified element to this set if it is not already present (optional operation).
boolean	addAll(Collection coll) Adds all of the elements in the specified collection to this set if they're not already present (optional operation).
void	clear() Removes all of the elements from this set (optional operation).
boolean	contains(Object o) Returns true if this set contains the specified element.
boolean	containsAll(Collection coll) Returns true if this set contains all of the elements of the specified collection.
boolean	equals(Object o) Compares the specified object with this set for equality.
int	hashCode() Returns the hash code value for this set.
boolean	isEmpty() Returns true if this set contains no elements.
Iterator	iterator() Returns an iterator over the elements in this set.
boolean	remove(Object o) Removes the specified element from this set if it is present (optional operation).
boolean	removeAll(Collection coll) Removes from this set all of its elements that are contained in the specified collection (optional operation).
boolean	retainAll(Collection coll) Retains only the elements in this set that are contained in the specified collection (optional operation).
int	size() Returns the number of elements in this set (its cardinality).
Object[]	toArray() Returns an array containing all of the elements in this set.
Object[]	toArray(Object[] a) Returns an array containing all of the elements in this set; the runtime type of the returned array is that of the specified array.
String	toString() Returns a string representation of the object.

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Methods inherited from interface java.util.Set

add, addAll, clear, contains, containsAll, isEmpty, iterator, remove, removeAll, retainAll, size, toArray, toArray

Field Detail

c

Collection c

Constructor Detail

Collections.UnmodifiableSet

Collections.UnmodifiableSet(Set s)

Method Detail

equals

public boolean equals(Object o)

Description copied from interface: Set

Compares the specified object with this set for equality. Returns true if the specified object is also a set, the two sets have the same size, and every member of the specified set is contained in this set (or equivalently, every member of this set is contained in the specified set). This definition ensures that the equals method works properly across different implementations of the set interface.

Specified by:

equals in interface Set

Overrides:

equals in class Object

Parameters:

o - the reference object with which to compare.

Returns:

true if this object is the same as the obj argument; false otherwise.

See Also:

Object.hashCode(), Hashtable

hashCode

public int hashCode()

Description copied from interface: Set

Returns the hash code value for this set. The hash code of a set is defined to be the sum of the hash codes of the elements in the set, where the hashcode of a null element is defined to be zero. This ensures that s1.equals(s2) implies that s1.hashCode()==s2.hashCode() for any two sets s1 and s2, as required by the general contract of the Object.hashCode method.

Specified by:

hashCode in interface Set

Overrides:

hashCode in class Object

Returns:

a hash code value for this object.

See Also:

Object.equals(java.lang.Object), Hashtable

size

public int size()

Description copied from interface: Collection

Returns the number of elements in this collection. If this collection contains more than Integer.MAX_VALUE elements, returns Integer.MAX_VALUE.

Specified by:

size in interface Collection

Returns:

the number of elements in this collection

isEmpty

public boolean isEmpty()

Description copied from interface: Collection

Returns true if this collection contains no elements.

Specified by:

isEmpty in interface Collection

Returns:

true if this collection contains no elements

contains

public boolean contains(Object o)

Description copied from interface: Collection

Returns true if this collection contains the specified element. More formally, returns true if and only if this collection contains at least one element e such that (o==null ? e==null : o.equals(e)).

Specified by:

contains in interface Collection

Parameters:

o - element whose presence in this collection is to be tested.

Returns:

true if this collection contains the specified element

toArray

public Object[] toArray()

Description copied from interface: Collection

Returns an array containing all of the elements in this collection. If the collection makes any guarantees as to what order its elements are returned by its iterator, this method must return the elements in the same order.

The returned array will be "safe" in that no references to it are maintained by this collection. (In other words, this method must allocate a new array even if this collection is backed by an array). The caller is thus free to modify the returned array.

This method acts as bridge between array-based and collection-based APIs.

Specified by:

toArray in interface Collection

Returns:

an array containing all of the elements in this collection

toArray

public Object[] toArray(Object[] a)

Description copied from interface: Collection

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

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

If this collection 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 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 l is a List known to contain only strings. The following code can be used to dump the list into a newly allocated array of String:

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

Note that toArray(new Object[0]) is identical in function to toArray().

Specified by:

toArray in interface Collection

Parameters:

a - the array into which the elements of this collection are to be stored, if it is big enough; otherwise, a new array of the same runtime type is allocated for this purpose.

Returns:

an array containing the elements of this collection

toString

public String toString()

Description copied from class: Object

Returns a string representation of the object. In general, the toString method returns a string that "textually represents" this object. The result should be a concise but informative representation that is easy for a person to read. It is recommended that all subclasses override this method.

The toString method for class Object returns a string consisting of the name of the class of which the object is an instance, the at-sign character `@', and the unsigned hexadecimal representation of the hash code of the object. In other words, this method returns a string equal to the value of:

 getClass().getName() + '@' + Integer.toHexString(hashCode())
 

Overrides:

toString in class Object

Returns:

a string representation of the object.

iterator

public Iterator iterator()

Description copied from interface: Collection

Returns an iterator over the elements in this collection. There are no guarantees concerning the order in which the elements are returned (unless this collection is an instance of some class that provides a guarantee).

Specified by:

iterator in interface Collection

Returns:

an Iterator over the elements in this collection

add

public boolean add(Object o)

Description copied from interface: Collection

Ensures that this collection contains the specified element (optional operation). Returns true if this collection changed as a result of the call. (Returns false if this collection does not permit duplicates and already contains the specified element.)

Collections that support this operation may place limitations on what elements may be added to this collection. In particular, some collections will refuse to add null elements, and others will impose restrictions on the type of elements that may be added. Collection classes should clearly specify in their documentation any restrictions on what elements may be added.

If a collection refuses to add a particular element for any reason other than that it already contains the element, it must throw an exception (rather than returning false). This preserves the invariant that a collection always contains the specified element after this call returns.

Specified by:

add in interface Collection

Parameters:

o - element whose presence in this collection is to be ensured.

Returns:

true if this collection changed as a result of the call

remove

public boolean remove(Object o)

Description copied from interface: Collection

Removes a single instance of the specified element from this collection, if it is present (optional operation). More formally, removes an element e such that (o==null ? e==null : o.equals(e)), if this collection contains one or more such elements. Returns true if this collection contained the specified element (or equivalently, if this collection changed as a result of the call).

Specified by:

remove in interface Collection

Parameters:

o - element to be removed from this collection, if present.

Returns:

true if this collection changed as a result of the call

containsAll

public boolean containsAll(Collection coll)

Description copied from interface: Collection

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

Specified by:

containsAll in interface Collection

Parameters:

coll - collection to be checked for containment in this collection.

Returns:

true if this collection contains all of the elements in the specified collection

See Also:

Collection.contains(Object)

addAll

public boolean addAll(Collection coll)

Description copied from interface: Collection

Adds all of the elements in the specified collection to this collection (optional operation). The behavior of this operation is undefined if the specified collection is modified while the operation is in progress. (This implies that the behavior of this call is undefined if the specified collection is this collection, and this collection is nonempty.)

Specified by:

addAll in interface Collection

Parameters:

coll - elements to be inserted into this collection.

Returns:

true if this collection changed as a result of the call

See Also:

Collection.add(Object)

removeAll

public boolean removeAll(Collection coll)

Description copied from interface: Collection

Removes all this collection's elements that are also contained in the specified collection (optional operation). After this call returns, this collection will contain no elements in common with the specified collection.

Specified by:

removeAll in interface Collection

Parameters:

coll - elements to be removed from this collection.

Returns:

true if this collection changed as a result of the call

See Also:

Collection.remove(Object), Collection.contains(Object)

retainAll

public boolean retainAll(Collection coll)

Description copied from interface: Collection

Retains only the elements in this collection that are contained in the specified collection (optional operation). In other words, removes from this collection all of its elements that are not contained in the specified collection.

Specified by:

retainAll in interface Collection

Parameters:

coll - elements to be retained in this collection.

Returns:

true if this collection changed as a result of the call

See Also:

Collection.remove(Object), Collection.contains(Object)

clear

public void clear()

Description copied from interface: Collection

Removes all of the elements from this collection (optional operation). This collection will be empty after this method returns unless it throws an exception.

Specified by:

clear in interface Collection