com.google.common.collect

Class ForwardingMap.StandardKeySet

java.lang.Object

java.util.AbstractCollection<E>

java.util.AbstractSet<E>

com.google.common.collect.ForwardingMap.StandardKeySet

All Implemented Interfaces:

Iterable<K>, Collection<K>, Set<K>

Enclosing class:

ForwardingMap<K,V>

@Beta
protected class ForwardingMap.StandardKeySet
extends AbstractSet<E>

A sensible implementation of Map.keySet() in terms of the following methods: ForwardingMap.clear(), ForwardingMap.containsKey(java.lang.Object), ForwardingMap.isEmpty(), ForwardingMap.remove(java.lang.Object), ForwardingMap.size(), and the Set.iterator() method of ForwardingMap.entrySet(). In many cases, you may wish to override ForwardingMap.keySet() to forward to this implementation or a subclass thereof.

Since:

10.0

Constructor Summary

Constructors

Constructor and Description
StandardKeySet() Constructor for use by subclasses.

Method Summary

Modifier and Type	Method and Description
void	clear() Removes all of the elements from this collection (optional operation).
boolean	contains(Object o) Returns true if this collection contains the specified element.
boolean	isEmpty() Returns true if this collection contains no elements.
Iterator<K>	iterator() Returns an iterator over the elements contained in this collection.
boolean	remove(Object o) Removes a single instance of the specified element from this collection, if it is present (optional operation).
boolean	removeAll(Collection<?> c) Removes from this set all of its elements that are contained in the specified collection (optional operation).
boolean	retainAll(Collection<?> c) Retains only the elements in this collection that are contained in the specified collection (optional operation).
int	size() Returns the number of elements in this collection.

Methods inherited from class java.util.AbstractSet

equals, hashCode

Methods inherited from class java.util.AbstractCollection

add, addAll, containsAll, toArray, toArray, toString

Methods inherited from class java.lang.Object

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

Methods inherited from interface java.util.Set

add, addAll, containsAll, spliterator, toArray, toArray

Methods inherited from interface java.util.Collection

parallelStream, removeIf, stream

Methods inherited from interface java.lang.Iterable

forEach

Constructor Detail

StandardKeySet

public StandardKeySet()

Constructor for use by subclasses.

Method Detail

iterator

public Iterator<K> iterator()

Description copied from class: java.util.AbstractCollection

Returns an iterator over the elements contained in this collection.

Specified by:

iterator in interface Iterable<K>

Specified by:

iterator in interface Collection<K>

Specified by:

iterator in interface Set<K>

Specified by:

iterator in class AbstractCollection<K>

Returns:

an iterator over the elements contained in this collection

size

public int size()

Description copied from interface: java.util.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<K>

Specified by:

size in interface Set<K>

Specified by:

size in class AbstractCollection<K>

Returns:

the number of elements in this collection

isEmpty

public boolean isEmpty()

Description copied from class: java.util.AbstractCollection

Returns true if this collection contains no elements.

This implementation returns size() == 0.

Specified by:

isEmpty in interface Collection<K>

Specified by:

isEmpty in interface Set<K>

Overrides:

isEmpty in class AbstractCollection<K>

Returns:

true if this collection contains no elements

contains

public boolean contains(Object o)

Description copied from class: java.util.AbstractCollection

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)).

This implementation iterates over the elements in the collection, checking each element in turn for equality with the specified element.

Specified by:

contains in interface Collection<K>

Specified by:

contains in interface Set<K>

Overrides:

contains in class AbstractCollection<K>

Parameters:

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

Returns:

true if this collection contains the specified element

remove

public boolean remove(Object o)

Description copied from class: java.util.AbstractCollection

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).

This implementation iterates over the collection looking for the specified element. If it finds the element, it removes the element from the collection using the iterator's remove method.

Note that this implementation throws an UnsupportedOperationException if the iterator returned by this collection's iterator method does not implement the remove method and this collection contains the specified object.

Specified by:

remove in interface Collection<K>

Specified by:

remove in interface Set<K>

Overrides:

remove in class AbstractCollection<K>

Parameters:

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

Returns:

true if an element was removed as a result of this call

clear

public void clear()

Description copied from class: java.util.AbstractCollection

Removes all of the elements from this collection (optional operation). The collection will be empty after this method returns.

This implementation iterates over this collection, removing each element using the Iterator.remove operation. Most implementations will probably choose to override this method for efficiency.

Note that this implementation will throw an UnsupportedOperationException if the iterator returned by this collection's iterator method does not implement the remove method and this collection is non-empty.

Specified by:

clear in interface Collection<K>

Specified by:

clear in interface Set<K>

Overrides:

clear in class AbstractCollection<K>

removeAll

public boolean removeAll(Collection<?> c)

Description copied from class: java.util.AbstractSet

Removes from this set all of its elements that are contained in the specified collection (optional operation). If the specified collection is also a set, this operation effectively modifies this set so that its value is the asymmetric set difference of the two sets.

This implementation determines which is the smaller of this set and the specified collection, by invoking the size method on each. If this set has fewer elements, then the implementation iterates over this set, checking each element returned by the iterator in turn to see if it is contained in the specified collection. If it is so contained, it is removed from this set with the iterator's remove method. If the specified collection has fewer elements, then the implementation iterates over the specified collection, removing from this set each element returned by the iterator, using this set's remove method.

Note that this implementation will throw an UnsupportedOperationException if the iterator returned by the iterator method does not implement the remove method.

Specified by:

removeAll in interface Collection<E>

Specified by:

removeAll in interface Set<E>

Overrides:

removeAll in class AbstractSet<E>

Parameters:

c - collection containing elements to be removed from this set

Returns:

true if this set changed as a result of the call

See Also:

AbstractCollection.remove(Object), AbstractCollection.contains(Object)

retainAll

public boolean retainAll(Collection<?> c)

Description copied from class: java.util.AbstractCollection

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.

This implementation iterates over this collection, checking each element returned by the iterator in turn to see if it's contained in the specified collection. If it's not so contained, it's removed from this collection with the iterator's remove method.

Note that this implementation will throw an UnsupportedOperationException if the iterator returned by the iterator method does not implement the remove method and this collection contains one or more elements not present in the specified collection.

Specified by:

retainAll in interface Collection<E>

Specified by:

retainAll in interface Set<E>

Overrides:

retainAll in class AbstractCollection<E>

Parameters:

c - collection containing elements to be retained in this collection

Returns:

true if this collection changed as a result of the call

See Also:

AbstractCollection.remove(Object), AbstractCollection.contains(Object)