Apache Commons Collections 4.4 · org.apache.commons.collections4.set.MapBackedSet

Modifier and Type	Field and Description
private final V	dummyValue The dummyValue to use
private final Map<E, ? super V>	map The map being used as the backing store
private static final long	serialVersionUID Serialization version

Access	Constructor and Description
private	MapBackedSet(final Map<E, ? super V> the map to decorate, must not be null map, final V the dummy value to use dummyValue) Constructor that wraps (not copies).

Method Summary

Modifier and Type	Method and Description
public boolean	add(final E element to be added to this set obj) Implements java.util.Set.add. Adds the specified element to this set if it is not already present (optional operation).
public boolean	addAll(final Collection<? extends E> collection containing elements to be added to this set coll) Implements java.util.Set.addAll. Adds all of the elements in the specified collection to this set if they're not already present (optional operation).
public void	clear() Implements java.util.Set.clear. Removes all of the elements from this set (optional operation).
public boolean	contains(final Object element whose presence in this set is to be tested obj) Implements java.util.Set.contains. Returns `true` if this set contains the specified element.
public boolean	containsAll(final Collection<?> collection to be checked for containment in this set coll) Implements java.util.Set.containsAll. Returns `true` if this set contains all of the elements of the specified collection.
public boolean	equals(final Object object to be compared for equality with this set obj) Overrides java.lang.Object.equals. Implements java.util.Set.equals. Compares the specified object with this set for equality.
public int	hashCode() Overrides java.lang.Object.hashCode. Implements java.util.Set.hashCode. Returns the hash code value for this set.
public boolean	isEmpty() Implements java.util.Set.isEmpty. Returns `true` if this set contains no elements.
public Iterator<E>	iterator() Implements java.util.Set.iterator. Returns an iterator over the elements in this set.
public static < the element type E, the dummy value type in the map V> MapBackedSet<E, V>	Returns: a new map backed set mapBackedSet(final Map<E, ? super V> the map to decorate, must not be null map) Factory method to create a set from a map.
public static < the element type E, the dummy value type in the map V> MapBackedSet<E, V>	Returns: a new map backed set mapBackedSet(final Map<E, ? super V> the map to decorate, must not be null map, final V the dummy value to use dummyValue) Factory method to create a set from a map.
public boolean	remove(final Object object to be removed from this set, if present obj) Implements java.util.Set.remove. Removes the specified element from this set if it is present (optional operation).
public boolean	removeAll(final Collection<?> collection containing elements to be removed from this set coll) Implements java.util.Set.removeAll. Removes from this set all of its elements that are contained in the specified collection (optional operation).
public boolean	removeIf(Predicate<? super E> a predicate which returns `true` for elements to be removed filter) Overrides default java.util.Collection.removeIf. Removes all of the elements of this collection that satisfy the given predicate.
public boolean	retainAll(final Collection<?> collection containing elements to be retained in this set coll) Implements java.util.Set.retainAll. Retains only the elements in this set that are contained in the specified collection (optional operation).
public int	size() Implements java.util.Set.size. Returns the number of elements in this set (its cardinality).
public Object[]	toArray() Implements java.util.Set.toArray. Returns an array containing all of the elements in this set.
public <T> T[]	toArray(final T[] 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. array) Implements java.util.Set.toArray. Returns an array containing all of the elements in this set; the runtime type of the returned array is that of the specified array.

Inherited from java.lang.Object:: clone finalize getClass notify notifyAll toString wait wait wait

dummyValue	back to summary
private final V dummyValue The dummyValue to use

map	back to summary
private final Map<E, ? super V> map The map being used as the backing store

serialVersionUID	back to summary
private static final long serialVersionUID Serialization version

MapBackedSet	back to summary
private MapBackedSet(final Map<E, ? super V> map, final V dummyValue) Constructor that wraps (not copies). Parameters map:Map<E, ? super V> the map to decorate, must not be null dummyValue:V the dummy value to use Exceptions NullPointerException: if map is null

Method Detail

add back to summary

add	back to summary
public boolean add(final E obj) Implements java.util.Set.add. Doc from java.util.Set.add. Adds the specified element to this set if it is not already present (optional operation). More formally, adds the specified element `e` to this set if the set contains no element `e2` such that `Objects.equals(e, e2)`. If this set already contains the element, the call leaves the set unchanged and returns `false`. In combination with the restriction on constructors, this ensures that sets never contain duplicate elements. The stipulation above does not imply that sets must accept all elements; sets may refuse to add any particular element, including `null`, and throw an exception, as described in the specification for `Collection.add`. Individual set implementations should clearly document any restrictions on the elements that they may contain. Parameters obj:E element to be added to this set Returns:boolean `true` if this set did not already contain the specified element Annotations @Override

public boolean add(final E obj)

Implements java.util.Set.add.

Doc from java.util.Set.add.

Adds the specified element to this set if it is not already present (optional operation). More formally, adds the specified element e to this set if the set contains no element e2 such that Objects.equals(e, e2). If this set already contains the element, the call leaves the set unchanged and returns false. In combination with the restriction on constructors, this ensures that sets never contain duplicate elements.

The stipulation above does not imply that sets must accept all elements; sets may refuse to add any particular element, including null, and throw an exception, as described in the specification for Collection.add. Individual set implementations should clearly document any restrictions on the elements that they may contain.

Parameters

obj:E: element to be added to this set

Returns:boolean

true if this set did not already contain the specified element

Annotations

@Override

addAll back to summary

addAll	back to summary
public boolean addAll(final Collection<? extends E> coll) Implements java.util.Set.addAll. Doc from java.util.Set.addAll. Adds all of the elements in the specified collection to this set if they're not already present (optional operation). If the specified collection is also a set, the `addAll` operation effectively modifies this set so that its value is the union of the two sets. The behavior of this operation is undefined if the specified collection is modified while the operation is in progress. Parameters coll:Collection<? extends E> collection containing elements to be added to this set Returns:boolean `true` if this set changed as a result of the call Annotations @Override

public boolean addAll(final Collection<? extends E> coll)

Implements java.util.Set.addAll.

Doc from java.util.Set.addAll.

Adds all of the elements in the specified collection to this set if they're not already present (optional operation). If the specified collection is also a set, the addAll operation effectively modifies this set so that its value is the union of the two sets. The behavior of this operation is undefined if the specified collection is modified while the operation is in progress.

Parameters

coll:Collection<? extends E>: collection containing elements to be added to this set

Returns:boolean

true if this set changed as a result of the call

Annotations

@Override

clear	back to summary
public void clear() Implements java.util.Set.clear. Doc from java.util.Set.clear. Removes all of the elements from this set (optional operation). The set will be empty after this call returns. Annotations @Override

clear

back to summary

public void clear()

Implements java.util.Set.clear.

Doc from java.util.Set.clear.

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

Annotations

@Override

contains back to summary

contains	back to summary
public boolean contains(final Object obj) Implements java.util.Set.contains. Doc from java.util.Set.contains. Returns `true` if this set contains the specified element. More formally, returns `true` if and only if this set contains an element `e` such that `Objects.equals(o, e)`. Parameters obj:Object element whose presence in this set is to be tested Returns:boolean `true` if this set contains the specified element Annotations @Override

public boolean contains(final Object obj)

Implements java.util.Set.contains.

Doc from java.util.Set.contains.

Returns true if this set contains the specified element. More formally, returns true if and only if this set contains an element e such that Objects.equals(o, e).

Parameters

obj:Object: element whose presence in this set is to be tested

Returns:boolean

true if this set contains the specified element

Annotations

@Override

containsAll back to summary

containsAll	back to summary
public boolean containsAll(final Collection<?> coll) Implements java.util.Set.containsAll. Doc from java.util.Set.containsAll. Returns `true` if this set contains all of the elements of the specified collection. If the specified collection is also a set, this method returns `true` if it is a subset of this set. Parameters coll:Collection<?> collection to be checked for containment in this set Returns:boolean `true` if this set contains all of the elements of the specified collection Annotations @Override

public boolean containsAll(final Collection<?> coll)

Implements java.util.Set.containsAll.

Doc from java.util.Set.containsAll.

Returns true if this set contains all of the elements of the specified collection. If the specified collection is also a set, this method returns true if it is a subset of this set.

Parameters

coll:Collection<?>: collection to be checked for containment in this set

Returns:boolean

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

Annotations

@Override

equals back to summary

equals	back to summary
public boolean equals(final Object obj) Overrides java.lang.Object.equals. Implements java.util.Set.equals. Doc from java.util.Set.equals. 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. Parameters obj:Object object to be compared for equality with this set Returns:boolean `true` if the specified object is equal to this set Annotations @Override

public boolean equals(final Object obj)

Overrides java.lang.Object.equals.

Implements java.util.Set.equals.

Doc from java.util.Set.equals.

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.

Parameters

obj:Object: object to be compared for equality with this set

Returns:boolean

true if the specified object is equal to this set

Annotations

@Override

hashCode back to summary

hashCode	back to summary
public int hashCode() Overrides java.lang.Object.hashCode. Implements java.util.Set.hashCode. Doc from java.util.Set.hashCode. 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 hash code 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 `Object#hashCode`. Returns:int the hash code value for this set Annotations @Override

public int hashCode()

Overrides java.lang.Object.hashCode.

Implements java.util.Set.hashCode.

Doc from java.util.Set.hashCode.

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 hash code 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 Object#hashCode.

Returns:int

the hash code value for this set

Annotations

@Override

isEmpty back to summary

isEmpty	back to summary
public boolean isEmpty() Implements java.util.Set.isEmpty. Doc from java.util.Set.isEmpty. Returns `true` if this set contains no elements. Returns:boolean `true` if this set contains no elements Annotations @Override

public boolean isEmpty()

Implements java.util.Set.isEmpty.

Doc from java.util.Set.isEmpty.

Returns true if this set contains no elements.

Returns:boolean

true if this set contains no elements

Annotations

@Override

iterator	back to summary
public Iterator<E> iterator() Implements java.util.Set.iterator. Doc from java.util.Set.iterator. Returns an iterator over the elements in this set. The elements are returned in no particular order (unless this set is an instance of some class that provides a guarantee). Returns:Iterator<E> an iterator over the elements in this set Annotations @Override

iterator

back to summary

public Iterator<E> iterator()

Implements java.util.Set.iterator.

Doc from java.util.Set.iterator.

Returns an iterator over the elements in this set. The elements are returned in no particular order (unless this set is an instance of some class that provides a guarantee).

Returns:Iterator<E>

an iterator over the elements in this set

Annotations

@Override

mapBackedSet	back to summary
public static <E, V> MapBackedSet<E, V> mapBackedSet(final Map<E, ? super V> map) Factory method to create a set from a map. Parameters <E> the element type <V> the dummy value type in the map map:Map<E, ? super V> the map to decorate, must not be null Returns:MapBackedSet<E, V> a new map backed set Exceptions NullPointerException: if map is null Since 4.0

mapBackedSet

back to summary

public static <E, V> MapBackedSet<E, V> mapBackedSet(final Map<E, ? super V> map)

Factory method to create a set from a map.

Parameters

<E>: the element type
<V>: the dummy value type in the map
map:Map<E, ? super V>: the map to decorate, must not be null

Returns:MapBackedSet<E, V>

a new map backed set

Exceptions

NullPointerException:: if map is null

Since

4.0

mapBackedSet	back to summary
public static <E, V> MapBackedSet<E, V> mapBackedSet(final Map<E, ? super V> map, final V dummyValue) Factory method to create a set from a map. Parameters <E> the element type <V> the dummy value type in the map map:Map<E, ? super V> the map to decorate, must not be null dummyValue:V the dummy value to use Returns:MapBackedSet<E, V> a new map backed set Exceptions NullPointerException: if map is null Since 4.0

mapBackedSet

back to summary

public static <E, V> MapBackedSet<E, V> mapBackedSet(final Map<E, ? super V> map, final V dummyValue)

Factory method to create a set from a map.

Parameters

<E>: the element type
<V>: the dummy value type in the map
map:Map<E, ? super V>: the map to decorate, must not be null
dummyValue:V: the dummy value to use

Returns:MapBackedSet<E, V>

a new map backed set

Exceptions

NullPointerException:: if map is null

Since

4.0

remove back to summary

remove	back to summary
public boolean remove(final Object obj) Implements java.util.Set.remove. Doc from java.util.Set.remove. Removes the specified element from this set if it is present (optional operation). More formally, removes an element `e` such that `Objects.equals(o, e)`, if this set contains such an element. Returns `true` if this set contained the element (or equivalently, if this set changed as a result of the call). (This set will not contain the element once the call returns.) Parameters obj:Object object to be removed from this set, if present Returns:boolean `true` if this set contained the specified element Annotations @Override

public boolean remove(final Object obj)

Implements java.util.Set.remove.

Doc from java.util.Set.remove.

Removes the specified element from this set if it is present (optional operation). More formally, removes an element e such that Objects.equals(o, e), if this set contains such an element. Returns true if this set contained the element (or equivalently, if this set changed as a result of the call). (This set will not contain the element once the call returns.)

Parameters

obj:Object: object to be removed from this set, if present

Returns:boolean

true if this set contained the specified element

Annotations

@Override

removeAll back to summary

removeAll	back to summary
public boolean removeAll(final Collection<?> coll) Implements java.util.Set.removeAll. Doc from java.util.Set.removeAll. 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. Parameters coll:Collection<?> collection containing elements to be removed from this set Returns:boolean `true` if this set changed as a result of the call Annotations @Override

public boolean removeAll(final Collection<?> coll)

Implements java.util.Set.removeAll.

Doc from java.util.Set.removeAll.

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.

Parameters

coll:Collection<?>: collection containing elements to be removed from this set

Returns:boolean

true if this set changed as a result of the call

Annotations

@Override

removeIf back to summary

removeIf	back to summary
public boolean removeIf(Predicate<? super E> filter) Overrides default java.util.Collection.removeIf. Doc from java.util.Collection.removeIf. Removes all of the elements of this collection that satisfy the given predicate. Errors or runtime exceptions thrown during iteration or by the predicate are relayed to the caller. Parameters filter:Predicate<? super E> a predicate which returns `true` for elements to be removed Returns:boolean `true` if any elements were removed Annotations @Override Since 4.4

public boolean removeIf(Predicate<? super E> filter)

Overrides default java.util.Collection.removeIf.

Doc from java.util.Collection.removeIf.

Removes all of the elements of this collection that satisfy the given predicate. Errors or runtime exceptions thrown during iteration or by the predicate are relayed to the caller.

Parameters

filter:Predicate<? super E>: a predicate which returns true for elements to be removed

Returns:boolean

true if any elements were removed

Annotations

@Override

Since

4.4

retainAll back to summary

retainAll	back to summary
public boolean retainAll(final Collection<?> coll) Implements java.util.Set.retainAll. Doc from java.util.Set.retainAll. Retains only the elements in this set that are contained in the specified collection (optional operation). In other words, removes from this set all of its elements that are not contained in the specified collection. If the specified collection is also a set, this operation effectively modifies this set so that its value is the intersection of the two sets. Parameters coll:Collection<?> collection containing elements to be retained in this set Returns:boolean `true` if this set changed as a result of the call Annotations @Override

public boolean retainAll(final Collection<?> coll)

Implements java.util.Set.retainAll.

Doc from java.util.Set.retainAll.

Retains only the elements in this set that are contained in the specified collection (optional operation). In other words, removes from this set all of its elements that are not contained in the specified collection. If the specified collection is also a set, this operation effectively modifies this set so that its value is the intersection of the two sets.

Parameters

coll:Collection<?>: collection containing elements to be retained in this set

Returns:boolean

true if this set changed as a result of the call

Annotations

@Override

size back to summary

size	back to summary
public int size() Implements java.util.Set.size. Doc from java.util.Set.size. Returns the number of elements in this set (its cardinality). If this set contains more than `Integer.MAX_VALUE` elements, returns `Integer.MAX_VALUE`. Returns:int the number of elements in this set (its cardinality) Annotations @Override

public int size()

Implements java.util.Set.size.

Doc from java.util.Set.size.

Returns the number of elements in this set (its cardinality). If this set contains more than Integer.MAX_VALUE elements, returns Integer.MAX_VALUE.

Returns:int

the number of elements in this set (its cardinality)

Annotations

@Override

toArray	back to summary
public Object[] toArray() Implements java.util.Set.toArray. Doc from java.util.Set.toArray. Returns an array containing all of the elements in this set. 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. The returned array will be "safe" in that no references to it are maintained by this set. (In other words, this method must allocate a new array even if this set 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. Returns:Object[] an array containing all the elements in this set Annotations @Override

toArray

back to summary

public Object[] toArray()

Implements java.util.Set.toArray.

Doc from java.util.Set.toArray.

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

The returned array will be "safe" in that no references to it are maintained by this set. (In other words, this method must allocate a new array even if this set 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.

Returns:Object[]

an array containing all the elements in this set

Annotations

@Override

toArray back to summary

toArray	back to summary
public <T> T[] toArray(final T[] array) Implements java.util.Set.toArray. Doc from java.util.Set.toArray. 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 `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()`. Parameters <T> Doc from java.util.Collection.toArray. the component type of the array to contain the collection array:T[] 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. Returns:T[] an array containing all the elements in this set Annotations @Override

public <T> T[] toArray(final T[] array)

Implements java.util.Set.toArray.

Doc from java.util.Set.toArray.

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 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().

Parameters

<T>: Doc from java.util.Collection.toArray. the component type of the array to contain the collection
array:T[]: 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.

Returns:T[]

an array containing all the elements in this set

Annotations

@Override

public final Class MapBackedSet<E, V>

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