代码语言：javascript复制
/**
* Returns a dynamically typesafe view of the specified sorted map.
* Any attempt to insert a mapping whose key or value have the wrong
* type will result in an immediate {@link ClassCastException}.
* Similarly, any attempt to modify the value currently associated with
* a key will result in an immediate {@link ClassCastException},
* whether the modification is attempted directly through the map
* itself, or through a {@link Map.Entry} instance obtained from the
* map's {@link Map#entrySet() entry set} view.
*
* <p>Assuming a map contains no incorrectly typed keys or values
* prior to the time a dynamically typesafe view is generated, and
* that all subsequent access to the map takes place through the view
* (or one of its collection views), it is <i>guaranteed</i> that the
* map cannot contain an incorrectly typed key or value.
*
* <p>A discussion of the use of dynamically typesafe views may be
* found in the documentation for the {@link #checkedCollection
* checkedCollection} method.
*
* <p>The returned map will be serializable if the specified map is
* serializable.
*
* <p>Since {@code null} is considered to be a value of any reference
* type, the returned map permits insertion of null keys or values
* whenever the backing map does.
*
* @param <K> the class of the map keys
* @param <V> the class of the map values
* @param m the map for which a dynamically typesafe view is to be
* returned
* @param keyType the type of key that {@code m} is permitted to hold
* @param valueType the type of value that {@code m} is permitted to hold
* @return a dynamically typesafe view of the specified map
* @since 1.5
*/
public static <K,V> SortedMap<K,V> checkedSortedMap(SortedMap<K, V> m,
Class<K> keyType,
Class<V> valueType) {
return new CheckedSortedMap<>(m, keyType, valueType);
}
/**
* @serial include
*/
static class CheckedSortedMap<K,V> extends CheckedMap<K,V>
implements SortedMap<K,V>, Serializable
{
private static final long serialVersionUID = 1599671320688067438L;
private final SortedMap<K, V> sm;
CheckedSortedMap(SortedMap<K, V> m,
Class<K> keyType, Class<V> valueType) {
super(m, keyType, valueType);
sm = m;
}
public Comparator<? super K> comparator() { return sm.comparator(); }
public K firstKey() { return sm.firstKey(); }
public K lastKey() { return sm.lastKey(); }
public SortedMap<K,V> subMap(K fromKey, K toKey) {
return checkedSortedMap(sm.subMap(fromKey, toKey),
keyType, valueType);
}
public SortedMap<K,V> headMap(K toKey) {
return checkedSortedMap(sm.headMap(toKey), keyType, valueType);
}
public SortedMap<K,V> tailMap(K fromKey) {
return checkedSortedMap(sm.tailMap(fromKey), keyType, valueType);
}
}
/**
* Returns a dynamically typesafe view of the specified navigable map.
* Any attempt to insert a mapping whose key or value have the wrong
* type will result in an immediate {@link ClassCastException}.
* Similarly, any attempt to modify the value currently associated with
* a key will result in an immediate {@link ClassCastException},
* whether the modification is attempted directly through the map
* itself, or through a {@link Map.Entry} instance obtained from the
* map's {@link Map#entrySet() entry set} view.
*
* <p>Assuming a map contains no incorrectly typed keys or values
* prior to the time a dynamically typesafe view is generated, and
* that all subsequent access to the map takes place through the view
* (or one of its collection views), it is <em>guaranteed</em> that the
* map cannot contain an incorrectly typed key or value.
*
* <p>A discussion of the use of dynamically typesafe views may be
* found in the documentation for the {@link #checkedCollection
* checkedCollection} method.
*
* <p>The returned map will be serializable if the specified map is
* serializable.
*
* <p>Since {@code null} is considered to be a value of any reference
* type, the returned map permits insertion of null keys or values
* whenever the backing map does.
*
* @param <K> type of map keys
* @param <V> type of map values
* @param m the map for which a dynamically typesafe view is to be
* returned
* @param keyType the type of key that {@code m} is permitted to hold
* @param valueType the type of value that {@code m} is permitted to hold
* @return a dynamically typesafe view of the specified map
* @since 1.8
*/
public static <K,V> NavigableMap<K,V> checkedNavigableMap(NavigableMap<K, V> m,
Class<K> keyType,
Class<V> valueType) {
return new CheckedNavigableMap<>(m, keyType, valueType);
}
/**
* @serial include
*/
static class CheckedNavigableMap<K,V> extends CheckedSortedMap<K,V>
implements NavigableMap<K,V>, Serializable
{
private static final long serialVersionUID = -4852462692372534096L;
private final NavigableMap<K, V> nm;
CheckedNavigableMap(NavigableMap<K, V> m,
Class<K> keyType, Class<V> valueType) {
super(m, keyType, valueType);
nm = m;
}
public Comparator<? super K> comparator() { return nm.comparator(); }
public K firstKey() { return nm.firstKey(); }
public K lastKey() { return nm.lastKey(); }
public Entry<K, V> lowerEntry(K key) {
Entry<K,V> lower = nm.lowerEntry(key);
return (null != lower)
? new CheckedMap.CheckedEntrySet.CheckedEntry<>(lower, valueType)
: null;
}
public K lowerKey(K key) { return nm.lowerKey(key); }
public Entry<K, V> floorEntry(K key) {
Entry<K,V> floor = nm.floorEntry(key);
return (null != floor)
? new CheckedMap.CheckedEntrySet.CheckedEntry<>(floor, valueType)
: null;
}
public K floorKey(K key) { return nm.floorKey(key); }
public Entry<K, V> ceilingEntry(K key) {
Entry<K,V> ceiling = nm.ceilingEntry(key);
return (null != ceiling)
? new CheckedMap.CheckedEntrySet.CheckedEntry<>(ceiling, valueType)
: null;
}
public K ceilingKey(K key) { return nm.ceilingKey(key); }
public Entry<K, V> higherEntry(K key) {
Entry<K,V> higher = nm.higherEntry(key);
return (null != higher)
? new CheckedMap.CheckedEntrySet.CheckedEntry<>(higher, valueType)
: null;
}
public K higherKey(K key) { return nm.higherKey(key); }
public Entry<K, V> firstEntry() {
Entry<K,V> first = nm.firstEntry();
return (null != first)
? new CheckedMap.CheckedEntrySet.CheckedEntry<>(first, valueType)
: null;
}
public Entry<K, V> lastEntry() {
Entry<K,V> last = nm.lastEntry();
return (null != last)
? new CheckedMap.CheckedEntrySet.CheckedEntry<>(last, valueType)
: null;
}
public Entry<K, V> pollFirstEntry() {
Entry<K,V> entry = nm.pollFirstEntry();
return (null == entry)
? null
: new CheckedMap.CheckedEntrySet.CheckedEntry<>(entry, valueType);
}
public Entry<K, V> pollLastEntry() {
Entry<K,V> entry = nm.pollLastEntry();
return (null == entry)
? null
: new CheckedMap.CheckedEntrySet.CheckedEntry<>(entry, valueType);
}
public NavigableMap<K, V> descendingMap() {
return checkedNavigableMap(nm.descendingMap(), keyType, valueType);
}
public NavigableSet<K> keySet() {
return navigableKeySet();
}
public NavigableSet<K> navigableKeySet() {
return checkedNavigableSet(nm.navigableKeySet(), keyType);
}
public NavigableSet<K> descendingKeySet() {
return checkedNavigableSet(nm.descendingKeySet(), keyType);
}
@Override
public NavigableMap<K,V> subMap(K fromKey, K toKey) {
return checkedNavigableMap(nm.subMap(fromKey, true, toKey, false),
keyType, valueType);
}
@Override
public NavigableMap<K,V> headMap(K toKey) {
return checkedNavigableMap(nm.headMap(toKey, false), keyType, valueType);
}
@Override
public NavigableMap<K,V> tailMap(K fromKey) {
return checkedNavigableMap(nm.tailMap(fromKey, true), keyType, valueType);
}
public NavigableMap<K, V> subMap(K fromKey, boolean fromInclusive, K toKey, boolean toInclusive) {
return checkedNavigableMap(nm.subMap(fromKey, fromInclusive, toKey, toInclusive), keyType, valueType);
}
public NavigableMap<K, V> headMap(K toKey, boolean inclusive) {
return checkedNavigableMap(nm.headMap(toKey, inclusive), keyType, valueType);
}
public NavigableMap<K, V> tailMap(K fromKey, boolean inclusive) {
return checkedNavigableMap(nm.tailMap(fromKey, inclusive), keyType, valueType);
}
}
// Empty collections
/**
* Returns an iterator that has no elements. More precisely,
*
* <ul>
* <li>{@link Iterator#hasNext hasNext} always returns {@code
* false}.</li>
* <li>{@link Iterator#next next} always throws {@link
* NoSuchElementException}.</li>
* <li>{@link Iterator#remove remove} always throws {@link
* IllegalStateException}.</li>
* </ul>
*
* <p>Implementations of this method are permitted, but not
* required, to return the same object from multiple invocations.
*
* @param <T> type of elements, if there were any, in the iterator
* @return an empty iterator
* @since 1.7
*/
@SuppressWarnings("unchecked")
public static <T> Iterator<T> emptyIterator() {
return (Iterator<T>) EmptyIterator.EMPTY_ITERATOR;
}
private static class EmptyIterator<E> implements Iterator<E> {
static final EmptyIterator<Object> EMPTY_ITERATOR
= new EmptyIterator<>();
public boolean hasNext() { return false; }
public E next() { throw new NoSuchElementException(); }
public void remove() { throw new IllegalStateException(); }
@Override
public void forEachRemaining(Consumer<? super E> action) {
Objects.requireNonNull(action);
}
}
/**
* Returns a list iterator that has no elements. More precisely,
*
* <ul>
* <li>{@link Iterator#hasNext hasNext} and {@link
* ListIterator#hasPrevious hasPrevious} always return {@code
* false}.</li>
* <li>{@link Iterator#next next} and {@link ListIterator#previous
* previous} always throw {@link NoSuchElementException}.</li>
* <li>{@link Iterator#remove remove} and {@link ListIterator#set
* set} always throw {@link IllegalStateException}.</li>
* <li>{@link ListIterator#add add} always throws {@link
* UnsupportedOperationException}.</li>
* <li>{@link ListIterator#nextIndex nextIndex} always returns
* {@code 0}.</li>
* <li>{@link ListIterator#previousIndex previousIndex} always
* returns {@code -1}.</li>
* </ul>
*
* <p>Implementations of this method are permitted, but not
* required, to return the same object from multiple invocations.
*
* @param <T> type of elements, if there were any, in the iterator
* @return an empty list iterator
* @since 1.7
*/
@SuppressWarnings("unchecked")
public static <T> ListIterator<T> emptyListIterator() {
return (ListIterator<T>) EmptyListIterator.EMPTY_ITERATOR;
}
private static class EmptyListIterator<E>
extends EmptyIterator<E>
implements ListIterator<E>
{
static final EmptyListIterator<Object> EMPTY_ITERATOR
= new EmptyListIterator<>();
public boolean hasPrevious() { return false; }
public E previous() { throw new NoSuchElementException(); }
public int nextIndex() { return 0; }
public int previousIndex() { return -1; }
public void set(E e) { throw new IllegalStateException(); }
public void add(E e) { throw new UnsupportedOperationException(); }
}
/**
* Returns an enumeration that has no elements. More precisely,
*
* <ul>
* <li>{@link Enumeration#hasMoreElements hasMoreElements} always
* returns {@code false}.</li>
* <li> {@link Enumeration#nextElement nextElement} always throws
* {@link NoSuchElementException}.</li>
* </ul>
*
* <p>Implementations of this method are permitted, but not
* required, to return the same object from multiple invocations.
*
* @param <T> the class of the objects in the enumeration
* @return an empty enumeration
* @since 1.7
*/
@SuppressWarnings("unchecked")
public static <T> Enumeration<T> emptyEnumeration() {
return (Enumeration<T>) EmptyEnumeration.EMPTY_ENUMERATION;
}
private static class EmptyEnumeration<E> implements Enumeration<E> {
static final EmptyEnumeration<Object> EMPTY_ENUMERATION
= new EmptyEnumeration<>();
public boolean hasMoreElements() { return false; }
public E nextElement() { throw new NoSuchElementException(); }
}
/**
* The empty set (immutable). This set is serializable.
*
* @see #emptySet()
*/
@SuppressWarnings("rawtypes")
public static final Set EMPTY_SET = new EmptySet<>();
/**
* Returns an empty set (immutable). This set is serializable.
* Unlike the like-named field, this method is parameterized.
*
* <p>This example illustrates the type-safe way to obtain an empty set:
* <pre>
* Set<String> s = Collections.emptySet();
* </pre>
* @implNote Implementations of this method need not create a separate
* {@code Set} object for each call. Using this method is likely to have
* comparable cost to using the like-named field. (Unlike this method, the
* field does not provide type safety.)
*
* @param <T> the class of the objects in the set
* @return the empty set
*
* @see #EMPTY_SET
* @since 1.5
*/
@SuppressWarnings("unchecked")
public static final <T> Set<T> emptySet() {
return (Set<T>) EMPTY_SET;
}
/**
* @serial include
*/
private static class EmptySet<E>
extends AbstractSet<E>
implements Serializable
{
private static final long serialVersionUID = 1582296315990362920L;
public Iterator<E> iterator() { return emptyIterator(); }
public int size() {return 0;}
public boolean isEmpty() {return true;}
public boolean contains(Object obj) {return false;}
public boolean containsAll(Collection<?> c) { return c.isEmpty(); }
public Object[] toArray() { return new Object[0]; }
public <T> T[] toArray(T[] a) {
if (a.length > 0)
a[0] = null;
return a;
}
// Override default methods in Collection
@Override
public void forEach(Consumer<? super E> action) {
Objects.requireNonNull(action);
}
@Override
public boolean removeIf(Predicate<? super E> filter) {
Objects.requireNonNull(filter);
return false;
}
@Override
public Spliterator<E> spliterator() { return Spliterators.emptySpliterator(); }
// Preserves singleton property
private Object readResolve() {
return EMPTY_SET;
}
}
/**
* Returns an empty sorted set (immutable). This set is serializable.
*
* <p>This example illustrates the type-safe way to obtain an empty
* sorted set:
* <pre> {@code
* SortedSet<String> s = Collections.emptySortedSet();
* }</pre>
*
* @implNote Implementations of this method need not create a separate
* {@code SortedSet} object for each call.
*
* @param <E> type of elements, if there were any, in the set
* @return the empty sorted set
* @since 1.8
*/
@SuppressWarnings("unchecked")
public static <E> SortedSet<E> emptySortedSet() {
return (SortedSet<E>) UnmodifiableNavigableSet.EMPTY_NAVIGABLE_SET;
}
/**
* Returns an empty navigable set (immutable). This set is serializable.
*
* <p>This example illustrates the type-safe way to obtain an empty
* navigable set:
* <pre> {@code
* NavigableSet<String> s = Collections.emptyNavigableSet();
* }</pre>
*
* @implNote Implementations of this method need not
* create a separate {@code NavigableSet} object for each call.
*
* @param <E> type of elements, if there were any, in the set
* @return the empty navigable set
* @since 1.8
*/
@SuppressWarnings("unchecked")
public static <E> NavigableSet<E> emptyNavigableSet() {
return (NavigableSet<E>) UnmodifiableNavigableSet.EMPTY_NAVIGABLE_SET;
}
/**
* The empty list (immutable). This list is serializable.
*
* @see #emptyList()
*/
@SuppressWarnings("rawtypes")
public static final List EMPTY_LIST = new EmptyList<>();
/**
* Returns an empty list (immutable). This list is serializable.
*
* <p>This example illustrates the type-safe way to obtain an empty list:
* <pre>
* List<String> s = Collections.emptyList();
* </pre>
*
* @implNote
* Implementations of this method need not create a separate <tt>List</tt>
* object for each call. Using this method is likely to have comparable
* cost to using the like-named field. (Unlike this method, the field does
* not provide type safety.)
*
* @param <T> type of elements, if there were any, in the list
* @return an empty immutable list
*
* @see #EMPTY_LIST
* @since 1.5
*/
@SuppressWarnings("unchecked")
public static final <T> List<T> emptyList() {
return (List<T>) EMPTY_LIST;
}
/**
* @serial include
*/
private static class EmptyList<E>
extends AbstractList<E>
implements RandomAccess, Serializable {
private static final long serialVersionUID = 8842843931221139166L;
public Iterator<E> iterator() {
return emptyIterator();
}
public ListIterator<E> listIterator() {
return emptyListIterator();
}
public int size() {return 0;}
public boolean isEmpty() {return true;}
public boolean contains(Object obj) {return false;}
public boolean containsAll(Collection<?> c) { return c.isEmpty(); }
public Object[] toArray() { return new Object[0]; }
public <T> T[] toArray(T[] a) {
if (a.length > 0)
a[0] = null;
return a;
}
public E get(int index) {
throw new IndexOutOfBoundsException("Index: " index);
}
public boolean equals(Object o) {
return (o instanceof List) && ((List<?>)o).isEmpty();
}
public int hashCode() { return 1; }
@Override
public boolean removeIf(Predicate<? super E> filter) {
Objects.requireNonNull(filter);
return false;
}
@Override
public void replaceAll(UnaryOperator<E> operator) {
Objects.requireNonNull(operator);
}
@Override
public void sort(Comparator<? super E> c) {
}
// Override default methods in Collection
@Override
public void forEach(Consumer<? super E> action) {
Objects.requireNonNull(action);
}
@Override
public Spliterator<E> spliterator() { return Spliterators.emptySpliterator(); }
// Preserves singleton property
private Object readResolve() {
return EMPTY_LIST;
}
}
/**
* The empty map (immutable). This map is serializable.
*
* @see #emptyMap()
* @since 1.3
*/
@SuppressWarnings("rawtypes")
public static final Map EMPTY_MAP = new EmptyMap<>();
/**
* Returns an empty map (immutable). This map is serializable.
*
* <p>This example illustrates the type-safe way to obtain an empty map:
* <pre>
* Map<String, Date> s = Collections.emptyMap();
* </pre>
* @implNote Implementations of this method need not create a separate
* {@code Map} object for each call. Using this method is likely to have
* comparable cost to using the like-named field. (Unlike this method, the
* field does not provide type safety.)
*
* @param <K> the class of the map keys
* @param <V> the class of the map values
* @return an empty map
* @see #EMPTY_MAP
* @since 1.5
*/
@SuppressWarnings("unchecked")
public static final <K,V> Map<K,V> emptyMap() {
return (Map<K,V>) EMPTY_MAP;
}
/**
* Returns an empty sorted map (immutable). This map is serializable.
*
* <p>This example illustrates the type-safe way to obtain an empty map:
* <pre> {@code
* SortedMap<String, Date> s = Collections.emptySortedMap();
* }</pre>
*
* @implNote Implementations of this method need not create a separate
* {@code SortedMap} object for each call.
*
* @param <K> the class of the map keys
* @param <V> the class of the map values
* @return an empty sorted map
* @since 1.8
*/
@SuppressWarnings("unchecked")
public static final <K,V> SortedMap<K,V> emptySortedMap() {
return (SortedMap<K,V>) UnmodifiableNavigableMap.EMPTY_NAVIGABLE_MAP;
}
/**
* Returns an empty navigable map (immutable). This map is serializable.
*
* <p>This example illustrates the type-safe way to obtain an empty map:
* <pre> {@code
* NavigableMap<String, Date> s = Collections.emptyNavigableMap();
* }</pre>
*
* @implNote Implementations of this method need not create a separate
* {@code NavigableMap} object for each call.
*
* @param <K> the class of the map keys
* @param <V> the class of the map values
* @return an empty navigable map
* @since 1.8
*/
@SuppressWarnings("unchecked")
public static final <K,V> NavigableMap<K,V> emptyNavigableMap() {
return (NavigableMap<K,V>) UnmodifiableNavigableMap.EMPTY_NAVIGABLE_MAP;
}
/**
* @serial include
*/
private static class EmptyMap<K,V>
extends AbstractMap<K,V>
implements Serializable
{
private static final long serialVersionUID = 6428348081105594320L;
public int size() {return 0;}
public boolean isEmpty() {return true;}
public boolean containsKey(Object key) {return false;}
public boolean containsValue(Object value) {return false;}
public V get(Object key) {return null;}
public Set<K> keySet() {return emptySet();}
public Collection<V> values() {return emptySet();}
public Set<Map.Entry<K,V>> entrySet() {return emptySet();}
public boolean equals(Object o) {
return (o instanceof Map) && ((Map<?,?>)o).isEmpty();
}
public int hashCode() {return 0;}
// Override default methods in Map
@Override
@SuppressWarnings("unchecked")
public V getOrDefault(Object k, V defaultValue) {
return defaultValue;
}
@Override
public void forEach(BiConsumer<? super K, ? super V> action) {
Objects.requireNonNull(action);
}
@Override
public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) {
Objects.requireNonNull(function);
}
@Override
public V putIfAbsent(K key, V value) {
throw new UnsupportedOperationException();
}
@Override
public boolean remove(Object key, Object value) {
throw new UnsupportedOperationException();
}
@Override
public boolean replace(K key, V oldValue, V newValue) {
throw new UnsupportedOperationException();
}
@Override
public V replace(K key, V value) {
throw new UnsupportedOperationException();
}
@Override
public V computeIfAbsent(K key,
Function<? super K, ? extends V> mappingFunction) {
throw new UnsupportedOperationException();
}
@Override
public V computeIfPresent(K key,
BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
throw new UnsupportedOperationException();
}
@Override
public V compute(K key,
BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
throw new UnsupportedOperationException();
}
@Override
public V merge(K key, V value,
BiFunction<? super V, ? super V, ? extends V> remappingFunction) {
throw new UnsupportedOperationException();
}
// Preserves singleton property
private Object readResolve() {
return EMPTY_MAP;
}
}
// Singleton collections
/**
* Returns an immutable set containing only the specified object.
* The returned set is serializable.
*
* @param <T> the class of the objects in the set
* @param o the sole object to be stored in the returned set.
* @return an immutable set containing only the specified object.
*/
public static <T> Set<T> singleton(T o) {
return new SingletonSet<>(o);
}
static <E> Iterator<E> singletonIterator(final E e) {
return new Iterator<E>() {
private boolean hasNext = true;
public boolean hasNext() {
return hasNext;
}
public E next() {
if (hasNext) {
hasNext = false;
return e;
}
throw new NoSuchElementException();
}
public void remove() {
throw new UnsupportedOperationException();
}
@Override
public void forEachRemaining(Consumer<? super E> action) {
Objects.requireNonNull(action);
if (hasNext) {
action.accept(e);
hasNext = false;
}
}
};
}
/**
* Creates a {@code Spliterator} with only the specified element
*
* @param <T> Type of elements
* @return A singleton {@code Spliterator}
*/
static <T> Spliterator<T> singletonSpliterator(final T element) {
return new Spliterator<T>() {
long est = 1;
@Override
public Spliterator<T> trySplit() {
return null;
}
@Override
public boolean tryAdvance(Consumer<? super T> consumer) {
Objects.requireNonNull(consumer);
if (est > 0) {
est--;
consumer.accept(element);
return true;
}
return false;
}
@Override
public void forEachRemaining(Consumer<? super T> consumer) {
tryAdvance(consumer);
}
@Override
public long estimateSize() {
return est;
}
@Override
public int characteristics() {
int value = (element != null) ? Spliterator.NONNULL : 0;
return value | Spliterator.SIZED | Spliterator.SUBSIZED | Spliterator.IMMUTABLE |
Spliterator.DISTINCT | Spliterator.ORDERED;
}
};
}
/**
* @serial include
*/
private static class SingletonSet<E>
extends AbstractSet<E>
implements Serializable
{
private static final long serialVersionUID = 3193687207550431679L;
private final E element;
SingletonSet(E e) {element = e;}
public Iterator<E> iterator() {
return singletonIterator(element);
}
public int size() {return 1;}
public boolean contains(Object o) {return eq(o, element);}
// Override default methods for Collection
@Override
public void forEach(Consumer<? super E> action) {
action.accept(element);
}
@Override
public Spliterator<E> spliterator() {
return singletonSpliterator(element);
}
@Override
public boolean removeIf(Predicate<? super E> filter) {
throw new UnsupportedOperationException();
}
}
/**
* Returns an immutable list containing only the specified object.
* The returned list is serializable.
*
* @param <T> the class of the objects in the list
* @param o the sole object to be stored in the returned list.
* @return an immutable list containing only the specified object.
* @since 1.3
*/
public static <T> List<T> singletonList(T o) {
return new SingletonList<>(o);
}
/**
* @serial include
*/
private static class SingletonList<E>
extends AbstractList<E>
implements RandomAccess, Serializable {
private static final long serialVersionUID = 3093736618740652951L;
private final E element;
SingletonList(E obj) {element = obj;}
public Iterator<E> iterator() {
return singletonIterator(element);
}
public int size() {return 1;}
public boolean contains(Object obj) {return eq(obj, element);}
public E get(int index) {
if (index != 0)
throw new IndexOutOfBoundsException("Index: " index ", Size: 1");
return element;
}
// Override default methods for Collection
@Override
public void forEach(Consumer<? super E> action) {
action.accept(element);
}
@Override
public boolean removeIf(Predicate<? super E> filter) {
throw new UnsupportedOperationException();
}
@Override
public void replaceAll(UnaryOperator<E> operator) {
throw new UnsupportedOperationException();
}
@Override
public void sort(Comparator<? super E> c) {
}
@Override
public Spliterator<E> spliterator() {
return singletonSpliterator(element);
}
}
/**
* Returns an immutable map, mapping only the specified key to the
* specified value. The returned map is serializable.
*
* @param <K> the class of the map keys
* @param <V> the class of the map values
* @param key the sole key to be stored in the returned map.
* @param value the value to which the returned map maps <tt>key</tt>.
* @return an immutable map containing only the specified key-value
* mapping.
* @since 1.3
*/
public static <K,V> Map<K,V> singletonMap(K key, V value) {
return new SingletonMap<>(key, value);
}
/**
* @serial include
*/
private static class SingletonMap<K,V>
extends AbstractMap<K,V>
implements Serializable {
private static final long serialVersionUID = -6979724477215052911L;
private final K k;
private final V v;
SingletonMap(K key, V value) {
k = key;
v = value;
}
public int size() {return 1;}
public boolean isEmpty() {return false;}
public boolean containsKey(Object key) {return eq(key, k);}
public boolean containsValue(Object value) {return eq(value, v);}
public V get(Object key) {return (eq(key, k) ? v : null);}
private transient Set<K> keySet;
private transient Set<Map.Entry<K,V>> entrySet;
private transient Collection<V> values;
public Set<K> keySet() {
if (keySet==null)
keySet = singleton(k);
return keySet;
}
public Set<Map.Entry<K,V>> entrySet() {
if (entrySet==null)
entrySet = Collections.<Map.Entry<K,V>>singleton(
new SimpleImmutableEntry<>(k, v));
return entrySet;
}
public Collection<V> values() {
if (values==null)
values = singleton(v);
return values;
}
// Override default methods in Map
@Override
public V getOrDefault(Object key, V defaultValue) {
return eq(key, k) ? v : defaultValue;
}
@Override
public void forEach(BiConsumer<? super K, ? super V> action) {
action.accept(k, v);
}
@Override
public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) {
throw new UnsupportedOperationException();
}
@Override
public V putIfAbsent(K key, V value) {
throw new UnsupportedOperationException();
}
@Override
public boolean remove(Object key, Object value) {
throw new UnsupportedOperationException();
}
@Override
public boolean replace(K key, V oldValue, V newValue) {
throw new UnsupportedOperationException();
}
@Override
public V replace(K key, V value) {
throw new UnsupportedOperationException();
}
@Override
public V computeIfAbsent(K key,
Function<? super K, ? extends V> mappingFunction) {
throw new UnsupportedOperationException();
}
@Override
public V computeIfPresent(K key,
BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
throw new UnsupportedOperationException();
}
@Override
public V compute(K key,
BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
throw new UnsupportedOperationException();
}
@Override
public V merge(K key, V value,
BiFunction<? super V, ? super V, ? extends V> remappingFunction) {
throw new UnsupportedOperationException();
}
}
// Miscellaneous
/**
* Returns an immutable list consisting of <tt>n</tt> copies of the
* specified object. The newly allocated data object is tiny (it contains
* a single reference to the data object). This method is useful in
* combination with the <tt>List.addAll</tt> method to grow lists.
* The returned list is serializable.
*
* @param <T> the class of the object to copy and of the objects
* in the returned list.
* @param n the number of elements in the returned list.
* @param o the element to appear repeatedly in the returned list.
* @return an immutable list consisting of <tt>n</tt> copies of the
* specified object.
* @throws IllegalArgumentException if {@code n < 0}
* @see List#addAll(Collection)
* @see List#addAll(int, Collection)
*/
public static <T> List<T> nCopies(int n, T o) {
if (n < 0)
throw new IllegalArgumentException("List length = " n);
return new CopiesList<>(n, o);
}
/**
* @serial include
*/
private static class CopiesList<E>
extends AbstractList<E>
implements RandomAccess, Serializable
{
private static final long serialVersionUID = 2739099268398711800L;
final int n;
final E element;
CopiesList(int n, E e) {
assert n >= 0;
this.n = n;
element = e;
}
public int size() {
return n;
}
public boolean contains(Object obj) {
return n != 0 && eq(obj, element);
}
public int indexOf(Object o) {
return contains(o) ? 0 : -1;
}
public int lastIndexOf(Object o) {
return contains(o) ? n - 1 : -1;
}
public E get(int index) {
if (index < 0 || index >= n)
throw new IndexOutOfBoundsException("Index: " index
", Size: " n);
return element;
}
public Object[] toArray() {
final Object[] a = new Object[n];
if (element != null)
Arrays.fill(a, 0, n, element);
return a;
}
@SuppressWarnings("unchecked")
public <T> T[] toArray(T[] a) {
final int n = this.n;
if (a.length < n) {
a = (T[])java.lang.reflect.Array
.newInstance(a.getClass().getComponentType(), n);
if (element != null)
Arrays.fill(a, 0, n, element);
} else {
Arrays.fill(a, 0, n, element);
if (a.length > n)
a[n] = null;
}
return a;
}
public List<E> subList(int fromIndex, int toIndex) {
if (fromIndex < 0)
throw new IndexOutOfBoundsException("fromIndex = " fromIndex);
if (toIndex > n)
throw new IndexOutOfBoundsException("toIndex = " toIndex);
if (fromIndex > toIndex)
throw new IllegalArgumentException("fromIndex(" fromIndex
") > toIndex(" toIndex ")");
return new CopiesList<>(toIndex - fromIndex, element);
}
// Override default methods in Collection
@Override
public Stream<E> stream() {
return IntStream.range(0, n).mapToObj(i -> element);
}
@Override
public Stream<E> parallelStream() {
return IntStream.range(0, n).parallel().mapToObj(i -> element);
}
@Override
public Spliterator<E> spliterator() {
return stream().spliterator();
}
}
/**
* Returns a comparator that imposes the reverse of the <em>natural
* ordering</em> on a collection of objects that implement the
* {@code Comparable} interface. (The natural ordering is the ordering
* imposed by the objects' own {@code compareTo} method.) This enables a
* simple idiom for sorting (or maintaining) collections (or arrays) of
* objects that implement the {@code Comparable} interface in
* reverse-natural-order. For example, suppose {@code a} is an array of
* strings. Then: <pre>
* Arrays.sort(a, Collections.reverseOrder());
* </pre> sorts the array in reverse-lexicographic (alphabetical) order.<p>
*
* The returned comparator is serializable.
*
* @param <T> the class of the objects compared by the comparator
* @return A comparator that imposes the reverse of the <i>natural
* ordering</i> on a collection of objects that implement
* the <tt>Comparable</tt> interface.
* @see Comparable
*/
@SuppressWarnings("unchecked")
public static <T> Comparator<T> reverseOrder() {
return (Comparator<T>) ReverseComparator.REVERSE_ORDER;
}
/**
* @serial include
*/
private static class ReverseComparator
implements Comparator<Comparable<Object>>, Serializable {
private static final long serialVersionUID = 7207038068494060240L;
static final ReverseComparator REVERSE_ORDER
= new ReverseComparator();
public int compare(Comparable<Object> c1, Comparable<Object> c2) {
return c2.compareTo(c1);
}
private Object readResolve() { return Collections.reverseOrder(); }
@Override
public Comparator<Comparable<Object>> reversed() {
return Comparator.naturalOrder();
}
}
/**
* Returns a comparator that imposes the reverse ordering of the specified
* comparator. If the specified comparator is {@code null}, this method is
* equivalent to {@link #reverseOrder()} (in other words, it returns a
* comparator that imposes the reverse of the <em>natural ordering</em> on
* a collection of objects that implement the Comparable interface).
*
* <p>The returned comparator is serializable (assuming the specified
* comparator is also serializable or {@code null}).
*
* @param <T> the class of the objects compared by the comparator
* @param cmp a comparator who's ordering is to be reversed by the returned
* comparator or {@code null}
* @return A comparator that imposes the reverse ordering of the
* specified comparator.
* @since 1.5
*/
public static <T> Comparator<T> reverseOrder(Comparator<T> cmp) {
if (cmp == null)
return reverseOrder();
if (cmp instanceof ReverseComparator2)
return ((ReverseComparator2<T>)cmp).cmp;
return new ReverseComparator2<>(cmp);
}
/**
* @serial include
*/
private static class ReverseComparator2<T> implements Comparator<T>,
Serializable
{
private static final long serialVersionUID = 4374092139857L;
/**
* The comparator specified in the static factory. This will never
* be null, as the static factory returns a ReverseComparator
* instance if its argument is null.
*
* @serial
*/
final Comparator<T> cmp;
ReverseComparator2(Comparator<T> cmp) {
assert cmp != null;
this.cmp = cmp;
}
public int compare(T t1, T t2) {
return cmp.compare(t2, t1);
}
public boolean equals(Object o) {
return (o == this) ||
(o instanceof ReverseComparator2 &&
cmp.equals(((ReverseComparator2)o).cmp));
}
public int hashCode() {
return cmp.hashCode() ^ Integer.MIN_VALUE;
}
@Override
public Comparator<T> reversed() {
return cmp;
}
}
/**
* Returns an enumeration over the specified collection. This provides
* interoperability with legacy APIs that require an enumeration
* as input.
*
* @param <T> the class of the objects in the collection
* @param c the collection for which an enumeration is to be returned.
* @return an enumeration over the specified collection.
* @see Enumeration
*/
public static <T> Enumeration<T> enumeration(final Collection<T> c) {
return new Enumeration<T>() {
private final Iterator<T> i = c.iterator();
public boolean hasMoreElements() {
return i.hasNext();
}
public T nextElement() {
return i.next();
}
};
}
/**
* Returns an array list containing the elements returned by the
* specified enumeration in the order they are returned by the
* enumeration. This method provides interoperability between
* legacy APIs that return enumerations and new APIs that require
* collections.
*
* @param <T> the class of the objects returned by the enumeration
* @param e enumeration providing elements for the returned
* array list
* @return an array list containing the elements returned
* by the specified enumeration.
* @since 1.4
* @see Enumeration
* @see ArrayList
*/
public static <T> ArrayList<T> list(Enumeration<T> e) {
ArrayList<T> l = new ArrayList<>();
while (e.hasMoreElements())
l.add(e.nextElement());
return l;
}
/**
* Returns true if the specified arguments are equal, or both null.
*
* NB: Do not replace with Object.equals until JDK-8015417 is resolved.
*/
static boolean eq(Object o1, Object o2) {
return o1==null ? o2==null : o1.equals(o2);
}
/**
* Returns the number of elements in the specified collection equal to the
* specified object. More formally, returns the number of elements
* <tt>e</tt> in the collection such that
* <tt>(o == null ? e == null : o.equals(e))</tt>.
*
* @param c the collection in which to determine the frequency
* of <tt>o</tt>
* @param o the object whose frequency is to be determined
* @return the number of elements in {@code c} equal to {@code o}
* @throws NullPointerException if <tt>c</tt> is null
* @since 1.5
*/
public static int frequency(Collection<?> c, Object o) {
int result = 0;
if (o == null) {
for (Object e : c)
if (e == null)
result ;
} else {
for (Object e : c)
if (o.equals(e))
result ;
}
return result;
}
/**
* Returns {@code true} if the two specified collections have no
* elements in common.
*
* <p>Care must be exercised if this method is used on collections that
* do not comply with the general contract for {@code Collection}.
* Implementations may elect to iterate over either collection and test
* for containment in the other collection (or to perform any equivalent
* computation). If either collection uses a nonstandard equality test
* (as does a {@link SortedSet} whose ordering is not <em>compatible with
* equals</em>, or the key set of an {@link IdentityHashMap}), both
* collections must use the same nonstandard equality test, or the
* result of this method is undefined.
*
* <p>Care must also be exercised when using collections that have
* restrictions on the elements that they may contain. Collection
* implementations are allowed to throw exceptions for any operation
* involving elements they deem ineligible. For absolute safety the
* specified collections should contain only elements which are
* eligible elements for both collections.
*
* <p>Note that it is permissible to pass the same collection in both
* parameters, in which case the method will return {@code true} if and
* only if the collection is empty.
*
* @param c1 a collection
* @param c2 a collection
* @return {@code true} if the two specified collections have no
* elements in common.
* @throws NullPointerException if either collection is {@code null}.
* @throws NullPointerException if one collection contains a {@code null}
* element and {@code null} is not an eligible element for the other collection.
* (<a href="Collection.html#optional-restrictions">optional</a>)
* @throws ClassCastException if one collection contains an element that is
* of a type which is ineligible for the other collection.
* (<a href="Collection.html#optional-restrictions">optional</a>)
* @since 1.5
*/
public static boolean disjoint(Collection<?> c1, Collection<?> c2) {
// The collection to be used for contains(). Preference is given to
// the collection who's contains() has lower O() complexity.
Collection<?> contains = c2;
// The collection to be iterated. If the collections' contains() impl
// are of different O() complexity, the collection with slower
// contains() will be used for iteration. For collections who's
// contains() are of the same complexity then best performance is
// achieved by iterating the smaller collection.
Collection<?> iterate = c1;
// Performance optimization cases. The heuristics:
// 1. Generally iterate over c1.
// 2. If c1 is a Set then iterate over c2.
// 3. If either collection is empty then result is always true.
// 4. Iterate over the smaller Collection.
if (c1 instanceof Set) {
// Use c1 for contains as a Set's contains() is expected to perform
// better than O(N/2)
iterate = c2;
contains = c1;
} else if (!(c2 instanceof Set)) {
// Both are mere Collections. Iterate over smaller collection.
// Example: If c1 contains 3 elements and c2 contains 50 elements and
// assuming contains() requires ceiling(N/2) comparisons then
// checking for all c1 elements in c2 would require 75 comparisons
// (3 * ceiling(50/2)) vs. checking all c2 elements in c1 requiring
// 100 comparisons (50 * ceiling(3/2)).
int c1size = c1.size();
int c2size = c2.size();
if (c1size == 0 || c2size == 0) {
// At least one collection is empty. Nothing will match.
return true;
}
if (c1size > c2size) {
iterate = c2;
contains = c1;
}
}
for (Object e : iterate) {
if (contains.contains(e)) {
// Found a common element. Collections are not disjoint.
return false;
}
}
// No common elements were found.
return true;
}
/**
* Adds all of the specified elements to the specified collection.
* Elements to be added may be specified individually or as an array.
* The behavior of this convenience method is identical to that of
* <tt>c.addAll(Arrays.asList(elements))</tt>, but this method is likely
* to run significantly faster under most implementations.
*
* <p>When elements are specified individually, this method provides a
* convenient way to add a few elements to an existing collection:
* <pre>
* Collections.addAll(flavors, "Peaches 'n Plutonium", "Rocky Racoon");
* </pre>
*
* @param <T> the class of the elements to add and of the collection
* @param c the collection into which <tt>elements</tt> are to be inserted
* @param elements the elements to insert into <tt>c</tt>
* @return <tt>true</tt> if the collection changed as a result of the call
* @throws UnsupportedOperationException if <tt>c</tt> does not support
* the <tt>add</tt> operation
* @throws NullPointerException if <tt>elements</tt> contains one or more
* null values and <tt>c</tt> does not permit null elements, or
* if <tt>c</tt> or <tt>elements</tt> are <tt>null</tt>
* @throws IllegalArgumentException if some property of a value in
* <tt>elements</tt> prevents it from being added to <tt>c</tt>
* @see Collection#addAll(Collection)
* @since 1.5
*/
@SafeVarargs
public static <T> boolean addAll(Collection<? super T> c, T... elements) {
boolean result = false;
for (T element : elements)
result |= c.add(element);
return result;
}
/**
* Returns a set backed by the specified map. The resulting set displays
* the same ordering, concurrency, and performance characteristics as the
* backing map. In essence, this factory method provides a {@link Set}
* implementation corresponding to any {@link Map} implementation. There
* is no need to use this method on a {@link Map} implementation that
* already has a corresponding {@link Set} implementation (such as {@link
* HashMap} or {@link TreeMap}).
*
* <p>Each method invocation on the set returned by this method results in
* exactly one method invocation on the backing map or its <tt>keySet</tt>
* view, with one exception. The <tt>addAll</tt> method is implemented
* as a sequence of <tt>put</tt> invocations on the backing map.
*
* <p>The specified map must be empty at the time this method is invoked,
* and should not be accessed directly after this method returns. These
* conditions are ensured if the map is created empty, passed directly
* to this method, and no reference to the map is retained, as illustrated
* in the following code fragment:
* <pre>
* Set<Object> weakHashSet = Collections.newSetFromMap(
* new WeakHashMap<Object, Boolean>());
* </pre>
*
* @param <E> the class of the map keys and of the objects in the
* returned set
* @param map the backing map
* @return the set backed by the map
* @throws IllegalArgumentException if <tt>map</tt> is not empty
* @since 1.6
*/
public static <E> Set<E> newSetFromMap(Map<E, Boolean> map) {
return new SetFromMap<>(map);
}
/**
* @serial include
*/
private static class SetFromMap<E> extends AbstractSet<E>
implements Set<E>, Serializable
{
private final Map<E, Boolean> m; // The backing map
private transient Set<E> s; // Its keySet
SetFromMap(Map<E, Boolean> map) {
if (!map.isEmpty())
throw new IllegalArgumentException("Map is non-empty");
m = map;
s = map.keySet();
}
public void clear() { m.clear(); }
public int size() { return m.size(); }
public boolean isEmpty() { return m.isEmpty(); }
public boolean contains(Object o) { return m.containsKey(o); }
public boolean remove(Object o) { return m.remove(o) != null; }
public boolean add(E e) { return m.put(e, Boolean.TRUE) == null; }
public Iterator<E> iterator() { return s.iterator(); }
public Object[] toArray() { return s.toArray(); }
public <T> T[] toArray(T[] a) { return s.toArray(a); }
public String toString() { return s.toString(); }
public int hashCode() { return s.hashCode(); }
public boolean equals(Object o) { return o == this || s.equals(o); }
public boolean containsAll(Collection<?> c) {return s.containsAll(c);}
public boolean removeAll(Collection<?> c) {return s.removeAll(c);}
public boolean retainAll(Collection<?> c) {return s.retainAll(c);}
// addAll is the only inherited implementation
// Override default methods in Collection
@Override
public void forEach(Consumer<? super E> action) {
s.forEach(action);
}
@Override
public boolean removeIf(Predicate<? super E> filter) {
return s.removeIf(filter);
}
@Override
public Spliterator<E> spliterator() {return s.spliterator();}
@Override
public Stream<E> stream() {return s.stream();}
@Override
public Stream<E> parallelStream() {return s.parallelStream();}
private static final long serialVersionUID = 2454657854757543876L;
private void readObject(java.io.ObjectInputStream stream)
throws IOException, ClassNotFoundException
{
stream.defaultReadObject();
s = m.keySet();
}
}
/**
* Returns a view of a {@link Deque} as a Last-in-first-out (Lifo)
* {@link Queue}. Method <tt>add</tt> is mapped to <tt>push</tt>,
* <tt>remove</tt> is mapped to <tt>pop</tt> and so on. This
* view can be useful when you would like to use a method
* requiring a <tt>Queue</tt> but you need Lifo ordering.
*
* <p>Each method invocation on the queue returned by this method
* results in exactly one method invocation on the backing deque, with
* one exception. The {@link Queue#addAll addAll} method is
* implemented as a sequence of {@link Deque#addFirst addFirst}
* invocations on the backing deque.
*
* @param <T> the class of the objects in the deque
* @param deque the deque
* @return the queue
* @since 1.6
*/
public static <T> Queue<T> asLifoQueue(Deque<T> deque) {
return new AsLIFOQueue<>(deque);
}
/**
* @serial include
*/
static class AsLIFOQueue<E> extends AbstractQueue<E>
implements Queue<E>, Serializable {
private static final long serialVersionUID = 1802017725587941708L;
private final Deque<E> q;
AsLIFOQueue(Deque<E> q) { this.q = q; }
public boolean add(E e) { q.addFirst(e); return true; }
public boolean offer(E e) { return q.offerFirst(e); }
public E poll() { return q.pollFirst(); }
public E remove() { return q.removeFirst(); }
public E peek() { return q.peekFirst(); }
public E element() { return q.getFirst(); }
public void clear() { q.clear(); }
public int size() { return q.size(); }
public boolean isEmpty() { return q.isEmpty(); }
public boolean contains(Object o) { return q.contains(o); }
public boolean remove(Object o) { return q.remove(o); }
public Iterator<E> iterator() { return q.iterator(); }
public Object[] toArray() { return q.toArray(); }
public <T> T[] toArray(T[] a) { return q.toArray(a); }
public String toString() { return q.toString(); }
public boolean containsAll(Collection<?> c) {return q.containsAll(c);}
public boolean removeAll(Collection<?> c) {return q.removeAll(c);}
public boolean retainAll(Collection<?> c) {return q.retainAll(c);}
// We use inherited addAll; forwarding addAll would be wrong
// Override default methods in Collection
@Override
public void forEach(Consumer<? super E> action) {q.forEach(action);}
@Override
public boolean removeIf(Predicate<? super E> filter) {
return q.removeIf(filter);
}
@Override
public Spliterator<E> spliterator() {return q.spliterator();}
@Override
public Stream<E> stream() {return q.stream();}
@Override
public Stream<E> parallelStream() {return q.parallelStream();}
}
}
