LinkedHashMap

Class Overview

LinkedHashMap is a variant of HashMap. Its entries are kept in a doubly-linked list. The iteration order is, by default, the order in which keys were inserted. Reinserting an already existing key doesn't change the order. A key is existing if a call to containsKey would return true.

If the three argument constructor is used, and order is specified as true, the iteration will be in the order that entries were accessed. The access order gets affected by put(), get(), putAll() operations, but not by operations on the collection views.

Null elements are allowed, and all the optional map operations are supported.

Note: The implementation of LinkedHashMap is not synchronized. If one thread of several threads accessing an instance modifies the map structurally, access to the map needs to be synchronized. For insertion-ordered instances a structural modification is an operation that removes or adds an entry. Access-ordered instances also are structurally modified by put(), get() and putAll() since these methods change the order of the entries. Changes in the value of an entry are not structural changes.

The Iterator that can be created by calling the iterator method throws a ConcurrentModificationException if the map is structurally changed while an iterator is used to iterate over the elements. Only the remove method that is provided by the iterator allows for removal of elements during iteration. It is not possible to guarantee that this mechanism works in all cases of unsynchronized concurrent modification. It should only be used for debugging purposes.

Summary

[Expand] Inherited Methods
From class java.util.HashMap void clear() Removes all mappings from this hash map, leaving it empty. Object clone() Returns a shallow copy of this map. boolean containsKey(Object key) Returns whether this map contains the specified key. boolean containsValue(Object value) Returns whether this map contains the specified value. Set<Entry<K, V>> entrySet() Returns a set containing all of the mappings in this map. V get(Object key) Returns the value of the mapping with the specified key. boolean isEmpty() Returns whether this map is empty. Set<K> keySet() Returns a set of the keys contained in this map. V put(K key, V value) Maps the specified key to the specified value. void putAll(Map<? extends K, ? extends V> map) Copies all the mappings in the specified map to this map. V remove(Object key) Removes the mapping with the specified key from this map. int size() Returns the number of elements in this map. Collection<V> values() Returns a collection of the values contained in this map.
From class java.util.AbstractMap void clear() Removes all elements from this map, leaving it empty. Object clone() Returns a new instance of the same class as this instance, whose slots have been filled in with the values of the slots of this instance. boolean containsKey(Object key) Returns whether this map contains the specified key. boolean containsValue(Object value) Returns whether this map contains the specified value. abstract Set<Entry<K, V>> entrySet() Returns a set containing all of the mappings in this map. boolean equals(Object object) Compares the specified object to this instance, and returns true if the specified object is a map and both maps contain the same mappings. V get(Object key) Returns the value of the mapping with the specified key. int hashCode() Returns the hash code for this object. boolean isEmpty() Returns whether this map is empty. Set<K> keySet() Returns a set of the keys contained in this map. V put(K key, V value) Maps the specified key to the specified value. void putAll(Map<? extends K, ? extends V> map) Copies every mapping in the specified map to this map. V remove(Object key) Removes a mapping with the specified key from this Map. int size() Returns the number of elements in this map. String toString() Returns the string representation of this map. Collection<V> values() Returns a collection of the values contained in this map.
From class java.lang.Object Object clone() Creates and returns a copy of this Object. boolean equals(Object o) Compares this instance with the specified object and indicates if they are equal. void finalize() Is called before the object's memory is being reclaimed by the VM. final Class<? extends Object> getClass() Returns the unique instance of Class which represents this object's class. int hashCode() Returns an integer hash code for this object. final void notify() Causes a thread which is waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up. final void notifyAll() Causes all threads which are waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up. String toString() Returns a string containing a concise, human-readable description of this object. final void wait(long millis, int nanos) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires. final void wait(long millis) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires. final void wait() Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object.
From interface java.util.Map abstract void clear() Removes all elements from this Map, leaving it empty. abstract boolean containsKey(Object key) Returns whether this Map contains the specified key. abstract boolean containsValue(Object value) Returns whether this Map contains the specified value. abstract Set<Entry<K, V>> entrySet() Returns a Set containing all of the mappings in this Map. abstract boolean equals(Object object) Compares the argument to the receiver, and returns true if the specified object is a Map and both Maps contain the same mappings. abstract V get(Object key) Returns the value of the mapping with the specified key. abstract int hashCode() Returns an integer hash code for the receiver. abstract boolean isEmpty() Returns whether this map is empty. abstract Set<K> keySet() Returns a set of the keys contained in this Map. abstract V put(K key, V value) Maps the specified key to the specified value. abstract void putAll(Map<? extends K, ? extends V> map) Copies every mapping in the specified Map to this Map. abstract V remove(Object key) Removes a mapping with the specified key from this Map. abstract int size() Returns the number of mappings in this Map. abstract Collection<V> values() Returns a Collection of the values contained in this Map.