Java HashMap Tutorial with Example program

By candid | Posted : Dec 11, 2015 | Updated : Dec 11, 2015

Class HashMap

Type Parameters:

K - the type of keys maintained by this map

V - the type of mapped values

All Implemented Interfaces:

Serializable, Cloneable, Map

Direct Known Subclasses:

LinkedHashMap, PrinterStateReasons

public class HashMap
extends AbstractMap
implements Map, Cloneable, Serializable
{

   //
}

Since:

1.2

See Also:

Object.hashCode(), Collection, Map, TreeMap, Hashtable, Serialized Form

Nested classes/interfaces inherited from class java.util.AbstractMap

AbstractMap.SimpleEntry, AbstractMap.SimpleImmutableEntry

Constructor summary

HashMap()

Constructs an empty HashMap with the default initial capacity (16) and the default load factor (0.75).

HashMap(int initialCapacity)

Constructs an empty HashMap with the specified initial capacity and the default load factor (0.75).

HashMap(int initialCapacity, float loadFactor)

Constructs an empty HashMap with the specified initial capacity and load factor.

HashMap(Map m)

Constructs a new HashMap with the same mappings as the specified Map.

Methods Summary

void clear()

Removes all of the mappings from this map.

Object clone()

Returns a shallow copy of this HashMap instance: the keys and values themselves are not cloned.

boolean containsKey(Object key)

Returns true if this map contains a mapping for the specified key.

boolean containsValue(Object value)

Returns true if this map maps one or more keys to the specified value.

Set entrySet()

Returns a Set view of the mappings contained in this map.

V get(Object key)

Returns the value to which the specified key is mapped, or null if this map contains no mapping for the key.

boolean isEmpty()

Returns true if this map contains no key-value mappings.

Set keySet()

Returns a Set view of the keys contained in this map.

V put(K key, V value)

Associates the specified value with the specified key in this map.

void putAll(Map m)

Copies all of the mappings from the specified map to this map.

V remove(Object key)

Removes the mapping for the specified key from this map if present.

int size()

Returns the number of key-value mappings in this map.

Collection values()

Returns a Collection view of the values contained in this map.

Methods inherited from class java.lang.Object

finalize, getClass, notify, notifyAll, wait, wait, wait,equals, hashCode, toString

Java HashMap Tutorial with Example program

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