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#.get method map java code

Example: Adding Elements to a Map in Java You will use the most commonly used HashMap to perform these operations. Some of the primary operations you can perform on the maps in Java are: The Map interface in Java can be used with the classes that implement it, to perform various operations. The flowchart diagram depicted below represents the hierarchy of Map interface in Java.ĭifferent Operations That Are Performed With Maps in Java TreeMap class implements the SortedMap interface that extends the Map interface.

void putAll(Map m) : copies all the elements of a map to the another specified map.The LinkedHashMap class extends HashMap that implements the Map interface.

Value remove(Object key) : removes the key-value pair for the specified key.

Collection values() : returns a collection of all values in the map.

int size() : returns the size of the map which is equal to the number of key-value pairs stored in the HashMap.

Object put(Key k, Value v) : Inserts key-value pair into the HashMap.

Set keySet() : returns the Set of the all keys stored in the HashMap.

boolean isEmpty() : checks whether the map is empty.

Object get(Object key) : returns the value for the specified key in the HashMap.

boolean containsValue(Object Value) : Similar to containsKey() method, it looks for the specified value instead of key.

boolean containsKey(Object key) : returns true or false based on whether the specified key is found in the map or not.

Object clone() : returns a shallow copy of the specified HashMap.

void clear() : removes all the key-value pairs from the HashMap.

List of methods in HashMap class and their short description. ('The key is :: ' + entry.getKey() + ', and value is :: ' + entry.getValue() )

Iterator entryIterator = map.entrySet().iterator() Įntry entry = entryIterator.next()

('The key is :: ' + key + ', and value is :: ' + value )

Iterator itr = map.keySet().iterator()

Please note that iterators of this class are fail-fast and if any structure modification is done after creation of iterator, it will throw ConcurrentModificationException.

HashMap map = new HashMap<>()

Public static void main(String args) throws CloneNotSupportedException Let’s quickly go through some examples to work with HashMap in Java. Then all elements are iterated in the linkedlist and correct value object is found by identifying the correct key using it’s equals() method. While retrieving the value by key, first index location is found using key’s hashcode. In case of collision, where multiple keys are mapped to single index location, a linked list of formed to store all such key-value pairs which should go in single array index location. This hash value is used to calculate the index in the array for storing Entry object. For each key-value to be stored in HashMap, a hash value is calculated using the key’s hash code.

Static class Entry implements Map.EntryĪll instances of Entry class are stored in an array declard as 'transient Entry table'.

The key-value pairs are stored as instance of inner class HashMap.Entry which has key and value mapping stored as attributes.

#.get method map java code

Each object in java has it’s hash code in such a way that two equal objects must produce the same hash code consistently. Hashing is a way to assigning a unique code for any variable/object after applying any formula/algorithm on its properties. HashMap implements Cloneable and Serializable interfaces.So primitives must be used with their corresponding wrapper classes. HashMap stores only object references.A value can be retrieved only using the associated key.Or you can use Collections.synchronizedMap(hashMap) to get the synchronized version of HashMap. You must explicitly synchronize concurrent modifications to the HashMap. It does not guarantee any specific order of the elements. HashMap allows multiple null values but only one null key.

Implements Map, Cloneable, SerializableĪs shown above, HashMap implements Map interface and extends AbstractMap class. Public class HashMap extends AbstractMap

Though a value 'V' can be mapped to multiple keys. It means we can insert a key ‘K’ only once in a map. Each key is mapped to a single value in the map. HashMap in Java in a collection class which implements Map interface.