Java - The Map Interface


The Map interface plots single keys to characters. A key is a value that you utilize to recover a value later.

  • Provided a key and an object, you can amass the cost in a Map object. After the worth is stored, you can regain it by utilizing its key
  • Many techniques throw a NoSuchElementException when no entries exist in the appealing map.
  • A ClassCastException is thrown when a value is irreconcilable with the objects in a map.
  • A NullPointerException is thrown if an effort is made to utilize a null entity and null is not tolerated in the map.
  • An UnsupportedOperationException is thrown when an effort is made to modify an unmodifiable map.
Sr.No.Method & Description

void clear( )

Removes all key/value pairs from the invoking map.


boolean containsKey(Object k)

Returns true if the invoking map contains k as a key. Otherwise, returns false.


boolean containsValue(Object v)

Returns true if the map contains v as a value. Otherwise, returns false.


Set entrySet( )

Returns a Set that contains the entries in the map. The set contains objects of type Map.Entry. This method provides a set-view of the invoking map.


boolean equals(Object obj)

Returns true if obj is a Map and contains the same entries. Otherwise, returns false.


Object get(Object k)

Returns the value associated with the key k.


int hashCode( )

Returns the hash code for the invoking map.


boolean isEmpty( )

Returns true if the invoking map is empty. Otherwise, returns false.


Set keySet( )

Returns a Set that contains the keys in the invoking map. This method provides a set-view of the keys in the invoking map.


Object put(Object k, Object v)

Puts an entry in the invoking map, overwriting any previous value associated with the key. The key and value are k and v, respectively. Returns null if the key did not already exist. Otherwise, the previous value linked to the key is returned.


void putAll(Map m)

Puts all the entries from m into this map.


Object remove(Object k)

Removes the entry whose key equals k.


int size( )

Returns the number of key/value pairs in the map.


Collection values( )

Returns a collection containing the values in the map. This method provides a collection-view of the values in the map.


Map has its implementation in various classes like HashMap. Following is an example to explain map functionality −

import java.util.*;
public class CollectionsDemo {

   public static void main(String[] args) {
      Map m1 = new HashMap(); 
      m1.put("Zara", "8");
      m1.put("Mahnaz", "31");
      m1.put("Ayan", "12");
      m1.put("Daisy", "14");

      System.out.println(" Map Elements");
      System.out.print("\t" + m1);

This will produce the following result −


Map Elements
	{Daisy = 14, Ayan = 12, Zara = 8, Mahnaz = 31}

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