Wednesday, 30 November 2016

Program to demonstrate "HashMap" class in Java's Collection Framework

The Map interface maps unique keys to values. A key is an object that you use to retrieve a value at a later date. Given a key and a value, you can store the value in a Map object. After the value is stored, you can retrieve it by using its key. It stores value in pairs i.e key and value we can store data using put( ) method and fetch specific data using get( ) method we can print all data using entrySet( ) method. It has following methods:
  1. void clear( ) : Removes all key/value pairs from the invoking map.
  2. boolean containsKey(Object k) : Returns true if the invoking map contains k as a key. Otherwise, returns false.
  3. boolean containsValue(Object v) : Returns true if the map contains v as a value. Otherwise, returns false.
  4. Set entrySet( ) : Returns a Set that contains the entries in the map.
  5. boolean equals(Object obj) : Returns true if obj is a Map and contains the same entries. Otherwise, returns false.
  6. Object get(Object k) : Returns the value associated with the key k.
  7. Object put(Object k, Object v) : Puts an entry in the invoking map, overwriting any previous value associated with the key.
  8. Object remove(Object k) : Removes the entry whose key equals k.
  9. int size( ) : Returns the number of key/value pairs in the map.
  10. Collection values( ) : Returns a collection containing the values in the map.

PROGRAM
import java.util.HashMap;
import java.util.Map;

class MapDemo {

 public static void main(String[] args) {
  
  Map<String,String> q = new HashMap<String,String>();
  q.put("India","Delhi");
  q.put("Srilanka","Columbo");
  q.put("WestIndies","Jamayca");
  q.put("Australia","Sydney");
  
  for(Map.Entry<String,String> r :q.entrySet())
  {
   System.out.println(r.getKey() + "  " + r.getValue());
  }

  System.out.println("Get Value For Srilanka " + q.get("Srilanka"));
 }
}
OUTPUT
C:\>javac MapDemo.java
C:\>java MapDemo
Srilanka  Columbo
WestIndies  Jamayca
Australia  Sydney
India  Delhi
Get Value For Srilanka Columbo

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