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 Java > Collection > Maps > Map Manipulation

Map Manipulation 

The following example shows Map data manipulation. HashMap and Hashtable are two implementations of Map interface. Hashtable is synchronized where as HashMap is not. Map provides the following APIs,

public int size();
 - Returns the number of entries in the Map.
 
public boolean isEmpty();
 - Returns true if the Map contains more than one entry otherwise returns false. 
 
public V put(K paramK, V paramV);
 - Puts a key value pair as an entry in Map. 

public void putAll(Map<? extends K, ? extends V> paramMap);
 - Copies all Map entries from specified Map.
  
public V remove(Object paramObject);
 - Removes the specified entry from Map. 
 
public void clear();
 - Removes all entries from Map. 


File Name  :  
com/bethecoder/tutorials/utils/maps/ManipulateMap.java 
Author  :  Sudhakar KV
Email  :  kvenkatasudhakar@gmail.com
   
package com.bethecoder.tutorials.utils.maps;

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

public class ManipulateMap {

  /**
   @param args
   */
  public static void main(String[] args) {

    Map<Integer, String> numMap = new HashMap<Integer, String>();
    System.out.println("Is Map Empty ? : " + numMap.isEmpty());
    
    numMap.put(new Integer(1)"ONE");
    numMap.put(new Integer(2)"TWO");
    numMap.put(new Integer(3)"THREE");
    
    System.out.println("Map Size : " + numMap.size() " " + numMap);
    System.out.println("Is Map Empty ? : " + numMap.isEmpty());
    System.out.println();

    //Copy all map entries
    Map<Integer, String> numMap2 = new HashMap<Integer, String>();
    numMap2.put(new Integer(4)"FOUR");
    numMap2.put(new Integer(6)"SIX");
    
    numMap.putAll(numMap2);
    System.out.println("Map Size : " + numMap.size() " " + numMap);
    System.out.println("Is Map Empty ? : " + numMap.isEmpty());
    System.out.println();
    
    //Remove a particular key
    numMap.remove(new Integer(1));
    System.out.println("Map Size : " + numMap.size() " " + numMap);
    System.out.println("Is Map Empty ? : " + numMap.isEmpty());
    System.out.println();
    
    //Clear all map entries
    numMap.clear();
    System.out.println("Map Size : " + numMap.size() " " + numMap);
    System.out.println("Is Map Empty ? : " + numMap.isEmpty());
    
  }

}
   

It gives the following output,
Is Map Empty ? : true
Map Size : 3 {1=ONE, 2=TWO, 3=THREE}
Is Map Empty ? : false

Map Size : 5 {1=ONE, 2=TWO, 3=THREE, 4=FOUR, 6=SIX}
Is Map Empty ? : false

Map Size : 4 {2=TWO, 3=THREE, 4=FOUR, 6=SIX}
Is Map Empty ? : false

Map Size : 0 {}
Is Map Empty ? : true


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