Best Way to Iterate Any Map in java

Best Way to Iterate Any Map in java

Iterating over Map in java there are basically 4 different ways in this article we will look each and every one by one with example. Also we will use Java 8 forEach() method for iterating all the Map interface child class.

1] Iterating using enhanced for loop Example

This is basic and most used technique to iterate the any map implementations in java.

package com.vr.cls;

import java.util.HashMap;

import java.util.Map;

public class DifferentIteratingMapDemo {

     public static void main(String[] args) {

          

           Map map = new HashMap();

          

           map.put(20, "tiger");

           map.put(40, "lion");

           map.put(30, "parrot");

           map.put(70, "cow");

           map.put(50, "deer");

          

           for(Map.Entry entry : map.entrySet())

           {

                System.out.println("Key : "+entry.getKey() +" "+

                                        "value : "+entry.getValue());

           }

     }

}

Output

Key : 50 value : deer

Key : 20 value : tiger

Key : 70 value : cow

Key : 40 value : lion

Key : 30 value : parrot

2] Iterating using Iterator interface over Map.Entry

This is also basic and most used technique to iterate using Iterator interface over the Map.Entry, using this method benefits is to we can remove the element while iterating.

package com.vr.cls;

import java.util.HashMap;

import java.util.Iterator;

import java.util.Map;

import java.util.Map.Entry;

public class DifferentIteratingMapDemo {

     public static void main(String[] args) {

          

           Map map = new HashMap ();

          

           map.put(20, "tiger");

           map.put(40, "lion");

           map.put(30, "parrot");

           map.put(70, "cow");

           map.put(50, "deer");

          

            IteratoritrEntry =  map.entrySet().iterator();

           while (itrEntry.hasNext())

           {

                Entry entry = itrEntry.next();

               

                System.out.println("Key : "+entry.getKey() +" "+

                                        "value : "+entry.getValue());

           }

     }

}

3] Iterating using keySet () and values () method

This is very easy and simple method of iterating the element using keySet() and values() we can iterate the map for any particular requirement.

package com.vr.cls;

import java.util.HashMap;

import java.util.Map;

public class DifferentIteratingMapDemo {

     public static void main(String[] args) {

          

           Map map = new HashMap();

          

           map.put(20, "tiger");

           map.put(40, "lion");

           map.put(30, "parrot");

           map.put(70, "cow");

           map.put(50, "deer");

          

            for(Integer key : map.keySet()){

                 System.out.println(key);

            }

            

            for(String values : map.values()){

                 System.out.println(values);

            }

     }

}

Output

50

20

70

40

30

deer

tiger

cow

lion

parrot

4] Iterating using java 8 forEach () method

Using Java 8, you can iterate a map using Map.forEach() method using lambda expression.        

package com.vr.cls;

import java.util.HashMap;

import java.util.Map;

public class DifferentIteratingMapDemo {

     public static void main(String[] args) {

          

           Map map = new HashMap();

          

           map.put(20, "tiger");

           map.put(40, "lion");

           map.put(30, "parrot");

           map.put(70, "cow");

           map.put(50, "deer");

          

            

           map.forEach( (k, v) ->  System.out.println("key: "+k +"  value : "+v));

     }

}

Output

key: 50  value : deer

key: 20  value : tiger

key: 70  value : cow

key: 40  value : lion

key: 30  value : parrot