Java 8 forEach examples

In this post, we will see improved way of iterating through map and list which are introduced in java 8.

Map:

Normal way of iterating HashMap before java 8:

package org.arpit.java2blog;

import java.util.HashMap;

public class HashMapIterationMap {

public static void main(String args[])

{

// HashMap with Country as key and capital as value

HashMap<String,String> countryCapitalMap=new HashMap<String,String>();

countryCapitalMap.put("India","Delhi");

countryCapitalMap.put("Japan","Tokyo");

countryCapitalMap.put("France","Paris");

countryCapitalMap.put("Russia","Moscow");

// Iterating Using keySet() and for each loop

System.out.println("Iterating Using keySet() and for each loop");

for (String countryKey:countryCapitalMap.keySet()) {

System.out.println("Country:"+ countryKey +" and Capital:"+countryCapitalMap.get(countryKey));

}

System.out.println("-----------------------------");

}

Improved way of iterating HashMap in java 8:

package org.arpit.java2blog;

import java.util.HashMap;

public class HashMapIterationMap {

public static void main(String args[])

{

// HashMap with Country as key and capital as value

HashMap<String,String> countryCapitalMap=new HashMap<String,String>();

countryCapitalMap.put("India","Delhi");

countryCapitalMap.put("Japan","Tokyo");

countryCapitalMap.put("France","Paris");

countryCapitalMap.put("Russia","Moscow");

// Iterating Using Java 8

System.out.println("Iterating Using Java 8");

System.out.println("-----------------------------");

countryCapitalMap.forEach((k,v)->System.out.println("Country:" + k + " Capital : " + v));

System.out.println("-----------------------------");

}

When you run above program, you will get below output:

Iterating Using Java 8
—————————–
Country:Japan Capital : Tokyo
Country:France Capital : Paris
Country:India Capital : Delhi
Country:Russia Capital : Moscow
—————————–

List:

Normal way of iterating list:

package org.arpit.java2blog;

import java.util.ArrayList;

public class IteratingArrayListMain {

public static void main(String[] args) {

ArrayList nameList=new ArrayList();//creating arraylist

nameList.add("Arpit");//adding object in arraylist

nameList.add("John");

nameList.add("Martin");

nameList.add("Adam");

// Iterating list using foreach loop

for(String name :nameList )

{

System.out.print(name+" ");

}

Iterating through list in java 8:

package org.arpit.java2blog;

import java.util.ArrayList;

public class IteratingArrayListMain {

public static void main(String[] args) {

ArrayList nameList=new ArrayList();//creating arraylist

nameList.add("Arpit");//adding object in arraylist

nameList.add("John");

nameList.add("Martin");

nameList.add("Adam");

// Iterating list using foreach method

nameList.forEach(n->System.out.print(n+" "));

}

forEach method internally use Consumer Object.You can read more about Java 8 Consumer interface.

Arpit John Martin Adam

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Java 8 forEach examples