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 countryCapitalMap=new HashMap();
  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 countryCapitalMap=new HashMap();
  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:

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.