Java 8

forEach() method in Iterable interface

Whenever we need to traverse through a Collection, we need to create an Iterator whose whole purpose is to iterate over and then we have business logic in a loop for each of the elements in the Collection. We might get ConcurrentModificationException if iterator is not used properly.

Java 8 has introduced forEach method in java.lang.Iterable interface so that while writing code we focus on business logic only. forEach method takes java.util.function.Consumer object as argument, so it helps in having our business logic at a separate location that we can reuse. Let’s see forEach usage with simple example.

example

package com.leejo.forech;

import java.util.ArrayList;

import java.util.Iterator;

import java.util.List;

import java.util.function.Consumer;

import java.lang.Integer;

public class Java8ForEachExample {

public static void main(String[] args) {

//creating sample Collection

List<Integer> myList = new ArrayList<Integer>();

for(int i=0; i<10; i++) myList.add(i);

//traversing using Iterator

Iterator<Integer> it = myList.iterator();

while(it.hasNext()){

Integer i = it.next();

System.out.println("Iterator Value::"+i);

}

//traversing through forEach method of Iterable with anonymous class

myList.forEach(new Consumer<Integer>() {

public void accept(Integer t) {

System.out.println("forEach anonymous class Value::"+t);

}

});

//traversing with Consumer interface implementation

MyConsumer action = new MyConsumer();

myList.forEach(action);

}

}

//Consumer implementation that can be reused

class MyConsumer implements Consumer<Integer>{

public void accept(Integer t) {

System.out.println("Consumer impl Value::"+t);

}

}

---The number of lines might increase but forEach method helps in having the logic for iteration and business logic at separate place resulting in higher separation of concern and cleaner code.