How to Loop or Iterate an Arraylist in Java

There are many ways to loop or iterate an ArrayList in Java. We can use the simple for loop, for-each loop (advanced for loop) available from Java 5 onwards, iterator or ListIterator (though not a preferred way if we are just sequentially looping through the elements of a list) and from Java 8 using Java 8 forEach statement that works with stream.

So the options available to loop through an ArrayList in Java are-

• for loop
• for-each loop
• iterator
• ListIterator
• Java 8 forEach loop

Java Example code to traverse an ArrayList

Let's see a program that will use all these ways to iterate an ArrayList in Java.

public class LoopListDemo {
  public static void main(String[] args) {
    List<String> cityList = new ArrayList<>();
    cityList.add("Delhi");
    cityList.add("Mumbai");
    cityList.add("Bangalore");
    cityList.add("Chennai");
    cityList.add("Kolkata");
    
    // Using for loop with size to iterate ArrayList
    System.out.println("With simple for loop");
    for(int i = 0; i < cityList.size(); i++){
      System.out.println("City Name - " + cityList.get(i));
    }
    
    // Using for-each loop to iterate ArrayList 
    System.out.println("With for-each loop - Java 5");
    for(String name : cityList){
      System.out.println("City Name - " + name);
    }
    
    // Using Iterator to iterate ArrayList
    System.out.println("With iterator - Java 5");
    Iterator<String> itr = cityList.iterator();
    while(itr.hasNext()){
      System.out.println("City Name - " + itr.next());
    }
    
    // Using List Iterator - though not needed if doing sequential looping
    System.out.println("With List iterator - Java 5");
    ListIterator<String> ltr = cityList.listIterator();
    while(ltr.hasNext()){        
      System.out.println("City Name - " + ltr.next());
    }
    
    //Using Java 8 iterable.forEach to iterate ArrayList
    System.out.println("With for-each loop - Java 8");
    
    cityList.forEach((a)->System.out.println("City Name - " + a));
    
    //Using Java 8 iterable.forEach loop with method reference
    cityList.forEach(System.out::println);
  }
}

Output (curtailed)

With simple for loop
City Name - Delhi
City Name - Mumbai
City Name - Bangalore
City Name - Chennai
City Name - Kolkata
With for-each loop - Java 5
City Name - Delhi
City Name - Mumbai
City Name - Bangalore
City Name - Chennai
City Name - Kolkata
With iterator - Java 5
City Name - Delhi
City Name - Mumbai
City Name - Bangalore
City Name - Chennai
City Name - Kolkata

In my opinion for-each loop is best way to iterate a list if you just need to traverse sequentially through a list.

With Java 8 and multi-core environment you can also use Java 8 forEach statement to take advantage of parallel computing using parallel stream. In that case you need to write it like-

cityList.parallelStream().forEach((a)->System.out.println("City Name - " + a));

That's all for this topic How to Loop or Iterate an Arraylist in Java. If you have any doubt or any suggestions to make please drop a comment. Thanks!

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