For list java example

3 Examples to Loop over a List in Java — ArrayList, LinkedList or Vector

There are multiple ways to traverse or loop through a List in Java e.g. by using an Iterator, by using an enhanced for loop of Java 5, and not the forEach() method of Java 8. Given a List is an index-based collection if you know the index you can retrieve an object from a List and because of this, you can also use a traditional for loop which keeps count for iterating a List . Now the question is whether should you use the Iterator or enhanced for loop, or the forEach() method of Java 8 for looping over List in Java .

Well, it depends on what you are doing with the object, if you need to r emove some objects from List then iterating using Iterator is the best choice to a void ConcurrentModificationException, but if you are not removing any element and just doing some operation with each element than enhanced for loop is much cleaner ways to do that.

The main advantage of using enhanced for loop over Iterator is that you don’t need to check for the next element like you need to in the case of Iterator , Java 5 advanced for loop keeps track of size. Also, the code is very clean with no boilerplate.

But, like everything else in the world, you won’t get all benefits, you do have some limitations while loop through a List using enhanced for loop, as shown here.

With the enhanced for loop, you can not modify selective objects as you don’t have an index with you. If you want to selective modify only certain objects then your best bet is to use the traditional for loop which keeps track of indexes.

The third choice is very straightforward, if you are running on Java SE 8 version then there is no reason for not using the forEach() method for looping through a List in Java. It’s lazy and allows you to perform some filtering operation on the stream before fetching an element from the list.

The laziness comes from the Stream class itself. You can check out The Complete Java Masterclass to learn more about the performance benefits provided by lambda expression and stream in Java 8.

3 Examples of looping through a List in Java

Here is a sample Java program that demonstrates How to loop through a List in Java in three different ways, Iterator , for-each loop, and traditional for loop. This technique can be used to loop through Array List or any other index-based List implementation like Vector.

The other two methods like Iterator and enhanced for loop can be used along with any Collection class like HashSet , TreeSet , LinkedHashSet, etc. They are actually the standard way to iterate through the collection in Java.

The traditional for loop approach is only possible and efficient because of the index-based nature of the List interface, but if you use this with a linked list then you will get worse performance because in LinkedList accessing an element with an index is O(n) operation rather than O(1) operation. This is also the fundamental difference between an ArrayList and LinkedList in Java.

The new method of iterating over a list using the forEach() method is only available in Java SE 8 and I recommend you to read this article to learn how to loop through a list using the forEach() method in Java 8 before you start using them.

Btw, Java SE 8 is full of exciting and more powerful features and it’s essential for a Java developer to learn those features, given it’s the most popular Java version. If you are interested, you should follow a good Java 8 course like What’s New in Java 8 on Pluralsight to learn quickly.

Alternatively, you can always choose the one from this list of good Java 8 books, earlier published by me.

How to loop over a List in Java

Here is our complete Java program to show you all three ways to loop over a list in Java. You can use these methods to loop over any List like ArrayList, LinkedList, or even Vector in Java.

import java.util.Arrays ;
import java.util.Iterator ;
import java.util.List ;
/**
*
* Java program to demonstrate different ways to loop,
* iterate or traverse List in Java.

* a List in Java.
*
* @author Javin Paul
*/
public class ListLoopExample

public static void main ( String args [])

//First example to iterate List in Java using Iterator
List < String > languages = Arrays. asList ( «Java» ,
«C++» , «Scala» , «Groovy» ) ;

//Getting Iterator from List in Java
Iterator < String > iterator = languages. iterator () ;
System. out . println ( «Iterating List in Java
using Iterator » ) ;

//Iterating through all elements of List
while ( iterator. hasNext ()) <
System. out . printf ( «Current element in List
is %s %n» , iterator. next ()) ;
>

//Second example of Iterating over List in Java
// using a foreach loop
System. out . println ( «Looping List in Java using a
foreach loop» ) ;
for ( String city : languages ) <
System. out . println ( «List Element: » + city ) ;
>

//Third example of Looping List using traditional for loop
for ( int i = 0 ; i < languages. size () ; i++ )<
System. out . printf ( «programming language #%d in
List is : %s %n» , i, languages. get ( i ) ) ;
>

Output:
Iterating List in Java using Iterator
The current element in List is London
The current element in List is Tokyo
The current element in List is NewYork
The current element in List in Mumbai
Looping List in Java using a foreach loop
List Element: London
List Element: Tokyo
List Element: NewYork
List Element: Mumbai
City # 0 in List is: London
City # 1 in List is: Tokyo
City # 2 in List is: NewYork
City # 3 in List is: Mumbai

That’s all on How to iterate or loop over a List in Java. In this Java tutorial, we have seen an example of all three ways of looping List in Java. the first example demonstrates the use of Iterator with List , the second use for loop for looping over List, and the third example uses traditional old for a loop. All this technique can be applied to any index-based List implementation including ArrayList and Vector in Java .

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How to iterate through Java List? Seven (7) ways to Iterate Through Loop in Java

How to iterate through Java List? This tutorial demonstrates the use of ArrayList, Iterator and a List.

There are 7 ways you can iterate through List.

1. Simple For loop
2. Enhanced For loop
3. Iterator
4. ListIterator
5. While loop
6. Iterable.forEach() util
7. Stream.forEach() util

Java Example:

You need JDK 13 to run below program as point-5 above uses stream() util.

void java.util.stream.Stream.forEach (Consumer action) p erforms an action for each element of this stream.

package crunchify.com.tutorials; import java.util.*; /** * @author Crunchify.com * How to iterate through Java List? Seven (7) ways to Iterate Through Loop in Java. * 1. Simple For loop * 2. Enhanced For loop * 3. Iterator * 4. ListIterator * 5. While loop * 6. Iterable.forEach() util * 7. Stream.forEach() util */ public class CrunchifyIterateThroughList < public static void main(String[] argv) < // create list ListcrunchifyList = new ArrayList(); // add 4 different values to list crunchifyList.add("Facebook"); crunchifyList.add("Paypal"); crunchifyList.add("Google"); crunchifyList.add("Yahoo"); // Other way to define list is - we will not use this list :) List crunchifyListNew = Arrays.asList("Facebook", "Paypal", "Google", "Yahoo"); // Simple For loop System.out.println("==============> 1. Simple For loop Example."); for (int i = 0; i < crunchifyList.size(); i++) < System.out.println(crunchifyList.get(i)); >// New Enhanced For loop System.out.println("\n==============> 2. New Enhanced For loop Example.."); for (String temp : crunchifyList) < System.out.println(temp); >// Iterator - Returns an iterator over the elements in this list in proper sequence. System.out.println("\n==============> 3. Iterator Example. "); Iterator crunchifyIterator = crunchifyList.iterator(); while (crunchifyIterator.hasNext()) < System.out.println(crunchifyIterator.next()); >// ListIterator - traverse a list of elements in either forward or backward order // An iterator for lists that allows the programmer to traverse the list in either direction, modify the list during iteration, // and obtain the iterator's current position in the list. System.out.println("\n==============> 4. ListIterator Example. "); ListIterator crunchifyListIterator = crunchifyList.listIterator(); while (crunchifyListIterator.hasNext()) < System.out.println(crunchifyListIterator.next()); >// while loop System.out.println("\n==============> 5. While Loop Example. "); int i = 0; while (i < crunchifyList.size()) < System.out.println(crunchifyList.get(i)); i++; >// Iterable.forEach() util: Returns a sequential Stream with this collection as its source System.out.println("\n==============> 6. Iterable.forEach() Example. "); crunchifyList.forEach((temp) -> < System.out.println(temp); >); // collection Stream.forEach() util: Returns a sequential Stream with this collection as its source System.out.println("\n==============> 7. Stream.forEach() Example. "); crunchifyList.stream().forEach((crunchifyTemp) -> System.out.println(crunchifyTemp)); > >

Output:

==============> 1. Simple For loop Example. Facebook Paypal Google Yahoo ==============> 2. New Enhanced For loop Example.. Facebook Paypal Google Yahoo ==============> 3. Iterator Example. Facebook Paypal Google Yahoo ==============> 4. ListIterator Example. Facebook Paypal Google Yahoo ==============> 5. While Loop Example. Facebook Paypal Google Yahoo ==============> 6. Iterable.forEach() Example. Facebook Paypal Google Yahoo ==============> 7. Stream.forEach() Example. Facebook Paypal Google Yahoo Process finished with exit code 0

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