Java string list with values

Initialize List of String in java

In this post, we will see how to initialize List of String in java.

Can you initialize List of String as below:

You can’t because List is an interface and it can not be instantiated with new List() .

You need to instantiate it with the class that implements the List interface.

Here are the common java Collections classes which implement List interface.

In most of the cases, you will initialize List with ArrayList as below.

If you are using java 7 or greater than you can use diamond operator with generics.

Initialize List of Strings with values

There are many ways to initialize list of Strings with values.

Arrays’s asList

You can use Arrays’s asList method to initialize list with values.

Stream.of (Java 8)

You can use java 8‘s Stream to initialize list of String with values.

List.of (Java 9)

Finally, java has introduced a of() method in List class to initialize list with values in java 9.

Using ArrayList’s add method

You can obviously initialize ArrayList with new operator and then use add method to add element to the list.

Using guava library

You can use guava library as well.

Here is the complete example.

That’s all about how to initialize List of String in java.

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Initialize List with Values in Java

In this tutorial, we’ll learn different ways to initialize List, ArrayList and LinkedList with values in single line in Java.

Java 8 or earlier

Initialize Immutable List

This is the simplest way to initialize a List:-

/** * Immutable list with inline elements */ ListString> list = Arrays.asList("foo", "bar", "baz");  /** * Immutable list with array */ String[] names =  "foo", "bar" >; ListString> anotherList = Arrays.asList(names);  anotherList.add("baz") // Throw UnsupportedOperationException exception 

The only drawback is that the initalized list is immutable. That means adding or removing elements in the list throw java.lang.UnsupportedOperationException exception.

It is useful when you just need it for iteration and read-only purpose.

Initialize Mutable List

If you want to intialize a mutable list where you can add or remove elements. You wrap immutable list with ArrayList or LinkedList :-

ListString> arrayList = new ArrayList<>(Arrays.asList("foo", "bar")); arrayList.add("baz"); // It works!  ListString> linkedList = new LinkedList<>(Arrays.asList("foo", "bar")); linkedList.remove("foo"); // It works! 

Collections.addAll()

You can also use Collections.addAll() static method to add values to ArrayList or LinkedList

ListString> arrayList = new ArrayListString>(); Collections.addAll(arrayList, "foo", "bar", "baz"); 

Double Brace Initialization

Another way is to making an anonymous inner class with an instance initializer. This is also known as an double brace initialization. However that looks like an overkill to create a inner class just to create an ArrayList or LinkedList

ListString> strings = new ArrayListString>()     add("A");  add("B");  add("C");  > >; 

Java 9 or later

Initialize Immutable List

List.of() is added in Java 9 which can be used to initialize an immutable list with values.

ListString> list = List.of("foo", "bar"); list.add("baz") // Throw UnsupportedOperationException exception 

With Java 10 or later, this can be even more shortened with the var keyword.

var list = List.of("foo", "bar", "baz"); 

Initialize Mutable List

You can also define mutable list with ArrayList or LinkedList wrapper:-

ListString> arrayList = new ArrayList<>(List.of("foo", "bar")); arrayList.add("baz"); // It works!  ListString> linkedList = new LinkedList<>(List.of("foo", "bar")); linkedList.remove("foo"); // It works! 

Using Streams

You can also use Stream API which is more flexible:-

StreamString> strings = Stream.of("foo", "bar", "baz"); 

You can combine two or more Streams like this:-

StreamString> strings = Stream.concat(Stream.of("foo", "bar"), Stream.of("baz", "qux")); 

You can transform a Stream into mutable List or ArrayList like this:-

ListString> list = Stream.of("foo", "bar", "baz").collect(Collectors.toList()); list.remove("baz"); // It works!  ListString> arrayList = Stream.of("foo", "bar").collect(Collectors.toCollection(ArrayList::new)); arrayList.add("baz"); // It works! 

See Also

Ashish Lahoti is a Software Engineer with 12+ years of experience in designing and developing distributed and scalable enterprise applications using modern practices. He is a technology enthusiast and has a passion for coding & blogging.

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Initialize List of String in Java

1. Use ArrayList , LinkedList and Vector to Instantiate a List of String in Java
2. Use Arrays.asList to Instantiate a List of String in Java
3. Use Stream in Java 8 to Instantiate a List of String in Java
4. Use List.of to Instantiate a List of String in Java

In this tutorial, we will see various ways in which we can Initialize a list of string in Java. Since the list is an interface, we can not directly instantiate it.

Use ArrayList , LinkedList and Vector to Instantiate a List of String in Java

A List is a child interface of Collections in Java. It is an ordered collection of objects which can store duplicate values. The instance of List can be created using classes that implement the List Interface.

ArrayList , Vector , LinkedList and Stack are a few of these classes. We create an instance myList of a List using new ArraList() . Hence, we can declare and create an instance of List using any of the following ways shown below and perform various operations on that List .

import java.util.ArrayList; import java.util.LinkedList; import java.util.List; import java.util.Vector;  public class ListExample   public static void main (String [] args )  ListString> myList = new ArrayListString>();  ListFruits> lList = new LinkedListFruits>();  ListInteger> vList = new VectorInteger>();   myList.add("Happy");  myList.add("Coding");   lList.add(new Fruits("Grapes", "Green"));  lList.add(new Fruits("Apple","Red"));   vList.add(1);  vList.add(4);  vList.add(9);  vList.add(7);   vList.remove(2);  for (String s :myList)   System.out.println(s);  >   for(Fruits f : lList )  System.out.println(f.name + " is " +f.color + " in color.");  >   for (int i : vList)  System.out.println(i);  >   >  > class Fruits   String name;  String color;  Fruits(String name , String color)  this.name = name;  this.color = color;  > > 

Happy Coding Grapes is Green in color. Apple is Red in color. 1 4 7 

Use Arrays.asList to Instantiate a List of String in Java

The Arrays.asList method returns a fixed-size list that is backed by an array. This is just a wrapper that makes the array available as a list. We can not modify this list as it is immutable.

Here in the code, we get an instance of List named myList whose length can not be modified.

import java.util.Arrays; import java.util.List;  public class ListExmp   public static void main(String[] args)   ListString> myList = Arrays.asList("John","Ben","Gregor","Peter");  String name = myList.get(3);  System.out.println(name);  > > 

Use Stream in Java 8 to Instantiate a List of String in Java

Java 8 Stream includes wrappers around a data source that makes a bulky process on the data easy and convenient.

The Stream.of() method constructs a stream of data and collects them in a list. The Collector interface provides the logic for this operation. The Collector.toList() collects all the stream elements into an instance of List .

import java.util.List; import java.util.stream.Stream; import java.util.stream.Collectors;  public class ListExmp   public static void main(String[] args)   ListString> list = Stream.of("john", "doe").collect(Collectors.toList());  if(list.contains("doe"))  System.out.println("doe is there");  >else  System.out.println("doe is not there");  >  > > 

Use List.of to Instantiate a List of String in Java

The List.of is the new method introduced in Java 9. In the code below, the List.of() method takes any number of arguments and returns an immutable list. We have immutableList as an unmodifiable instance of List .

We have to instantiate ArrayList with an immutable list as a parameter to create a mutable list. As shown in the code below, modifications can be made to the mutableList instance of the List .

import java.util.List; import java.util.ArrayList;  public class ListExmp   public static void main(String[] args)   ListString> immutableList = List.of("One","Two","Three","Four","Five");  ListString> mutableList = new ArrayList<>(List.of("Six", "Seven", "Eight"));  for(String l:immutableList)   System.out.println(l);  >  System.out.println("XXXXXX");  mutableList.add("Nine");  for(String l:mutableList)   System.out.println(l);  >  > > 

One Two Three Four Five XXXXXX Six Seven Eight Nine 

Rupam Saini is an android developer, who also works sometimes as a web developer., He likes to read books and write about various things.

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