In this post we will see how to initialize an ArrayList in Java with examples. I have already discussed how to sort ArrayList and how to find length of an ArrayList in Java. There are 4 ways to achieve our goal:

1. Using add() method
2. Using Arrays.asList() method
3. Using Anonymous inner class method
4. Using Collections.nCopies() method

Read Also: How to Reverse an ArrayList in Java

Initialize ArrayList in Java

Method 1: Using add() method


Syntax:

a. Initialize ArrayList of String using add() method:

ArrayList<String> al = new ArrayList();
al.add("String1");
al.add("String2");
al.add("String3");

b. Initialize ArrayList of Integer using add() method:

ArrayList<Integer> al2 = new ArrayList();
al2.add(Integer1);
al2.add(Integer2);
al2.add(Integer3);

Example:

Given below is the example of initializing ArrayList using add() method:

import java.util.*;

 public class ArrayListInitialization {
    public static void main(String args[]) {
        ArrayList<String> cars = new ArrayList();
        cars.add("Honda");
        cars.add("Hyundai");
        cars.add("Toyota");
        System.out.println("Cars stored in ArrayList are: "+ cars);
  }
}


Output:
Cars stored in ArrayList are: [Honda, Hyundai, Toyota]

Method 2: Using Arrays.asList() method


Syntax:

a. Initialize ArrayList of String using Arrays.asList() method:

ArrayList<String> al = new ArrayList(Arrays.asList("String1","String2","String3"));

b. Initialize ArrayList of Integer using Arrays.asList() method:

ArrayList<Integer> al2 = new ArrayList(Arrays.asList(Integer1, Integer2, Integer3));

Example:

Given below is the example of initializing ArrayList using Arrays.asList() method:

import java.util.*;

 public class ArrayListInitialization2 {
    public static void main(String args[]) {
       ArrayList<String> al = new ArrayList(Arrays.asList("Boston", "Chicago", "Dallas"));
       System.out.println("Elements are: "+ al);
  }
}


Output:
Elements are: [Boston, Chicago, Dallas]

Method 3: Using Anonymous inner class method


Syntax:

Initialize ArrayList of String using Anonymous inner class method:

ArrayList<String> al = new ArrayList(){{
            add("String1");
            add("String2");
            add("String3");
            add("String4");
        }};


Example:

Given below is the example of initializing ArrayList using anonymous inner class method:


import java.util.ArrayList;

public class ArrayListInitialization3 {
    public static void main(String args[]) {
        ArrayList<String> al = new ArrayList(){{
            add("Facebook");
            add("TikTok");
            add("Twitter");
            add("Snapchat");
        }}; 
        System.out.println("Best social media platforms are: "+ al);
    }
}


Output:
Best social media platforms are: [Facebook, TikTok, Twitter, Snapchat]

Method 4: Using Collections.nCopies() method


Syntax:

a. Initialize ArrayList of String using Collections.nCopies() method:

ArrayList<String> al = new ArrayList(Collections.nCopies(count, element));


Example:

Given below is the example of initializing ArrayList using Collections.nCopies():


import java.util.ArrayList;
import java.util.Collections;

public class ArrayListInitialization4 {
    public static void main(String args[]) {
        ArrayList<String> al = new ArrayList(Collections.nCopies(7, 7));
        System.out.println("nCopies prints elements are: "+ al);
    }
}


Output:
nCopies prints elements are: [7, 7, 7, 7, 7, 7, 7]

That's all for today. Please mention in the comments if you know any other way of initializing an ArrayList in Java.