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.