In the last post we discussed about class ArrayList in Java and its important methods. Here we are sharing multiple ways to initialize an ArrayList with examples.
Method 1: Initialization using Arrays.asList
Syntax:
ArrayList obj = new ArrayList[ Arrays.asList[Object o1, Object o2, Object o3, ....so on]];Example:
import java.util.*; public class InitializationExample1 { public static void main[String args[]] { ArrayList obj = new ArrayList[ Arrays.asList["Pratap", "Peter", "Harsh"]]; System.out.println["Elements are:"+obj]; } }Output:
Method 2: Anonymous inner class method to initialize ArrayList
Syntax:
ArrayList obj = new ArrayList[]{{ add[Object o1]; add[Object o2]; add[Object o3]; ... ... }};Example:
import java.util.*; public class InitializationExample2 { public static void main[String args[]] { ArrayList cities = new ArrayList[]{{ add["Delhi"]; add["Agra"]; add["Chennai"]; }}; System.out.println["Content of Array list cities:"+cities]; } }Output:
Content of Array list cities:[Delhi, Agra, Chennai]Method3: Normal way of ArrayList initialization
Syntax:
Example:
import java.util.*; public class Details { public static void main[String args[]] { ArrayList books = new ArrayList[]; books.add["Java Book1"]; books.add["Java Book2"]; books.add["Java Book3"]; System.out.println["Books stored in array list are: "+books]; } }Output:
Books stored in array list are: [Java Book1, Java Book2, Java Book3]Method 4: Use Collections.ncopies
Collections.ncopies method can be used when we need to initialize the ArrayList with the same value for all of its elements. Syntax:count is number of elements and element is the item value
ArrayList obj = new ArrayList[Collections.nCopies[count, element]];Example:
import java.util.*; public class Details { public static void main[String args[]] { ArrayList intlist = new ArrayList[Collections.nCopies[10, 5]]; System.out.println["ArrayList items: "+intlist]; } }Output:
ArrayList items: [5, 5, 5, 5, 5, 5, 5, 5, 5, 5]