How to Initialize an ArrayList in Java

In this tutorial, we'll see 4 methods to initialize an ArrayList in Java with examples:

1) Arrays.asList

The method Arrays.asList takes a list of objects as input o1, o2...,on. Its syntax is as follows:

ArrayList arlist = new ArrayList(Arrays.asList(Object o1, Object o2,...,Object on));

Example:

import java.util.ArrayList; 
import java.util.Arrays; 
import java.util.List; 

public class Initialise {
 public static void main (String args[]) {

 // create an array of String
 String a[] = new String[]{"a","b","c","d"}; 
 
 ArrayList arlist = new ArrayList(Arrays.asList(a)); 

 // Show objects
 System.out.println(arlist); 
 }
}

Output:

[a, b, c, d]

2) Method add()

add(E e) is the basic method for adding items to an ArrayList.

< div>Example:

import java.util.ArrayList; 

public class Initialise {
 public static void main (String args[]) {

 ArrayList arlist = new ArrayList(Arrays.asList(a)); 

 arlist.add("a"); 
 arlist.add("b"); 
 arlist.add("c"); 
 arlist.add("d"); 
 
 System.out.println(arlist); 
 }
}

Output:

[a, b, c, d]

3) Collections.ncopies

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

public class Initialise {
public static void main (String args[]) {

ArrayList list = new ArrayList(Collections.nCopies(5, "a"));
System.out.println(list);

}
}

4) Anonymous class

ArrayList arlist = new ArrayList(){{
add(o1);
add(o2);
add(o3);
...
...
}};

import java.util.ArrayList;

public class Initialise {
public static void main (String args[]) {
ArrayList country = new ArrayList(){{
add("turkey");
add("Malaysia");
add("france");
}};
System.out.println(country);
}
}

[Turkey, Malaysia, France]