Get Sublist of an ArrayList Using Java

In Java, an ArrayList is a class of the List interface, which stores elements of similar data types and can be null while creating.

A sub-list is the view of a portion (or part) of an ArrayList. For example, if the given array list is {1, 2, 3, 4, 5}, then the possible sub-lists can be {1, 2}, {1, 2, 3}, {2, 3, 4}, {4, 5}, etc.

The List interface in Java provides a built-in method named subList(), which directly returns a sub-list from the given ArrayList.

Sublist from an ArrayList using the subList() Method

The subList() method of the List interface returns a portion (i.e., sub-list) of the original list between the specified range, which is fromIndex to toIndex. In the obtained sub-list, the element at fromIndex will be included, and at toIndex will be excluded.

Following is the syntax of the subList() method:

List<E> subList(int fromIndex, int toIndex)

Here,

• fromIndex: The starting index (inclusive) from which the sub-list will begin extracting elements.
• toIndex: The last index (not included) up to which the sub-list will be extracted.

Example

In the following example, we use the subList() method to get a sub-list from an ArrayList {10, 20, 30, 40, 50} between the specified range 1 to 5:

import java.util.ArrayList;
import java.util.List;
public class findElement {
   public static void main(String[] args) {
   
      //creating an ArrayList
      ArrayList<Integer> list = new ArrayList<>();
      
      //adding elements
      list.add(10);
      list.add(20);
      list.add(30);
      list.add(40);
      list.add(50);
      
      System.out.println("The original ArrayList is: " + list);
      
      //range
      int fromIndex = 1;
      int toIndex = 4;
      System.out.println("The range is: " + fromIndex + ", " + toIndex);
      
      // Get the subList using subList() method
      List<Integer> subList = list.subList(fromIndex, toIndex);
      System.out.println("The sublist elements are: " + subList);
   }
}

Below is the output of the above program:

The original ArrayList is: [10, 20, 30, 40, 50]
The range is: 1, 4
The sublist elements are: [20, 30, 40]

Adding an ArrayList Element to another ArrayList

We can get a sub-list by adding a specific range of elements from one ArrayList to another ArrayList. The resultant ArrayList will be the desired sub-list.

The add() method of the List interface appends the specified element to the end of the list. Therefore, to get a sublist of an ArrayList, we need to iterate through the (original) ArrayList at any position using a for loop and add those elements to a new ArrayList (i.e., sub-list) using the add() method.

Example

In the example below, we add elements from the original ArrayList to a new ArrayList (i.e., sub-list) from index 2. To do this, we iterate through the original ArrayList starting from index 2 and add each element to the sub-list using the add() method.

import java.util.ArrayList;
public class findElement {
   public static void main(String[] args) {

      //creating an ArrayList
      ArrayList<Integer> list = new ArrayList<>();

      //adding elements
      list.add(1);
      list.add(2);
      list.add(3);
      list.add(4);
      list.add(5);

      System.out.println("The original ArrayList is: " + list);

      //creating another ArrayList
      ArrayList<Integer> subList = new ArrayList<>();
      for(int i = 2; i<list.size(); i++){
         subList.add(list.get(i));
      }
      
      System.out.println("The subList elements are: " + subList);
   }
}

Following is the output of the above program:

The original ArrayList is: [1, 2, 3, 4, 5]
The subList elements are: [3, 4, 5]