How to get sublist of an ArrayList with example

In this tutorial, we will see how to get a sublist from an existing ArrayList. We will be using the subList() method of ArrayList class.

Syntax:

List subList(int fromIndex, int toIndex)

Here fromIndex is inclusive and toIndex is exclusive. There are few important points regarding this method which I have shared at the end of this post.

Note:
The subList method throws IndexOutOfBoundsException – if the specified indexes are out of the range of ArrayList (fromIndex < 0 || toIndex > size).
IllegalArgumentException – if the starting index is greater than the end point index (fromIndex > toIndex).

Example 1: Getting a sublist from an ArrayList

In the following example, we have an ArrayList al. We want to get a sublist starting from index 1 till index 3 from this ArrayList. To get this sublist, we are calling the subList() method like this: al.subList(1, 4).

As mentioned in the syntax of sublist(), the fromIndex is inclusive and toIndex is exclusive, which means index 1 is inclusive and index 4 is exclusive. This is why element present at index 1 is included in sublist, while element present at index 4 is excluded from ArrayList and elements are present till index 3.

We placed the code inside a try-catch block to catch any exception. In this program, indexes mentioned in the subList() method are valid so no exception raised. In the example 2 and 3, we will see how to handle exception when index values are invalid.

import java.util.ArrayList;
import java.util.List;
public class JavaExample {

  public static void main(String a[]){
    try {
      ArrayList<String> al = new ArrayList<String>();

      //Addition of elements in ArrayList
      al.add("Steve");
      al.add("Justin");
      al.add("Ajeet");
      al.add("John");
      al.add("Arnold");
      al.add("Chaitanya");

      System.out.println("Original ArrayList Content: " + al);

      //Storing Sublist into another ArrayList
      ArrayList<String> al2 = new ArrayList<String>(al.subList(1, 4));
      System.out.println("SubList stored in ArrayList: " + al2);

      //Storing Sublist into a List
      List<String> list = al.subList(1, 4);
      System.out.println("SubList stored in List: " + list);
    }
    catch (IndexOutOfBoundsException e) {
      System.out.println("Exception while getting sublist: " + e);
    }

    catch (IllegalArgumentException e) {
      System.out.println("Exception while getting sublist: " + e);
    }
  }
}

Output:

Original ArrayList Content: [Steve, Justin, Ajeet, John, Arnold, Chaitanya]
SubList stored in ArrayList: [Justin, Ajeet, John]
SubList stored in List: [Justin, Ajeet, John]

Example 2: subList() method: IndexOutOfBoundsException

As mentioned in the beginning, if the specified indexes in subList() method are out of the range, this method throws IndexOutOfBoundsException. Exception occurs if index values satisfies this condition: (fromIndex < 0 || toIndex > size)

import java.util.ArrayList;
import java.util.List;
public class JavaExample {

  public static void main(String a[]){
    try {
      ArrayList<String> al = new ArrayList<String>();

      //Addition of elements in ArrayList
      al.add("Steve");
      al.add("Justin");
      al.add("Ajeet");
      al.add("John");
      al.add("Arnold");
      al.add("Chaitanya");

      System.out.println("Original ArrayList Content: " + al);

      // The toIndex is 14 and size of the ArrayList is 6 so
      // toIndex > size, this will throw exception
      List<String> list = al.subList(1, 14);
      System.out.println("SubList: " + list);
    }
    catch (IndexOutOfBoundsException e) {
      System.out.println("Exception while getting sublist: " + e);
    }

    catch (IllegalArgumentException e) {
      System.out.println("Exception while getting sublist: " + e);
    }
  }
}

Output:

Example 3: subList() method: IllegalArgumentException

If the starting index is greater than the end index (fromIndex > toIndex) then IllegalArgumentException occurs. Let’s see the following example to understand when this exception occurs.

import java.util.ArrayList;
import java.util.List;
public class JavaExample {

  public static void main(String a[]){
    try {
      ArrayList<String> names = new ArrayList<String>();

      //Addition of elements in ArrayList
      names.add("Paul");
      names.add("Rahul");
      names.add("Kevin");
      names.add("Smith");
      names.add("Rob");

      System.out.println("Original ArrayList Content: " + names);

      // Here fromIndex is 4 and toIndex is 2
      // fromIndex > toIndex, this will throw exception
      List<String> list = names.subList(4, 2);
      System.out.println("SubList: " + list);
    }
    catch (IndexOutOfBoundsException e) {
      System.out.println("Exception while getting sublist: " + e);
    }

    catch (IllegalArgumentException e) {
      System.out.println("Exception while getting sublist: " + e);
    }
  }
}

Output:

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• Difference between Array and ArrayList
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