List Sublist: extracts a sublist from an ArrayList

Problem Statement: Write a Java program that extracts a sublist from an ArrayList, given a start and end index.

Here’s a Java program that extracts a sublist from an ArrayList given start and end index.

package com.javacodepoint.collection;

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

public class ExtractSublistDemo {

	public static void main(String[] args) {
		ArrayList<String> originalList = new ArrayList<>();
		originalList.add("Apple");
		originalList.add("Banana");
		originalList.add("Cherry");
		originalList.add("Date");
		originalList.add("Fig");

		System.out.println("Original List: " + originalList);

		int startIndex = 1; // Inclusive
		int endIndex = 3; // Exclusive

		// Extracting a sublist
		List<String> sublist = extractSublist(originalList, startIndex, endIndex);

		System.out.println("Sublist from index " + startIndex + " to " + endIndex + ": " + sublist);
	}

	// Method to extract a sublist from an ArrayList
	public static <T> List<T> extractSublist(List<T> list, int startIndex, int endIndex) {
		if (startIndex < 0 || endIndex > list.size() || startIndex > endIndex) {
			throw new IllegalArgumentException("Invalid start or end index");
		}

		return list.subList(startIndex, endIndex);
	}
}

OUTPUT:

Original List: [Apple, Banana, Cherry, Date, Fig]
Sublist from index 1 to 3: [Banana, Cherry]

Explanation:

1. Creating the List: We create an ArrayList named originalList and populate it with some strings.
2. Printing the Original List: We print the contents of the originalList using System.out.println().
3. Defining Start and End Indices: We specify the startIndex (inclusive) and endIndex (Exclusive) to define the range of elements we want to extract from the originalList.
4. Extracting the Sublist: We call the extractSublist() method to extract the sublist from the originalList based on the given start and end indices.
5. extractSublist() Method: This method takes three parameters: the original list (list), the start index (startIndex), and the end index (endIndex).
6. Input Validation: Inside the method, we perform some input validation to ensure that the start index is not negative, the end index does not exceed the size of the list, and the start index is less than the end index. If any of these conditions are not met, an IllegalArgumentException is thrown.
7. Sublist Extraction: We use the subList() method provided by the List interface to extract the sublist based on the start and end indices. This method returns a view of the original list, containing the elements from the start index (inclusive) up to, but not including, the end index (exclusive).
8. Printing the Sublist: Finally, we print the contents of the extracted sublist.

By using the subList() method, the program effectively extracts a sublist from an ArrayList based on the specified start and end indices.

See also: Find duplicate elements in an ArrayList.