Sorting a List: Sort an ArrayList of integers

Problem Statement: Implement a Java program to sort an ArrayList of integer numbers.

Here’s a Java program that demonstrates how to sort an ArrayList of integers using the built-in Collections.sort() method. I’ll provide you with an explanation of the program’s logic.

package com.javacodepoint.collection;

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

public class SortArrayListDemo {
	
	public static void main(String[] args) {
		List<Integer> numbers = new ArrayList<>();
		numbers.add(5);
		numbers.add(2);
		numbers.add(8);
		numbers.add(1);
		numbers.add(3);

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

		// Sorting the ArrayList
		Collections.sort(numbers);

		System.out.println("Sorted List: " + numbers);
	}
}

OUTPUT:

Original List: [5, 2, 8, 1, 3]
Sorted List: [1, 2, 3, 5, 8]

Explanation:

1. Import Statements: We import the necessary classes, including ArrayList, List, and Collections from the java.util package.
2. Creating the List: We create an ArrayList named numbers and populate it with some integers.
3. Printing the Original List: We print the contents of the numbers list using System.out.println().
4. Sorting the List: We use the Collections.sort() method to sort the numbers list in ascending order. This method sorts the list in place, meaning it modifies the original list rather than creating a new sorted list.
5. Printing the Sorted List: We print the contents of the sorted numbers list using System.out.println().

By calling Collections.sort(numbers), we sort the ArrayList of integers in ascending order. The result is a list of integers that have been rearranged from their original order. The Collections.sort() method works for any List of objects that implement the Comparable interface, which includes the built-in types like Integer.

See also: Find duplicate elements in an ArrayList.