How to sort an ArrayList in Ascending Order in Java

ArrayList stores elements in insertion order in java. However, in many real-world scenarios, we need to sort the elements-for example, sorting names alphabetically or numbers in increasing order. In this article, we will learn how to sort an ArrayList in ascending order in Java using built-in utilities.

Example:

Input: Unsorted ArrayList: [Geeks, For, ForGeeks, GeeksForGeeks, A computer portal]
Output: Sorted ArrayList: [A computer portal, For, ForGeeks, Geeks, GeeksForGeeks]

1. Using Collections.sort()

Java provides the Collections.sort() method to sort a list according to the natural ordering of its elements.

• For String objects, natural order means lexicographical (dictionary) order
• The sorting is done in-place, meaning the original list is modified

import java.util.*;

public class GFG {
    public static void main(String[] args) {
        ArrayList<String> list = new ArrayList<>();

        list.add("Geeks");
        list.add("For");
        list.add("ForGeeks");
        list.add("GeeksForGeeks");
        list.add("A computer portal");

        System.out.println("Unsorted ArrayList: " + list);
        Collections.sort(list);
        System.out.println("Sorted ArrayList in Ascending order: " + list);
    }
}

Unsorted ArrayList: [Geeks, For, ForGeeks, GeeksForGeeks, A computer portal]
Sorted ArrayList in Ascending order: [A computer portal, For, ForGeeks, Geeks, GeeksForGeeks]

Explanation:

• An ArrayList<String> is created and populated with string values
• Collections.sort(list) sorts the elements based on their natural ordering
• The method modifies the original list and does not return a new one
• The sorted result is printed to the console

2. Using ArrayList.sort() Method

From Java 8 onwards, the List interface provides the sort() method, making sorting more object-oriented and readable.

import java.util.*;

public class GFG {
    public static void main(String[] args) {
        ArrayList<String> list = new ArrayList<>(
            Arrays.asList("Geeks", "For", "ForGeeks", "GeeksForGeeks", "A computer portal")
        );
        list.sort(null); // natural ascending order
        System.out.println("Sorted ArrayList: " + list);
    }
}

Sorted ArrayList: [A computer portal, For, ForGeeks, Geeks, GeeksForGeeks]

Explanation:

• sort(null) uses natural ordering
• Works similar to Collections.sort()
• Preferred in modern Java code

3. Using Collections.sort() with Comparator

A Comparator allows explicit control over sorting logic. For ascending order, we can use Comparator.naturalOrder().

import java.util.*;

public class GFG {
    public static void main(String[] args) {
        ArrayList<String> list = new ArrayList<>();

        list.add("Geeks");
        list.add("For");
        list.add("ForGeeks");

        Collections.sort(list, Comparator.naturalOrder());
        System.out.println("Sorted ArrayList: " + list);
    }
}

Sorted ArrayList: [For, ForGeeks, Geeks]

Why use this?

• Makes sorting logic explicit
• Helpful when switching between ascending and descending order

4. Sorting an ArrayList of Numbers in Ascending Order

The same approaches work for numeric data types.

import java.util.*;

public class GFG {
    public static void main(String[] args) {
        ArrayList<Integer> numbers = new ArrayList<>(
            Arrays.asList(5, 2, 9, 1, 3)
        );
        Collections.sort(numbers);
        System.out.println("Sorted Numbers: " + numbers);
    }
}