How to sort ArrayList in Java

In this tutorial, you will learn how to sort ArrayList in Java. We will see java programs in this guide, to sort an ArrayList in ascending and descending order.

What is an ArrayList?

Arraylist is a class in java that implements List interface. It is based on an Array data structure. It is widely used because of the functionality and flexibility it offers. Most of the developers choose Arraylist over Array as ArrayList can dynamically grow and shrink after addition and removal of elements.

This is how an ArrayList looks like:

[Shyam, Chaitanya, Steve, Ram]

After sorting this ArrayList in ascending order:

[Chaitanya, Ram, Shyam, Steve]

After sorting the original ArrayList in descending order:

[Steve, Shyam, Ram, Chaitanya]

Example 1: Sorting ArrayList in Ascending order

In this example, we have an ArrayList of String type. We are sorting the given ArrayList in ascending order using Collections.sort() method. Since this ArrayList is of string type, the elements are sorted in ascending alphabetical order.

import java.util.*;
public class JavaExample {
  public static void main(String args[]){
    ArrayList<String> listOfCountries = new ArrayList<>();
    listOfCountries.add("India");
    listOfCountries.add("US");
    listOfCountries.add("China");
    listOfCountries.add("Denmark");

    // Original unsorted list
    System.out.println("Before Sorting: "+ listOfCountries);

    //Sorting the ArrayList using sort() method
    Collections.sort(listOfCountries);

    // Printing sorted ArrayList
    System.out.println("After Sorting: "+ listOfCountries);
  }
}

Output:

Example 2: Sorting ArrayList of Integer Type

In this example, we have an ArrayList of integers and we are sorting it using the sort() method. This program is similar to the above program except that the list is of integer type here so the ArrayList elements are integers.

import java.util.*;
public class JavaExample{

  public static void main(String args[]){
    ArrayList<Integer> arraylist = new ArrayList<>();
    arraylist.add(11);
    arraylist.add(2);
    arraylist.add(7);
    arraylist.add(3);

    //Before sorting
    System.out.println("Before Sorting: "+ arraylist);

    // Sorting the list of integers using sort() method
    Collections.sort(arraylist);

    //After sorting
    System.out.println("After Sorting: "+ arraylist);
  }
}

Output:

Before Sorting: [11, 2, 7, 3]
After Sorting: [2, 3, 7, 11]

Example 3: Sorting an ArrayList in Descending order

In this program, we are sorting the given ArrayList in descending order. To sort an ArrayList in descending order, we just have to pass the Collection.reverseOrder() as a second parameter in the Collections.sort() method as shown below. Similarly, we can sort an ArrayList of integer type in descending order as well.

import java.util.*;
public class JavaExample{

  public static void main(String args[]){
    ArrayList<String> arraylist = new ArrayList<>();
    arraylist.add("Apple");
    arraylist.add("Orange");
    arraylist.add("Kiwi");
    arraylist.add("Banana");
    arraylist.add("Mango");

    //Before sorting
    System.out.println("Before Sorting: "+ arraylist);

    // Sorting the list in descending order
    Collections.sort(arraylist, Collections.reverseOrder());

    //After sorting
    System.out.println("After Sorting: "+ arraylist);
  }
}

Output:

Example 4: Sort ArrayList entered by user in descending order

In this example, user is asked to enter the size of ArrayList. This is read and stored in an int variable size. A while loop runs to read and add the user entered elements to the ArrayList. Once the list is populated with the user entered elements, the list is sorted in reverse order by using the sort() method similar to the Example 3.

import java.util.*;
public class JavaExample {
  public static void main(String[] args) {
    int i=0, size;
    Scanner scan = new Scanner(System.in);
    ArrayList<String> list = new ArrayList<>();

    System.out.println("How many elements you want in list? ");
    size = scan.nextInt();
    Scanner scan2 = new Scanner(System.in);
    System.out.println("Enter elements: ");
    while(i<size)
    {
      list.add(scan2.nextLine());
      i++;
    }

    //Before sorting
    System.out.println("Before Sorting: "+ list);

    // Sorting the list in descending order
    Collections.sort(list, Collections.reverseOrder());

    //After sorting
    System.out.println("After Sorting: "+ list);
  }
}

Output:

Related guides:

1. Sort ArrayList in descending order
2. Sort ArrayList of Objects using Comparable and Comparator