Java ArrayList sort() method usage and example

Java ArrayList Methods

The Java ArrayList sort() method sorts the elements in the arraylist according to the specified order.

The syntax of the sort() method is:

arraylist.sort(Comparator c)

sort() parameter

• comparator - Specify the sorting order of the arraylist

sort() return value

The sort() method does not return any value. It only changes the order of elements in the ArrayList.

Example1Sort the ArrayList in natural order

import java.util.ArrayList;
import java.util.Comparator;
class Main {
　　public static void main(String[] args) {
　　　　//Create ArrayList
　　　　ArrayList<String> languages = new ArrayList<>();
　　　　//Add elements to the ArrayList
　　　　languages.add("Python");
　　　　languages.add("Swift");
　　　　languages.add("C");
　　　　languages.add("JavaScript");
　　　　System.out.println("Unsorted ArrayList: ",　+　languages);
　　　　//Sort ArrayList in Ascending Order
　　　　languages.sort(Comparator.naturalOrder());
　　　　System.out.println("Sorted ArrayList: ",　+　languages);
　　}
}

Output Result

Unsorted ArrayList: [Python, Swift, C, JavaScript]
Sorted ArrayList: [C, JavaScript, Python, Swift]

In the above example, we used the sort() method to sort the ArrayList named languages. Note this line,

languages.sort(Comparator.naturalOrder());

Here, the naturalOrder() method of the Java Comparator interface specifies that elements are sorted in natural order (i.e., ascending).

The Comparator interface also provides a method to sort elements in descending order. For example,

Example2Sort the ArrayList in descending order

import java.util.ArrayList;
import java.util.Comparator;
class Main {
　　public static void main(String[] args) {
　　　　//Create ArrayList
　　　　ArrayList<String> languages = new ArrayList<>();
　　　　//Add elements to the ArrayList
　　　　languages.add("Python");
　　　　languages.add("Swift");
　　　　languages.add("C");
　　　　languages.add("JavaScript");
　　　　System.out.println("Unsorted ArrayList: ",　+　languages);
　　　　//Sort ArrayList in Ascending Order
　　　　languages.sort(Comparator.reverseOrder());
　　　　System.out.println("Sorted ArrayList: ",　+　languages);
　　}
}

Output Result

Unsorted ArrayList: [Python, Swift, C, JavaScript]
Sorted ArrayList: [Swift, Python, JavaScript, C]

Here, the reverseOrder() method of the Comparator interface specifies that the elements are sorted in reverse order (i.e., descending).

Note:Collections.sort()A more convenient method to sort an ArrayList.

Java ArrayList Methods