Java List Sorting

Java Sort a List

In the previous chapters, you learned how to use two popular lists in Java: ArrayList and LinkedList, which are found in the java.util package.

Another useful class in the java.util package is the Collections class, which include the sort() method for sorting lists alphabetically or numerically.

Sort an ArrayList

Sort an ArrayList of Strings alphabetically in ascending order:

import java.util.ArrayList;
import java.util.Collections;  // Import the Collections class

public class Main {
  public static void main(String[] args) {
    ArrayList<String> cars = new ArrayList<String>();
    cars.add("Volvo");
    cars.add("BMW");
    cars.add("Ford");
    cars.add("Mazda");

    Collections.sort(cars);  // Sort cars

    for (String i : cars) {
      System.out.println(i);
    }
  }
}

Sort an ArrayList of Integers numerically in ascending order:

import java.util.ArrayList;
import java.util.Collections;  // Import the Collections class

public class Main {
  public static void main(String[] args) {
    ArrayList<Integer> myNumbers = new ArrayList<Integer>();
    myNumbers.add(33);
    myNumbers.add(15);
    myNumbers.add(20);
    myNumbers.add(34);
    myNumbers.add(8);
    myNumbers.add(12);

    Collections.sort(myNumbers);  // Sort myNumbers

    for (int i : myNumbers) {
      System.out.println(i);
    }
  }
}

Reverse the Order

You can also sort a list in reverse order, by using the reverseOrder() method.

In the following example, we sort an ArrayList of Strings alphabetically in reverse/descending order:

import java.util.ArrayList;
import java.util.Collections;  // Import the Collections class

public class Main {
  public static void main(String[] args) {
    ArrayList<String> cars = new ArrayList<String>();
    cars.add("Volvo");
    cars.add("BMW");
    cars.add("Ford");
    cars.add("Mazda");

    Collections.sort(cars, Collections.reverseOrder()); // Sort cars

    for (String i : cars) {
      System.out.println(i);
    }
  }
}

Sort an ArrayList of Integers numerically in reverse/descending order:

import java.util.ArrayList;
import java.util.Collections;  // Import the Collections class

public class Main {
  public static void main(String[] args) {
    ArrayList<Integer> myNumbers = new ArrayList<Integer>();
    myNumbers.add(33);
    myNumbers.add(15);
    myNumbers.add(20);
    myNumbers.add(34);
    myNumbers.add(8);
    myNumbers.add(12);

    Collections.sort(myNumbers, Collections.reverseOrder()); // Sort myNumbers

    for (int i : myNumbers) {
      System.out.println(i);
    }
  }
}