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:
Example
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:
Example
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:
Example
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 myNumbers
for (String i : cars) {
System.out.println(i);
}
}
}
Sort an ArrayList of Integers numerically in reverse/descending order:
Example
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);
}
}
}
