Java List Sorting: Methods and Examples

Introduce Java List Sorting and give examples

In Java, the List interface is part of the Java Collections Framework and represents an ordered collection (also known as a sequence). The List interface provides various methods to manipulate the elements in the list, including sorting. Sorting a list can be done using the Collections.sort() method or the List.sort() method, both of which allow you to sort the elements in natural order or using a custom comparator.

Sorting a List in Java

1. Using Collections.sort(): The Collections.sort() method sorts the specified list into ascending order, according to the natural ordering of its elements.

   Example:

   import java.util.ArrayList;
   import java.util.Collections;
   import java.util.List;
   
   public class ListSortingExample {
       public static void main(String[] args) {
           List<String> fruits = new ArrayList<>();
           fruits.add("Banana");
           fruits.add("Apple");
           fruits.add("Orange");
           fruits.add("Mango");
   
           // Sorting the list in natural order
           Collections.sort(fruits);
   
           System.out.println("Sorted fruits: " + fruits);
       }
   }
   

   Output:

   Sorted fruits: [Apple, Banana, Mango, Orange]
   

2. Using List.sort(): The List.sort() method is a default method in the List interface that sorts the list using a specified comparator.

   Example:

   import java.util.ArrayList;
   import java.util.Comparator;
   import java.util.List;
   
   public class ListSortingWithComparator {
       public static void main(String[] args) {
           List<String> fruits = new ArrayList<>();
           fruits.add("Banana");
           fruits.add("Apple");
           fruits.add("Orange");
           fruits.add("Mango");
   
           // Sorting the list in reverse order using a comparator
           fruits.sort(Comparator.reverseOrder());
   
           System.out.println("Sorted fruits in reverse order: " + fruits);
       }
   }
   

   Output:

   Sorted fruits in reverse order: [Orange, Mango, Banana, Apple]
   

3. Sorting a List of Custom Objects: You can also sort a list of custom objects by implementing the Comparable interface or by using a Comparator.

   Example:

   import java.util.ArrayList;
   import java.util.Collections;
   import java.util.Comparator;
   import java.util.List;
   
   class Person {
       String name;
       int age;
   
       Person(String name, int age) {
           this.name = name;
           this.age = age;
       }
   
       @Override
       public String toString() {
           return name + " (" + age + ")";
       }
   }
   
   public class CustomObjectSorting {
       public static void main(String[] args) {
           List<Person> people = new ArrayList<>();
           people.add(new Person("Alice", 30));
           people.add(new Person("Bob", 25));
           people.add(new Person("Charlie", 35));
   
           // Sorting by age using a comparator
           Collections.sort(people, Comparator.comparingInt(person -> person.age));
   
           System.out.println("Sorted people by age: " + people);
       }
   }
   

   Output:

   Sorted people by age: [Bob (25), Alice (30), Charlie (35)]
   

Summary

• You can sort lists in Java using Collections.sort() or List.sort().
• Sorting can be done in natural order or using custom comparators.
• You can sort lists of custom objects by implementing the Comparable interface or by providing a Comparator.

These methods provide a flexible way to sort data in Java applications.