Java List Sorting: Methods and Examples

Answer:

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

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]

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]

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.

Java List Sorting: Methods and Examples

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Sorting a List in Java

Summary