How to Create a Sorted List of Objects in Java?

Is it possible to have a sorted list of objects in Java?

List<Employee> employeeList = new ArrayList<>();
Collections.sort(employeeList, Comparator.comparing(Employee::getName));

In Java, you can easily create and manage a sorted list of objects using the Collections framework. The framework provides various data structures and utilities that allow you to sort objects based on specified criteria. Here’s how you can do this effectively.

import java.util.*;

public class Employee {
    private String name;
    private int age;

    public Employee(String name, int age) {
        this.name = name;
        this.age = age;
    }

    public String getName() {
        return name;
    }

    @Override
    public String toString() {
        return name + " (" + age + ")";
    }
}

class Main {
    public static void main(String[] args) {
        List<Employee> employees = new ArrayList<>();
        employees.add(new Employee("Alice", 30));
        employees.add(new Employee("Bob", 25));
        employees.add(new Employee("Charlie", 28));

        Collections.sort(employees, Comparator.comparing(Employee::getName));

        for (Employee employee : employees) {
            System.out.println(employee);
        }
    }
}

Causes

• Default order using Comparable interface.
• Custom order using Comparator interface.
• Natural ordering based on object properties.

Solutions

• Use Collections.sort() with a Comparator for custom sorting.
• Implement Comparable in your class for default sorting.
• Utilize TreeSet for automatically sorted collections.

Mistake: Not implementing Comparable in your custom objects.

Solution: Ensure your class implements Comparable or use Comparator to define ordering.

Mistake: Sorting with null values in the list.

Solution: Check and handle null values before sorting to avoid NullPointerException.