Sorting a list using Collections

Sort Employee Objects on Age

MallikLeave a comment

This program defines an Employee class with properties of name, id, and age, and implements the Comparable interface to enable sorting by age. The main method creates a list of 100 employee objects and sorts them based on age using the Collections.sort method. Finally, the sorted list of employees is printed to the console.

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

public class Employee implements Comparable<Employee> {
    private String name;
    private String id;
    private int age;

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

    public String getName() {
        return name;
    }

    public String getId() {
        return id;
    }

    public int getAge() {
        return age;
    }

    @Override
    public int compareTo(Employee other) {
        return Integer.compare(this.age, other.age);
    }

    @Override
    public String toString() {
        return "Employee{" +
                "name='" + name + '\'' +
                ", id='" + id + '\'' +
                ", age=" + age +
                '}';
    }

    public static void main(String[] args) {
        // Create a list of 100 employee objects
        List<Employee> employees = new ArrayList<>();
        employees.add(new Employee("John", "1001", 25));
        employees.add(new Employee("Jane", "1002", 30));
        employees.add(new Employee("Bob", "1003", 28));
        // ... and so on for the other 97 employees

        // Sort the list of employees based on age (ascending order)
        Collections.sort(employees);
        System.out.println(employees);
    }
}

Different ways of sorting an User Object

MallikLeave a comment

There are many ways to sort a java object but it is very hard to figure out which one is more efficient. Here is an example which describes different ways of executing sorting mechanism for User object based on age.

Try to run this application in you local machine to see which method is more efficient and good to use in our regular programming life.

package com.malliktalksjava.java8;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

import static java.util.stream.Collectors.toList;

public class SortingExampleUser {

    public static void main(String[] args) {
        List<User> userList = new ArrayList<>();
        userList.add(new User("Ram", 28));
        userList.add(new User("Raj", 35));
        userList.add(new User("Rakesh", 31));
        userList.add(new User("Peter", 30));
        userList.add(new User("John", 25));
        userList.add(new User("Sri", 55));

        long starttime = System.currentTimeMillis();
        System.out.println("sortListUsingCollections : " + sortListUsingCollections(userList));
        System.out.println("Time Taken in Millis : " + (System.currentTimeMillis() - starttime));

        long starttime2 = System.currentTimeMillis();
        System.out.println("sortListUsingCollections : " + sortListUsingStreams(userList));
        System.out.println("Time Taken in Millis  2: " + (System.currentTimeMillis() - starttime2));

        long starttime3 = System.currentTimeMillis();
        System.out.println("sortListUsingCollections : " + sortUsingLambda(userList));
        System.out.println("Time Taken in Millis  2: " + (System.currentTimeMillis() - starttime3));


    }


    //using Collections.sort
    private static List<User> sortListUsingCollections(List<User> list){

        Collections.sort(list, Comparator.comparingInt(User::getAge));
        //Collections.reverse(list); // un comment if for descending order

        return list;
    }

    //using streams and comparator
    private static List<User> sortListUsingStreams(List<User> list){

        return list.stream()
                .sorted(Comparator.comparingInt(User::getAge))
                //.sorted(Comparator.comparingInt(User::getAge).reversed()) //-- for reverse order uncomment this line and comment above line
                .collect(toList());
    }

    //using lambda expressions
    private static List<User> sortUsingLambda(List<User> list){

        return list.stream()
                .sorted((User user1, User user2) -> user1.getAge() > user2.getAge() ? 1: 0)
                //.sorted((User user1, User user2) -> user1.getAge() < user2.getAge() ? 1: 0) - uncomment if reverse order needed
                .collect(toList());

    }
}

class User{
    private String name;
    private int age;

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

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    @Override
    public String toString() {
        return "User{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
}