Collections Of Classes

ArrayList and List are array-like collections. Unlike arrays, the elements count can be dynamic - there is no need to specify it.

ArrayList

Package to import

Creation syntax

Example

import java.util.ArrayList;

class Car
{
    private String model;
    private double price;

Car(String model, double price)
    {
        this.model = model;
        this.price = price;
    }

public void printData()
    {
        System.out.println("Model: " + this.model);
        System.out.println("Price: " + this.price);
    }
}

class CarDealership
{
    public ArrayList<Car> cars;

CarDealership()
    {
        System.out.println("ArrayList creation.");

// Create ArrayList of cars:
        this.cars = new ArrayList<Car>();
    }
}

public class Main {

public static void main(String[] args) {
        CarDealership carDealership = new CarDealership();

Car car_1 = new Car("Toyota Corolla", 26000);
        Car car_2 = new Car("Ford Fiesta", 20000);
        Car car_3 = new Car("Renault Clio", 18000);

carDealership.cars.add(car_1);
        carDealership.cars.add(car_2);
        carDealership.cars.add(car_3);

for (Car car: carDealership.cars) {
            System.out.println("--------");
            car.printData();
        }
    }
}

Output:

Explanation:

At line 23 an ArrayList member is declared.
At line 30 an ArrayList is created.
At lines 43 - 45 elements are added to the ArrayList.
At lines 47 - 50 all elements of the ArrayList are looped.

List

Packages to import

Creation syntax

Example

import java.util.ArrayList;
import java.util.List;

class Student
{
    private String name;
    private int years;

Student(String name, int years)
    {
        this.name = name;
        this.years = years;
    }

public void printData()
    {
        System.out.println("Name: " + this.name);
        System.out.println("Years: " + this.years);
    }
}

class School
{
    public List<Student> students;

School()
    {
        System.out.println("List creation.");

// Create List of students:
        this.students = new ArrayList<Student>();
    }
}

public class Main {

public static void main(String[] args) {
        School school = new School();

Student student_1 = new Student("Emily", 17);
        Student student_2 = new Student("Alex", 18);
        Student student_3 = new Student("John", 16);

school.students.add(student_1);
        school.students.add(student_2);
        school.students.add(student_3);

for (Student student: school.students) {
            System.out.println("--------");
            student.printData();
        }
    }
}

Output:

Explanation:

At line 24 a List member is declared.
At line 31 a List is created.
At lines 44 - 46 elements are added to the List.
At lines 48 - 51 all elements of the List are looped.

ArrayList VS List

Differences:

List

List is an Interface.
List cannot be instantiated.
equals method can be applied (covered in one of the next lessons).

ArrayList

ArrayList is a Class.
ArrayList can be instantiated.
equals method cannot be applied (covered in one of the next lessons).

Similarities:

compareTo method can be applied for both List And ArrayList (covered in one of the next lessons).
Both of them can have dynamic elements count.