Adding properties

Introduction to Object-Oriented Programming in Java

Sani Yusuf

Lead Software Engineering Content Developer

Car example

Cars on the road can come in different forms, with features like color and model that differentiate them.

Cars

Differentiate cars

Even when cars are the same, they differ by color, license plate, vehicle registration.

Same Cars

Adding properties to class

Properties describe a class
Properties can have different data types


  // Car class
  class Car {
    String model; // Property for model of car

    int topSpeed; // Property for car's top speed
    boolean isInsured; // Property for current insurance state
  }

Constructors in Java

The Constructor is a method, always called when an object instance of a class is created
Constructor must have the same name as the class it is in


  class Passport {
    String firstName; // Passport holder's first name
    String lastName; // Passport holder's last name

    Passport() {
      // Constructor of Passport class
    }
  }

Setting properties inside the constructors


  class Passport {
    String firstName; // Passport holder's first name
    String lastName; // Passport holder's last name

    Passport() {
      this.firstName = "David";  // Set property inside constructor
      this.lastName = "Beckham";
    }
  }

Constructors with parameters

Constructors can have parameters just like any other method


  class Passport {
    String firstName;
    String lastName;

    // Constructor with parameters
    Passport(String firstName, String lastName) {  

    }
  }

Setting properties with constructor parameters

The this keyword refers to the Passport object
It is common to give constructor parameters same name as class properties


  class Passport {
    String firstName;
    String lastName;

    Passport(String firstName, String lastName) {
          this.firstName = firstName; // Setting class properties
          this.lastName = lastName;   //  with constructor parameters
    }
  }

Creating object instances with parameters

Objects are created with the new keyword
Constructor parameters are passed during object creation


  // Passport Class with constructor
  class Passport {
    String firstName;
    String lastName;

    // Constructor method
    Passport(String firstName, 
             String lastName){
          this.firstName = firstName;
          this.lastName = lastName;
    }
  }


  // Main Class    
  public class Main {  
    // main method (program entry point)
    public static void main(
      String[] args) {

      // Passing parameters to constructor 
      // Passport(firstName, lastName)
      Passport myPassport = 
        new Passport("Michael","Jackson"); 
      System.out.println(
        myPassport.firstName); // Michael
    }
  }

Let's practice!

Introduction to Object-Oriented Programming in Java