In Java, objects and classes are fundamental concepts in object-oriented programming (OOP). Let’s break down each concept:
Overview
- What is Java Object and Classes? Encapsulation and Access Control
- The this Keyword
- Static Members
- Method Overloading
- By Value or By Reference
- Loading, Linking and Initialization
- Comparing Objects
- The Garbage Collector
What Is Java Object & Classes?
- What is Java Object?
- Creating Object
- Java Classes
- Fields
- Methods
- The Method Main
- Constructors
Class
- A class in Java is a blueprint or a template for creating objects. Encapsulation and Access Control
- It defines the properties (fields) and behaviors (methods) that objects of that class will have.
Here’s an example of a simple Java class:
public class Car
{
// Fields (properties)
String make;
String model;
int year;
// Constructor
public Car(String make, String model,
int year)
{
this.make = make;
this.model = model;
this.year = year;
}
// Method
public void startEngine()
{
System.out.println
("The " + year
+ " " + make +
" " + model +
" engine is running.");
}
}
- Remember from the Java Syntax chapter that a class should always start with an uppercase first letter, and that the name of the java file should match the class name.
Object
- An object is an instance of a class. It is a concrete realization of the class blueprint.
- Objects are created from classes using the new keyword and a constructor of the class.
- Each object has its own set of field values, independent of other objects created from the same class.
- You can call the methods of an object to perform actions or interact with its data.
- Here’s how you create and use objects based on the Car class:
public class Main {
public static void main(String[] args)
{
// Creating objects
Car car1 = new Car
("Toyota", "Camry", 2022);
Car car2 = new Car
("Honda", "Civic", 2023);
// Using objects
car1.startEngine();
car2.startEngine();
}
}
In this example, car1 and car2 are objects created from the Car class. They have their own unique values for make, model, and year.
