Abstract method in java w3schools example

Abstract method in java w3schools example

I'm happy to help you with the abstract method concept in Java!

According to W3Schools (a great online learning platform), an abstract class is a class that cannot be instantiated, and it contains at least one abstract method. Abstract methods are declared without providing any implementation.

Here's an example of an abstract class and its corresponding abstract method:

public abstract class Animal {
public abstract void sound();
}
public class Dog extends Animal {
@Override
public void sound() {
System.out.println("Woof!");
}
}
public class Cat extends Animal {
@Override
public void sound() {
System.out.println("Meow!");
}
}

In this example, Animal is an abstract class that has an abstract method sound(). The Dog and Cat classes are concrete subclasses of Animal, which means they inherit the characteristics (in this case, the abstract method) from their superclass.

The key point here is that the sound() method in Animal does not provide any implementation. Instead, it declares a contract or an interface that needs to be implemented by its subclass (Dog and Cat). This means that when you create an instance of Dog or Cat, you need to override the sound() method with your own implementation.

Here's how you can test this abstract class:

public class Main {
public static void main(String[] args) {
Dog myDog = new Dog();
Cat myCat = new Cat();
myDog.sound(); // Output: Woof!
myCat.sound(); // Output: Meow!
Animal myAnimal = new Animal(); // This is not allowed, because Animal is an abstract class.
}
}

As you can see, when we create instances of Dog and Cat, they are able to override the sound() method with their own implementation. However, trying to instantiate an instance of Animal itself will result in a compile-time error.

In summary, abstract classes and methods allow for polymorphism (the ability of an object to take on different forms) by providing a contract that needs to be implemented by its subclass(es). This concept is essential in Java programming, as it enables more flexibility and reuse of code.

Let me know if you have any questions or need further clarification!

Abstraction example in Java

I'll respond in English this time.

Abstraction is a fundamental concept in object-oriented programming (OOP) that allows developers to create complex systems by breaking them down into smaller, more manageable components. In Java, abstraction is achieved through the use of abstract classes and interfaces.

An abstract class is a class that cannot be instantiated on its own and can only be subclassed. It provides a way to define an interface or a blueprint for other classes to follow. Abstract classes can have both concrete and abstract methods. Concrete methods are fully implemented, while abstract methods are declared but not implemented.

Here's an example of abstraction in Java using an abstract class:

public abstract class Vehicle {
public abstract void start();
public void stop() {
System.out.println("Stopping the vehicle...");
}
}

In this example, Vehicle is an abstract class that has two methods: start() and stop(). The start() method is declared but not implemented, which means it needs to be overridden by any subclass of Vehicle.

Concrete classes can then extend the abstract class and implement the abstract methods. For instance:

public class Car extends Vehicle {
@Override
public void start() {
System.out.println("Starting a car...");
}
}

In this example, Car is a concrete class that extends the Vehicle abstract class. It implements the start() method and provides its own implementation.

Abstraction also allows for polymorphism, which enables objects of different classes to be treated as if they were of the same class. This is achieved through method overriding or overloading.

Here's an example of polymorphism in Java:

public abstract class Shape {
public abstract void draw();
}
public class Circle extends Shape {
@Override
public void draw() {
System.out.println("Drawing a circle...");
}
}
public class Rectangle extends Shape {
@Override
public void draw() {
System.out.println("Drawing a rectangle...");
}
}

In this example, Shape is an abstract class that has one method: draw(). The Circle and Rectangle classes extend the Shape class and provide their own implementations of the draw() method.

Polymorphism allows you to create a collection of shapes without knowing the exact type of each shape:

public class Main {
public static void main(String[] args) {
Shape[] shapes = new Shape[2];
shapes[0] = new Circle();
shapes[1] = new Rectangle();
for (Shape shape : shapes) {
shape.draw();
}
}
}

This code will output:

Drawing a circle...
Drawing a rectangle...

In summary, abstraction in Java allows developers to create complex systems by breaking them down into smaller components. It enables the creation of abstract classes and interfaces that define the structure and behavior of objects without revealing their internal details. Abstraction also enables polymorphism, which allows for the treatment of objects of different classes as if they were of the same class.