How to define an abstract method in java with example

How to define an abstract method in java with example

I'm happy to respond in English for you!

In Java, an abstract method is a method that is declared but not defined in an abstract class. Abstract classes are used when you want to provide a basic implementation of a class, while allowing subclasses to customize and extend the implementation.

To define an abstract method in Java, you need to use the abstract keyword followed by the method signature (return type and parameters). Here's an example:

public abstract class Animal {
public abstract void makeSound();
}

In this example, Animal is an abstract class that declares an abstract method makeSound(). The abstract keyword indicates that this class cannot be instantiated directly, but its subclasses can.

When you declare a method as abstract, you must not provide an implementation for it. If you try to do so, the compiler will throw an error.

Here's an example of a concrete subclass of Animal that implements the makeSound() method:

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

In this example, Dog is a concrete subclass of Animal. It provides an implementation for the makeSound() method by printing "Woof!" to the console.

You can also have multiple abstract methods in an abstract class:

public abstract class Animal {
public abstract void makeSound();
public abstract void eat();
}

In this case, you would need to implement both makeSound() and eat() methods in your concrete subclasses of Animal.

Here's an example of a concrete subclass that implements both abstract methods:

public class Dog extends Animal {
@Override
public void makeSound() {
System.out.println("Woof!");
}
@Override
public void eat() {
System.out.println("Eating kibble...");
}
}

Abstract classes are useful when you want to provide a basic implementation of a class that can be shared by multiple subclasses, but with different behaviors.

In summary, abstract methods in Java allow you to declare a method without providing an implementation. This enables you to define a basic interface for an abstract class, while allowing its concrete subclasses to customize and extend the behavior.

How do you define an abstract variable in Java?

I'm happy to help!

In Java, an abstract variable is a variable that is declared inside an abstract class or interface and has no implementation. Abstract variables are also known as "uninitialized" or "undeclared" variables because they do not have any assigned value.

To declare an abstract variable in Java, you need to use the abstract keyword along with the type of the variable. Here's an example:

public abstract class Animal {
public abstract int age;  // Abstract variable
public void makeSound() {
System.out.println("Animal makes a sound");
}
}

In the above example, age is an abstract variable declared inside the Animal abstract class. It does not have any implementation and needs to be implemented by its subclasses.

Abstract variables are used in Java to provide a way to define a common interface or protocol that must be implemented by all subclasses of an abstract class. This helps in achieving polymorphism, where objects of different classes can be treated as objects of a common superclass.

When you declare an abstract variable, it does not have any default value assigned to it. You need to provide the implementation for this variable in its subclass. Here's an example:

public class Dog extends Animal {
public int age = 3;   // Implementation of the abstract variable
@Override
public void makeSound() {
System.out.println("Dog barks");
}
}

In the above example, age is the implementation of the abstract variable declared in the Animal class. The Dog class provides its own implementation for this variable.

Abstract variables are useful when you need to provide a common interface or protocol that must be implemented by all subclasses of an abstract class. They help in achieving polymorphism and code reuse, making your code more flexible and scalable.

In summary, an abstract variable in Java is a variable that is declared inside an abstract class or interface and has no implementation. It needs to be implemented by its subclasses and provides a way to define a common interface or protocol that must be followed by all subclasses of an abstract class.