Abstract class and method in Java

In Java, an abstract class is a class that is declared using the “abstract” keyword, and it cannot be instantiated on its own. Instead, it is used as a base class for other classes to inherit from. An abstract class may contain one or more abstract methods, which are declared without an implementation. Subclasses of an abstract class must provide an implementation for all abstract methods inherited from the parent class, or they must also be declared as abstract classes.

Here’s an example to illustrate the concept of abstract classes and methods:

abstract class Animal {
   public abstract void makeSound();

   public void eat() {
      System.out.println("The animal is eating.");
   }
}

class Cat extends Animal {
   public void makeSound() {
      System.out.println("Meow");
   }
}

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

In the example above, the Animal class is an abstract class that defines an abstract method makeSound() and a non-abstract method eat(). The Cat and Dog classes are subclasses of Animal and they both provide an implementation for the makeSound() method. However, they do not provide an implementation for the eat() method, which is inherited from the Animal class.

Here’s how you can use the Cat and Dog classes:

Animal animal1 = new Cat();
Animal animal2 = new Dog();

animal1.makeSound(); // Output: Meow
animal2.makeSound(); // Output: Woof
animal1.eat(); // Output: The animal is eating.
animal2.eat(); // Output: The animal is eating.

In the example above, we create two instances of the Animal class, one of type Cat and one of type Dog. We call the makeSound() method on both instances, and they each output their respective sound. We also call the eat() method on both instances, and they output the message defined in the Animal class.

Note that it is not possible to create an instance of the Animal class directly, because it is an abstract class. It can only be used as a base class for other classes to inherit from.