Abstract Class and Abstract Method in Java

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 In Java, an abstract class is a class that cannot be instantiated directly, and is typically used as a superclass to provide a common interface and behavior to its subclasses. An abstract method is a method that does not have an implementation, and must be implemented by a concrete subclass.

Here are some key characteristics of abstract classes and methods in Java:

  1. Abstract Class:
  • An abstract class is declared using the abstract keyword.
  • An abstract class can have both abstract and non-abstract methods.
  • An abstract class may also have fields, constructors, and non-abstract methods.
  • An abstract class cannot be instantiated directly, but can be used as a reference type for its subclasses.

Here's an example of an abstract class:

java
public abstract class Animal {
    protected int legs;

    public Animal(int legs) {
        this.legs = legs;
    }

    public int getLegs() {
        return legs;
    }

    public abstract void makeSound();
}

In this example, the Animal class is declared as abstract, and has a protected field for the number of legs. It also has a constructor and a non-abstract method for getting the number of legs, as well as an abstract method for making a sound.

  1. Abstract Method:
  • An abstract method is declared using the abstract keyword, and ends with a semicolon instead of a method body.
  • An abstract method must be implemented by any concrete subclass that extends the abstract class that declares the abstract method.

Here's an example of a concrete subclass that extends the Animal class:

java
public class Dog extends Animal {
    public Dog() {
        super(4);
    }

    public void makeSound() {
        System.out.println("Woof!");
    }
}

In this example, the Dog class extends the Animal class, and implements the makeSound method.

In general, abstract classes and methods are used to provide a common interface and behavior for a group of related classes, while allowing for variation in the implementation of that behavior by the concrete subclasses. They can be used to create abstractions and decouple different parts of a program.

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