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Understanding the 'extends' Keyword in Java

In Java, the 'extends' keyword is used to create a new class that is a modified version of an existing class. This process is known as inheritance. The new class, also known as the subclass or derived class, inherits all the fields and methods of the existing class, also known as the superclass or base class.

Why Use 'extends' in Java?

The 'extends' keyword is used to promote code reusability and facilitate the creation of a hierarchy of related classes. By inheriting the properties and behavior of a superclass, a subclass can build upon the existing functionality and add new features or override the existing ones.

Example of Using 'extends' in Java


// Animal.java (Superclass)
public class Animal {
    private String name;

    public Animal(String name) {
        this.name = name;
    }

    public void eat() {
        System.out.println(name + " is eating.");
    }

    public void sleep() {
        System.out.println(name + " is sleeping.");
    }
}

// Dog.java (Subclass)
public class Dog extends Animal {
    public Dog(String name) {
        super(name);
    }

    public void bark() {
        System.out.println("The dog is barking.");
    }
}

// Main.java
public class Main {
    public static void main(String[] args) {
        Dog myDog = new Dog("Max");
        myDog.eat();  // Output: Max is eating.
        myDog.sleep();  // Output: Max is sleeping.
        myDog.bark();  // Output: The dog is barking.
    }
}

Key Points to Remember

  • A subclass can inherit all the fields and methods of a superclass using the 'extends' keyword.
  • A subclass can add new fields and methods or override the existing ones inherited from the superclass.
  • The 'super' keyword is used to access the members of the superclass from a subclass.
  • A subclass can have its own constructors, but it must call the superclass constructor using the 'super' keyword.

Best Practices for Using 'extends' in Java

When using the 'extends' keyword in Java, follow these best practices:

  • Use inheritance to create a hierarchy of related classes.
  • Avoid deep inheritance hierarchies, as they can lead to tight coupling and make the code harder to maintain.
  • Use the 'super' keyword to access the members of the superclass from a subclass.
  • Override methods in a subclass to provide a specific implementation for the subclass.

Conclusion

In conclusion, the 'extends' keyword in Java is a powerful tool for creating a hierarchy of related classes and promoting code reusability. By understanding how to use 'extends' effectively, you can write more efficient and maintainable code.

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