How to Use a Superclass to Initialize a Subclass Object in Java?

How can I use a superclass to initialize a subclass object in Java?

class Superclass {
    void display() {
        System.out.println("This is a superclass method.");
    }
}

class Subclass extends Superclass {
    void display() {
        System.out.println("This is a subclass method.");
    }
}

public class Main {
    public static void main(String[] args) {
        Superclass obj = new Subclass();
        obj.display(); // Calls the subclass method
    }
}

In Java, initializing a subclass object using a superclass reference is a common practice that allows for polymorphism, enabling method overriding and dynamic method dispatch.

class Animal {
    void sound() {
        System.out.println("Animal makes a sound.");
    }
}

class Dog extends Animal {
    void sound() {
        System.out.println("Dog barks.");
    }
}

class Cat extends Animal {
    void sound() {
        System.out.println("Cat meows.");
    }
}

public class Main {
    public static void main(String[] args) {
        Animal myDog = new Dog();
        Animal myCat = new Cat();
        myDog.sound(); // Outputs: Dog barks.
        myCat.sound(); // Outputs: Cat meows.
    }
}

Causes

• Understanding inheritance in Java
• Need for polymorphic behavior in applications
• Desire to treat objects of different classes similarly

Solutions

• Use a superclass type reference to hold a subclass object.
• Override methods in the subclass to provide specific implementations.
• Call the overridden methods using the superclass reference.

Mistake: Confusing the superclass and subclass references

Solution: Always ensure that you use the correct reference type to avoid compilation errors.

Mistake: Failing to override methods in the subclass

Solution: Make sure to implement the overridden methods in the subclass to achieve polymorphic behavior.