Chapter 10: Problem 7

How can a subclass method call an overridden superclass method?

Short Answer

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Based on the explanation, describe step by step how a subclass method can call an overridden superclass method. 1. Create a superclass with the required method. For example, we created an "Animal" class with a method called "makeSound". 2. Create a subclass that inherits from the superclass using the "extends" keyword. In our example, we created a "Dog" class that extends the "Animal" class. 3. Override the required method in the subclass. We did this by providing a new implementation of the "makeSound" method in the "Dog" class. 4. Create a new method in the subclass which calls the overridden method from the superclass using the "super" keyword. We created a method called "callSuperclassMakeSound" in the "Dog" class which calls the "makeSound" method from the "Animal" class. 5. Instantiate the subclass and call the new method. The new method will call the original method from the superclass, demonstrating how a subclass method can call an overridden superclass method.

Step by step solution

Creating a superclass

To demonstrate how a subclass method can call an overridden superclass method, we first need to create a superclass. Let's create a simple class named "Animal" representing a generic animal with a method called "makeSound". ```java public class Animal { public void makeSound() { System.out.println("The animal makes a sound"); } } ```

Creating a subclass

Now that we have the superclass, let's create a subclass named "Dog" which inherits from the "Animal" class. To do this, we will use the "extends" keyword in Java. At this point, the "Dog" class will have access to the "makeSound" method of the "Animal" class. ```java public class Dog extends Animal { } ```

Overriding a method in the subclass

Next, we will override the "makeSound" method in the "Dog" class. This will allow the "Dog" class to provide its own implementation of the "makeSound" method, while still having the option to call the original "makeSound" method from the superclass. ```java public class Dog extends Animal { @Override public void makeSound() { System.out.println("The dog barks"); } } ```

Calling the overridden superclass method from the subclass

Finally, let's demonstrate how a subclass method can call an overridden superclass method. In the "Dog" class, we will create a new method called "callSuperclassMakeSound" which will call the overridden "makeSound" method from the "Animal" class. We do this using the "super" keyword in Java. ```java public class Dog extends Animal { @Override public void makeSound() { System.out.println("The dog barks"); } public void callSuperclassMakeSound() { super.makeSound(); } } ``` Now, when we create an instance of the "Dog" class and call its "callSuperclassMakeSound" method, it will call the original "makeSound" method from the superclass "Animal". ```java public class Main { public static void main(String[] args) { Dog dog = new Dog(); dog.callSuperclassMakeSound(); // The animal makes a sound } } ``` This demonstrates how a subclass method can call an overridden superclass method.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Java Inheritance

Inheritance is a fundamental concept in Java, allowing a new class, known as a subclass, to absorb properties and behaviors from an existing class, referred to as a superclass. This mechanism not only fosters code reusability but also establishes a hierarchical relationship between classes.

Think of it as a child inheriting traits from a parent; similarly, the subclass inherits methods and variables from the superclass. The keyword extends is quintessential in declaring this relationship. For instance, in the exercise provided, the Dog class is a subclass that extends the Animal superclass. Consequently, Dog inherits the method makeSound() from Animal, empowering the Dog to either use it as is or modify it to fit more specific needs.

Method Overriding

Method overriding is a powerful Java feature that lets a subclass provide a specific implementation for a method that is already defined in its superclass. This is crucial when the subclass needs to express its unique behavior while maintaining the same method signature.

Through overriding, the subclass can tailor the inherited methods to better reflect its own essence. In the exercise, the Dog class overrides the makeSound() method to bark, representing the dog's specific way of making a sound. Here, the key point is to use the @Override annotation to clarify that the method is overridden and to avoid potential mistakes, like misnaming the method or misaligning the parameters.

Super Keyword in Java

The super keyword in Java holds an essential place in the context of inheritance and method overriding. It is used within a subclass to refer specifically to the superclass portion of an object's memory, allowing direct access to the superclass's methods and fields.

When you override a method but still want to call the version defined in the superclass, super is the tool you reach for. The callSuperclassMakeSound() method in the Dog class exemplifies this usage, leveraging super to invoke the original makeSound() from Animal. It's an acknowledgment that sometimes, the inherited version of a method is precisely what you need, even in an object that has overridden that method to perform a more specialized task.

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How can a subclass method call an overridden superclass method?

Short Answer

Step by step solution

Creating a superclass

Creating a subclass

Overriding a method in the subclass

Calling the overridden superclass method from the subclass

Key Concepts

Java Inheritance

Method Overriding

Super Keyword in Java

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