super keyword in Java : Complete Guide

This extensive guide aims to explore and uncover the diverse capabilities and importance of the super keyword in Java. It provides valuable insights into its usage and recommended practices, helping developers fully grasp its potential and leverage it effectively in their code.

What is super keyword in Java?

The super keyword in Java is a reference variable that is used to refer to the superclass or parent class of a subclass.

Usage of super keyword

The super keyword in Java has several important uses and plays a significant role in object-oriented programming. Here are the key uses of the super keyword in Java:

1. Accessing Superclass Members.
2. Invoking Superclass Constructors.
3. Differentiating Between Superclass and Subclass Members.
4. Accessing Superclass Implementation.
5. Navigating Through Inheritance Hierarchies.

Accessing Superclass Members

The super keyword in Java is used to access members (variables and methods) of the superclass from within a subclass. This allows the subclass to utilize and extend the functionality defined in the superclass.

Here’s an example Java code snippet to demonstrate accessing superclass members using the “super” keyword:

class Animal {
    protected String name;

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

    public void makeSound() {
        System.out.println("Animal is making a sound");
    }
}

class Dog extends Animal {
    private int age;

    public Dog(String name, int age) {
        super(name); // Invoking the superclass constructor using "super"
        this.age = age;
    }

    @Override
    public void makeSound() {
        super.makeSound(); // Invoking the superclass method using "super"
        System.out.println("Dog is barking");
    }

    public void displayInfo() {
        System.out.println("Name: " + super.name); // Accessing the superclass variable using "super"
        System.out.println("Age: " + age);
    }
}

public class Main {
    public static void main(String[] args) {
        Dog dog = new Dog("Buddy", 3);
        dog.makeSound(); // Output: Animal is making a sound\nDog is barking
        dog.displayInfo(); // Output: Name: Buddy\nAge: 3
    }
}

In the above example:

• The Animal class has a protected name variable and a makeSound() method.
• The Dog class extends Animal and adds an age variable.
• In the Dog constructor, super(name) is used to invoke the superclass constructor and initialize the name variable.
• The makeSound() method in the Dog class overrides the superclass method and utilizes super.makeSound() to invoke the superclass implementation.
• The displayInfo() method in the Dog class accesses the superclass variable name using super.name.
• In the Main class, an instance of Dog is created and various methods are called to demonstrate accessing superclass members using the “super” keyword.

By using “super” in the appropriate contexts, you can effectively access and utilize superclass members within a subclass, allowing for code reuse and customization.

Invoking Superclass Constructors

The super keyword in Java is used to invoke the constructors of the superclass from within a subclass. This allows the subclass to inherit and initialize the state of the superclass before performing its own specific initialization.

Here’s an example Java code snippet to demonstrate invoking superclass constructors using the “super” keyword:

class Animal {
    protected String name;

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

class Dog extends Animal {
    private int age;

    public Dog(String name, int age) {
        super(name); // Invoking the superclass constructor using "super"
        this.age = age;
    }

    // Other methods and members
}

public class Main {
    public static void main(String[] args) {
        Dog dog = new Dog("Buddy", 3);
        // Other operations with the Dog instance
    }
}

In the above example:

• The Animal class has a parameterized constructor that takes a name argument.
• The Dog class extends Animal and adds an age variable.
• In the Dog constructor, super(name) is used to invoke the superclass constructor and initialize the name variable.
• The age variable is initialized in the Dog constructor itself.
• In the Main class, an instance of Dog is created, invoking the superclass constructor through the subclass constructor using the “super” keyword.

Differentiating Between Superclass and Subclass Members

In Java, when a subclass extends a superclass, it is possible to have members (variables and methods) with the same name in both the superclass and subclass. To differentiate between these members and specify which one to use, the super keyword can be used.

Here’s an example code snippet to demonstrate differentiating between superclass and subclass members using the super keyword in Java:

class Animal {
    protected String name = "Animal";

    public void printName() {
        System.out.println("Name: " + name);
    }
}

class Dog extends Animal {
    protected String name = "Dog";

    @Override
    public void printName() {
        System.out.println("Subclass Name: " + name);
        System.out.println("Superclass Name: " + super.name); // Accessing superclass variable using "super"
    }
}

public class Main {
    public static void main(String[] args) {
        Dog dog = new Dog();
        dog.printName();
    }
}

In the above example:

• The Animal class has a protected variable name and a printName() method.
• The Dog class extends Animal and has its own protected variable name.
• The printName() method in the Dog class overrides the superclass method and differentiates between the subclass and superclass variables using the “super” keyword.

When the printName() method is called, the subclass Dog differentiates between its own name variable and the superclass name variable by using super.name to access the superclass variable directly.

Accessing Superclass Implementation

In Java, when a subclass overrides a method from its superclass, it is sometimes necessary to access the implementation of the overridden method in the superclass. The “super” keyword allows you to explicitly invoke the superclass implementation of a method from within the subclass.

Here’s an example Java code snippet to demonstrate accessing superclass implementation using the “super” keyword:

class Animal {
    public void makeSound() {
        System.out.println("Animal is making a sound");
    }
}

class Dog extends Animal {
    @Override
    public void makeSound() {
        super.makeSound(); // Invoking the superclass implementation using "super"
        System.out.println("Dog is barking");
    }
}

public class Main {
    public static void main(String[] args) {
        Dog dog = new Dog();
        dog.makeSound();
    }
}

In the above example:

• The Animal class has a method makeSound() that prints a generic sound message.
• The Dog class extends Animal and overrides the makeSound() method.
• Inside the overridden method, super.makeSound() is used to invoke the superclass implementation before printing the specific bark message.

When the makeSound() method is called on the Dog instance, it first invokes the superclass implementation using super.makeSound(), which prints “Animal is making a sound”. Then, it proceeds to execute the subclass-specific code, printing “Dog is barking”.

Navigating Through Inheritance Hierarchies

In Java, when dealing with complex inheritance hierarchies or multilevel inheritance, it may be necessary to access members (variables and methods) defined in higher-level superclasses. The super keyword in Java facilitates navigation through the inheritance chain, allowing you to access members from distant superclasses.

Here’s an example Java code snippet to demonstrate navigating through inheritance hierarchies using the “super” keyword:

class Animal {
    public void eat() {
        System.out.println("Animal is eating");
    }
}

class Mammal extends Animal {
    public void run() {
        System.out.println("Mammal is running");
    }
}

class Dog extends Mammal {
    public void bark() {
        System.out.println("Dog is barking");
    }

    public void dogAction() {
        super.eat(); // Accessing the eat() method from the Animal class using "super"
        super.run(); // Accessing the run() method from the Mammal class using "super"
        bark();
    }
}

public class Main {
    public static void main(String[] args) {
        Dog dog = new Dog();
        dog.dogAction();
    }
}

In the above example:

• The Animal class has an eat() method.
• The Mammal class extends Animal and adds a run() method.
• The Dog class extends Mammal and adds a bark() method and a dogAction() method that demonstrates navigating through the inheritance chain using the “super” keyword.

In the dogAction() method, super.eat() accesses the eat() method defined in the Animal class, and super.run() accesses the run() method defined in the Mammal class. Finally, bark() is called directly in the Dog class.

Recommended practices for using super keyword in Java

When using the super keyword in Java, it’s important to follow recommended practices to ensure clean and maintainable code. Here are the key practices to consider:

1. It’s important to use the “super” keyword explicitly when accessing superclass members or invoking superclass constructors.
2. When invoking a superclass constructor using “super”, ensure that it is the first statement in the subclass constructor.
3. use the super keyword in Java judiciously and only when necessary.
4. When overriding a method in the subclass, carefully consider whether you need to invoke the superclass implementation using “super”.
5. Adhere to consistent naming conventions for variables and methods in both the superclass and subclass to prevent naming conflicts.
6. When using the “super” keyword, it can be helpful to provide comments or documentation explaining your intentions.
7. Ensure that your team or project follows consistent coding practices when using the super keyword in Java.

Conclusion

In conclusion, the super keyword in Java is a powerful tool that allows for accessing and invoking members of the superclass, resolving naming conflicts, navigating through inheritance hierarchies, and enhancing code flexibility. By following recommended practices such as using “super” explicitly, invoking superclass constructors first, avoiding excessive usage, overriding methods carefully, following naming conventions, documenting intentions, and maintaining consistency, you can ensure clean and maintainable code.