**Course Title:** Comprehensive Java Programming: From Basics to Advanced Concepts **Section Title:** Inheritance and Polymorphism in Java **Topic:** The 'super' keyword and chaining constructors. In the previous topic, we covered method overriding and runtime polymorphism in Java. Now, we'll explore the 'super' keyword and chaining constructors in the context of inheritance. **What is the 'super' keyword?** In Java, the 'super' keyword is used to access the members of a superclass from a subclass. The 'super' keyword can be used in the following scenarios: 1. **Invoking the superclass constructor**: The 'super' keyword can be used to invoke the constructor of the superclass from the subclass constructor. 2. **Accessing superclass members**: The 'super' keyword can be used to access the methods and variables of the superclass from the subclass. **Example 1: Invoking the superclass constructor using 'super'** ```java // Animal.java (superclass) public class Animal { public Animal() { System.out.println("Animal constructor"); } } // Dog.java (subclass) public class Dog extends Animal { public Dog() { super(); // invoking the superclass constructor System.out.println("Dog constructor"); } public static void main(String[] args) { Dog dog = new Dog(); } } ``` In the above example, when we create a new instance of the `Dog` class, the `Dog` constructor is called, which in turn invokes the `Animal` constructor using the `super()` method. The output will be: ``` Animal constructor Dog constructor ``` **Example 2: Accessing superclass members using 'super'** ```java // Animal.java (superclass) public class Animal { public void sound() { System.out.println("The animal makes a sound"); } } // Dog.java (subclass) public class Dog extends Animal { public void sound() { super.sound(); // accessing the superclass method System.out.println("The dog barks"); } public static void main(String[] args) { Dog dog = new Dog(); dog.sound(); } } ``` In the above example, the `Dog` class overrides the `sound()` method of the `Animal` class. Inside the `sound()` method of the `Dog` class, we use the `super` keyword to access the `sound()` method of the `Animal` class. The output will be: ``` The animal makes a sound The dog barks ``` **Chaining Constructors** Constructor chaining is a technique where one constructor calls another constructor of the same class or its superclass. This is done using the `this()` or `super()` keyword. **Example 3: Constructor chaining in the same class** ```java // Employee.java public class Employee { private String name; public Employee() { this("John Doe"); // calling another constructor of the same class } public Employee(String name) { this.name = name; } public static void main(String[] args) { Employee employee = new Employee(); } } ``` In the above example, the no-arg constructor calls the constructor with a parameter using the `this()` method. **Example 4: Constructor chaining to the superclass** ```java // Manager.java (subclass) public class Manager extends Employee { public Manager() { super("John Doe"); // calling the superclass constructor System.out.println("Manager constructor"); } public static void main(String[] args) { Manager manager = new Manager(); } } ``` In the above example, the `Manager` class constructor calls the `Employee` class constructor using the `super()` method. **Best Practices** * Always use the `super` keyword to access the members of the superclass. * Use constructor chaining to reduce code duplication and improve readability. **Conclusion** In this topic, we covered the 'super' keyword and constructor chaining in Java. We saw how to use the 'super' keyword to access the members of the superclass and how to use constructor chaining to reduce code duplication. **What's Next?** In the next topic, we'll cover the benefits and limitations of inheritance in Java. Please provide feedback and ask questions in the comments section below. **External Resources:** * Oracle Java Documentation: [Using the Keyword super](https://docs.oracle.com/javase/tutorial/java/IandI/super.html) * Stack Overflow: [How does the 'super' keyword work in Java?](https://stackoverflow.com/questions/376736/how-does-the-super-keyword-work-in-java) **Leave a comment/ask for help:** Please leave a comment or ask for help if you have any questions or need further clarification on the concepts covered in this topic.