Question

Write a Line of Code) Write a line of code that performs each of the following tasks: a) Specify that class Pieceworker inherits from class Employee. b) Call superclass Employee's toString method from subclass Pieceworker's toString method. c) Call superclass Employee's constructor from subclass Pieceworker's constructor-assume that the superclass constructor receives three Strings representing the first name, last name and social security number.

Short answer

a) class Pieceworker extends Employee {} b) return super.toString(); c) super(firstName, lastName, socialSecurityNumber);

Step-by-step solution

Inherit From Superclass

To specify that the class 'Pieceworker' inherits from class 'Employee', you will use the extends keyword in the class declaration of 'Pieceworker'.

Call Superclass's toString Method

Inside the 'Pieceworker' class's toString method, use the syntax super.toString() to call the superclass 'Employee's toString method. This is typically done to include the superclass's string representation in the subclass's string representation.

Call Superclass's Constructor

In the 'Pieceworker' class's constructor, use the syntax super(firstName, lastName, socialSecurityNumber) to call the superclass 'Employee's constructor. The parameters passed must match the types expected by the superclass's constructor.

Key concepts

Class Inheritance in Java

In the Java programming language, class inheritance is a fundamental concept that allows a new class, known as a subclass, to inherit properties and methods from an existing class, referred to as a superclass. This mechanism provides a hierarchical classification that not only promotes code reuse but also enhances the manageability of the code.

In the given exercise, declaring that a Pieceworker class inherits from an Employee class is accomplished by using the keyword extends. This creates a subclass-superclass relationship, enabling the Pieceworker to possess all the characteristics of an Employee.

When a class inherits from another, all non-private methods and properties become part of the subclass. However, constructors are not inherited. To handle initialization in the subclass, Java provides a way to call the superclass's constructor, which is crucial for proper object construction.

• Inheritance allows for method overriding, where a method in a subclass can provide its own implementation of a method that it inherited.
• It also leads to a cleaner and more intuitive class structure, where specialized behaviors are separated into subclasses.
• Through inheritance, polymorphism is supported, allowing a single method to work on different kinds of objects.

Superclass Constructor in Java

A superclass constructor is a unique element in Java inheritance that initializes a new object's properties from the superclass. Since constructors are not inherited by the subclass, it is often necessary for the subclass to explicitly call the superclass's constructor, especially if it tends to initialize certain elements that the subclass depends on.

In the context of the exercise, the Pieceworker needs to invoke the constructor of Employee. This is done using the super keyword followed by parentheses enclosing arguments for the superclass constructor. The code super(firstName, lastName, socialSecurityNumber) is written inside the Pieceworker's constructor to ensure that the Employee's state is initialized correctly for the Pieceworker object.

• Using the super keyword guarantees that the inheritance hierarchy is respected and that all necessary initializations in the superclass are performed.
• This mechanism avoids duplication of code and ensures that the superclass's properties are established before the subclass adds or modifies any properties.

Method Overriding in Java

In Java, method overriding occurs when a subclass provides a specific implementation for a method that already exists in its superclass. It is a feature that allows a subclass to tailor the inherited methods to suit its own needs.

In the exercise solution, the Pieceworker class overrides the toString method of the Employee superclass. By calling super.toString() within the overridden toString method, the Pieceworker class can include the string representation of Employee as part of its own string representation.

• Overriding ensures that when a method is invoked on an object of the subclass, the subclass's implementation is executed.
• It is important to ensure that the method signature of the overridden method matches the method signature in the superclass.
• Method overriding is utilized to provide specialized behavior that is different from the general behavior provided by the superclass.

Method overriding is a clear example of polymorphism, where the subclass can define a behavior that's specific to it, while still maintaining the interface defined by the superclass.