To test our Employee hierarchy, the application in Figure Class SalariedEmployee’s constructor passes the first name, last name and social security number to the Employee constructor line 12 to initialize the private instance variables not inherited from the superclass. Software Engineering Observation For example, line 46 implicitly invokes method toString of the object to which currentEmployee refers. To do so, you can modify class Employee Fig. As you’ll soon see, when we invoke each employee’s earnings method off a superclass Employee reference, the correct earnings calculation is performed due to Java’s polymorphic capabilities. We explore GUI programming in Chapters 14 and
Be sure to include private reference-type attributes based on class Transaction’s associations. Be careful not to confuse the general notion of an “interface” to something with the formal notion of a Java interface, the subject of Section As a result of dynamic binding, Java decides which class’s toString method to call at execution time rather than at compile time. Lines 9—18 create objects of each of the four concrete Employee subclasses. Should we wish to create a new transaction type e.
However, these operators cannot be used to compare the contents of objects.
Chapter Object-Oriented Programming: Polymorphism – CodeProject
The following sections implement the Employee class hierarchy of Fig. Software Engineering Observation If we do not implement earnings, class SalariedEmployee must be declared abstract—otherwise, a compilation error occurs and, of course, we want SalariedEmployee here to be a concrete class.
For each device, the operating system uses a piece of soft- ware called a device driver to control all communication between the system and the de- vice. It simply does not make sense to provide an implementation of this method in class Employee.
Java™ How To Program (Early Objects), Tenth Edition by Harvey Deitel, Paul Deitel
Each TwoDimen- sionalShape should contain method getArea to calculate the area of the two-dimensional shape. The UML class diagram in Figure Line 37 assigns the reference to an HourlyEmployee object to employees[ 1 ].
We create an enhanced employee hierarchy to solve the following problem: First, we discuss common examples of polymorphism.
Line 9 de- clares payableObjects and assigns it an array of four Payable variables. Hierarchies designed for interface inheritance tend to have their functionality lower in the hierarchy—a superclass specifies one or more abstract methods that must be declared for each concrete class in the hierarchy, and the individual subclasses override these methods to provide subclass-specific implementations.
Chapter 10: Object-Oriented Programming: Polymorphism
However, the write call itself really is no different from the write to any other device in the system: In addition, method toString calls superclass method toString line 56 to obtain the Employee -specific information i.
Self-Review Exercises Section Although a subclass object also is a superclass object, the two objects are nevertheless different. Relying on each object to know how to “do the right thing” i. All methods of class Object can be called by using a reference of an interface type.
When fully implemented, methods getScreen and getBankDatabase will patroll superclass Transaction’s private reference attributes screen and bankDatabase, respectively.
(PDF) Chapter 10 Object Oriented Programming | Yucheng Liao –
The UML class diagram in Fig. Lines then assign the polymirphism to subclass object basePlusCommissionEmployee to a superclass CommissionEmployee3 variable, which lines use to invoke method toString.
The next example introduces an interface named Payable to describe the functionality of any object that must be capable of being paid and thus must offer a method polymrophism determine the proper payment amount due. The hierarchy begins with interface Payable. We recommend that you carefully read the code and its description. To apply inheritance, we first look for commonality among classes in the system.
Let us consider class Employee’s declaration Figure These assignments are natural—for example, a CommissionEmployee3 variable’s primary purpose is to hold a reference to a CommissionEmployee3 object. Occasionally, when performing polymorphic processing, we need to program “in the specific. Note that method execute is not italicized in subclasses BalanceInquiry, Withdrawal caae Deposit.
Deitel Jun 1, We explore GUI programming in Chapters 14 and Similarly, the interface between a syste, and a car with a manual transmission includes the steering wheel, the gear shift, the clutch pedal, the gas pedal and the brake pedal. We use abstract class Employee to represent the general concept of an uslng. Line 38 assigns the reference to a CommissionEmployee object to employees[ 2 ]. In the current section and in Section