FAQ: Object-Oriented Programming

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1 Question 1: How would you define flowchart thinking? Answer 1: Flowcharts are used for describing the steps and functions in a process, equation, or function. The focus is on what happens first, second, third, and so forth. This reflects the mathematical background of its origins. Complex math functions for rocketry and encryption were among the first uses of computer programs. The math functions were diagramed in flowcharts. Later, flowcharts were used to describe entire systems. However, as systems became more and more complex, the use of flowcharts for system description was inadequate because many systems do not operate in the mode of steps. For example, a traffic control system could not be adequately addressed by a flowchart because there is no one starting and ending point. Neither could database management be addressed by a flowchart because it has many different functions and must deal with many users concurrently. Question 2: Are flowcharts useful anywhere in object-oriented programming today? Answer 2: Flowchart diagrams are helpful when used for their original purpose that is, to diagram a limited piece of functionality in an object-oriented program. For example, if such a program has a function that goes through steps for operating a piece of equipment or reading and processing operations in a database, then a flowchart would be a good choice for a diagram method. For example, there is a function called Ride Elevator. There could be flowchart steps that say these: 1. User presses the elevator button at the user's floor. 2. If elevator is on the floor, then open the door. 3. Move the elevator to the floor where the person is, and then open the door. 4. User walks into elevator. 1

2 5. User selects destination floor. 6. Elevator moves to destination floor. 7. Door opens. 8. User exits elevator. 9. Door closes. 10. Elevator goes idle. Question 3: Why did the industry move away from using structured design toward object-oriented design? Answer 3: Structured design was the process used in the 1970s and 1980s in design software before object-oriented design. Structured design would take a problem and break it down into smaller, simpler problems before coding would begin. Structured design did not have programming languages to support it. Therefore, the programs could become highly disorganized. Code in one function could impact data that are used by another function. The programming languages at the time (1950s to early 1990s) used global variables and passed information from one subsystem to another. The resulting programs were often impossible to maintain and debug, resulting in cost overruns and reliability problems. Question 4: What approach does an object-oriented program designer take toward solving a problem? Answer 4: An object-oriented program designer or software architect looks at a problem by first asking, "What are the objects in the software system that I must first discover?" Each object will have data that it manages and will have behaviors ascribed to it. Notice that the software architect does not think about what happens first in the system, nor does the architect look at breaking down the system from complex problems to smaller and smaller problems as was done in the past. Rather, the software architect thinks about the objects in the system. 2

3 Objects can be real-world concepts like people, places, or things. Objects can also be computer concepts like databases. Question 5: Describe the objects managed by a playing card object for a computer game of Solitaire. Answer 5: Objects in an object-oriented programming language are often real-world objects like playing cards, for example. Objects can contain other objects. For example, a playing card object will have a front cover and a back cover. Objects in a programming language must be managed by the computer and must perform functions known as behaviors. Consider further the playing card object: The playing card object has the following objects associated with it: Back cover object with attributes: pattern and texture Front cover object with attributes: texture, card suit, card ID (e.g, 2 10, J, Q, K, A, Joker) When the card is displayed on the computer screen, it will need functions (behaviors) such as these: Draw back cover: This takes the pattern and texture attributes and draws the back cover on the screen when the Solitaire game commands it to do so. Draw front cover: This takes the texture, card suit, and card ID and draws the front cover of the card on the screen when the Solitaire game commands it to do so. Question 6: What is meant by object reuse in object-oriented programming? Answer 6: The term object reuse means that software objects can be included in an infinite number of new programs. For example, in Java, there is a String 3

4 object. Every time a line of text must be stored, a new String object is created to store that specific line of text. Each String object in all Java programs is identical in its structure and its behavior. The only thing different between the manufactured String objects is the actual text that they store. This is analogous to a gasoline tank on a car. Identical models of a certain car will have identical gasoline tanks. The only thing different between the identical gasoline tanks will be the amount of gasoline in them. Question 7: What are the characteristics of reusable objects? Answer 7: Consider the parts of a wooden chair. The spindles, backs, legs, and seats of a wooden chair are all manufactured with specific interfaces so that they can be quickly assembled into complete wooden chairs. The diameter of the holes must exactly match the spindles or legs (a special kind of spindle) that fit into them. To be reusable, software objects must also have well-defined interfaces so that one object knows how to communicate with another object. For example, in an airplane control program, the Wing object must be able to communicate with a Fuel control object so that an Engine object can receive fuel. Welldefined, rigid interfaces are essential so that the software objects fit together like the parts of a chair do. Question 8: How does an object-oriented language like Java support an object-oriented design? Answer 8: Java and other object-oriented programming languages define objects with the statements of the object-oriented language known as program code. Objects are manufactured by Java programs off of object templates called classes. 4

5 For example: Person objects are created in a Java program according to the Person class: class Person{ String name; //John Doe String address; //200 Some Street String getname() { return name; } String getaddress {return address;} } Every Person object that is created by the Java program will have a string of characters to hold the name, a string of characters to hold the address, and a function that allows the Java program to retrieve a person's name and address by providing the getname() method and getaddress() methods. A class therefore is a blueprint for an object. A class does not actually have any data nor execute any code, just like the blueprint for a house is not actually a house. The Java program uses the class definition to create an object in memory. It is the object that actually executes code and manages data. Question 9: What is encapsulation of objects? Answer 9: Encapsulation of an object means that one object hides its data from another object and the only way one object can affect the data in another object is through the other objects interfaces (also called methods or operations). For example, the Wing object in an airplane program knows nothing about the Engine object other than where to send the fuel. It does not know if the engine is a jet or a propeller engine. It does not need to know. All it knows is that it needs to send the right amount of fuel to the engine. Question 10: Name at least 10 real-world objects present in a car race simulation program. 5

6 Answer 10: Object-oriented programs contain objects that can represent real-world objects such as persons, places, and things. For example, an Employee Database program would track employee information inside of the database. Computer games have objects like weapons and fighter jets. Examples are the following: Racing cars (considering many objects in a racing car, such as wheels, fuel gauges, seats, etc.) Race track Driver Mechanics Judges Spectators Flags Advertisements Speakers 6