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Exam 9: Inheritance

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Question 31

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For the questions below, use the following partial class definitions: public class A1 { public int x; private int y; protected int z; ... } public class A2 extends A1 { protected int a; private int b; ... } public class A3 extends A2 { private int q; ... } -Which of the following is True regarding the use of instance data y of class A1?

A) It is accessible in A1, A2 and A3
B) It is accessible in A1 and A2
C) It is accessible only in A1
D) It is accessible only in A3
E) It is not accessible to any of the three classes

F) A) and B)
G) B) and C)

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Question 32

Multiple Choice

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What is the advantage of using an Adapter class?

A) It relieves the programmer from having to declare required methods with empty bodies
B) It is more efficient at run time
C) It relieves the programmer from having to shadow the required Interface variables
D) It allows a programmer to be more explicit about exactly which methods are being overridden and in what manner
E) none of the above

F) C) and D)
G) None of the above

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Question 33

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A derived class has access to all of the methods of the parent class, but only the protected or public instance data of the parent class.

If a class extends Applet and also implements MouseListener and MouseMotionListener, what methods must be declared in this class?

For the questions below, assume that Student, Employee and Retired are all extended classes of Person, and all four classes have different implementations of the method getMoney. Consider the following code where ... are the required parameters for the constructors: Person p = new Person(...) ; int m1 = p.getMoney( ) ; // assignment 1 p = new Student(...) ; int m2 = p.getMoney( ) ; // assignment 2 if (m2 < 100000) p = new Employee(...) ; else if (m1 > 50000) p = new Retired(...) ; int m3 = p.getMoney( ) ; // assignment 3 -The reference to getMoney( ) in assignment 2 is to the class

Which of these is correct?

An applet implements MouseListener, and has int instance data x and y. These variables will be the (X, Y) coordinates of where the mouse is clicked. Every time the mouse is clicked, draw a 40x40 Oval centered around x and y. Write the mouseClicked and paint methods to draw the Oval every time the mouse is clicked.

A motorcycle inherits properties from both a bicycle and a car. Java does not permit multiple inheritance. Assume that Bicycle and Car have both been declared. Explain how you might go about implementing a Motorcycle as a derived class.

A mouse event is a(n)

Which of the following is an example of multiple inheritance?

Consider a class Name, which has four instance data (all Strings): first, middle, last and title. Even though Name inherits the equal method from Object, it would make more sense to override it. Why?

For the questions below, consider the following class definition: public class AClass { protected int x; protected int y; public AClass(int a, int b) { x = a; y = b; } public int addEm( ) { return x + y; } public void changeEm( ) { x++; y--; } public String toString( ) { return "" + x + " " + y; } } -Which of the following would best redefine the toString method for BClass?

Which of the following is not a method of the Object class?

Interface classes cannot be extended but classes that implement interfaces can be extended.

In what manners are Timer objects similar to and different from other GUI components?

Assume a class Triangle has been defined. It has three instance data, Point p1, p2, p3. The class also has a constructor that receives the 3 Points and initializes p1, p2, and p3, a toString method that outputs the 3 Points, and a computeSurfaceArea method that calculates the surface area of the Triangle (as an int value). We want to extend this class to represent a 3-dimensional Pyramid, which consists of 4 Points. Since the Pyramid will consist of in essence, 4 triangles, computeSurfaceArea for the Pyramid will compute 4 * the surface area of the Triangle made up of 3 of those 4 Points. Write the Pyramid class to handle the difference(s) between a Pyramid and the previously defined Triangle. Assume the instance data of Triangle are protected and all methods are public. Also assume that the class Point has a toString method.

For the questions below, assume that Student, Employee and Retired are all extended classes of Person, and all four classes have different implementations of the method getMoney. Consider the following code where ... are the required parameters for the constructors: Person p = new Person(...) ; int m1 = p.getMoney( ) ; // assignment 1 p = new Student(...) ; int m2 = p.getMoney( ) ; // assignment 2 if (m2 < 100000) p = new Employee(...) ; else if (m1 > 50000) p = new Retired(...) ; int m3 = p.getMoney( ) ; // assignment 3 -The relationship between a parent class and a child class is referred to as a(n) ________ relationship.

Consider the following class hierarchy and answer these questions. -Y is a derived class of Z.

Inheritance through an extended (derived) class supports which of the following concepts?

In order to implement the MouseListener interface, the programmer must define all of the following methods except for