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Exam 9: Inheritance

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Question 1

Multiple Choice

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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?

A) public String toString(int z) {
Return " " + x + " " + y + " " + z;
}
B) public String toString( ) {
Return super.toString( ) ;
}
C) public String toString( ) {
Return super.toString( ) + " " + z;
}
D) public String toString( ) {
Return super.toString( ) + " " x + " " + y + " " + z;
}
E) public String toString( ) {
Return " " + x + " + y + " " + z;
}

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

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Question 2

Multiple Choice

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For the next questions, consider the following class definition: public class Q { private int x; public Q(int newValue) { x = newValue; } } -Which of the following is True about the class Q26_27?

A) It has no parent class
B) Its parent class is Object
C) Its parent class is Java
D) It can not be extended
E) It has a default child called Object

F) C) and D)
G) B) and E)

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Question 3

True/False

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Regarding the Software Failure: Mid-air collisions were avoided in the 2004 LA Air Traffic Control incident due to the on-board collision avoidance systems now found on commercial jets.

Explain the difference between using an imported class and extending a class.

All classes in Java are directly or indirectly subclasses of the ________ class.

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.

Which of the following is True regarding the use of instance data y of class A1?

If a programmer writes a class wanting it to be extended by another programmer, then this programmer must

For the questions below, assume that Poodle is a derived class of Dog and that Dog d = new Dog(...) and Poodle p = new Poodle(...) where the ... are the necessary parameters for the two classes. -The assignment statement d = p; is legal even though d is not a Poodle.

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

JApplet is an extension of the Applet class and is found in the ________ library.

A mouse event is a(n)

Which of the following is an example of multiple inheritance?

Why shouldn't an abstract method be declared final?

The protected visibility modifier provides the best possible encapsulation that permits inheritance.

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.

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.

A variable declared to be of one class can later reference an extended class of that class. This variable is known as

Consider the following class hierarchy and answer these questions. -A is a derived class of X.

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 with respect to A1, A2 and A3?