Java Ch9
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Java ch9
- 1.
- A.
A subclass is generally larger than its superclass.
- B.
A superclass object is a subclass object.
- C.
The class following the extends keyword in a class declaration is the direct superclass of the class being declared.
- D.
Java uses interfaces to provide the benefits of multiple inheritance.
- 2.Inheritance is also known as the
- A.
“knows-a” relationship.
- B.
“has-a” relationship.
- C.
“uses-a” relationship.
- D.
“is-a” relationship.
- 3.Which of the following is not a superclass/subclass relationship?
- A.
Ford/Taurus.
- B.
University/Brown University
- C.
Sailboat/Tugboat
- D.
Country/USA
- 4.
- A.
All methods can be inherited
- B.
All instance variables can be uniformly accessed by subclasses and superclasses.
- C.
Objects of a subclass can be treated like objects of their superclass.
- D.
None of the above.
- 5.Which of the following keywords allows a subclass to access a superclass method even when the subclass has overridden the superclass method?
- A.
base.
- B.
This
- C.
Public
- D.
Super
- 6.Using the protected keyword gives a member:
- A.
Public access.
- B.
B. package access.
- C.
C. private access.
- D.
D. block scope.
- 7.Superclass methods with this level of access cannot be called from subclasses.
- A.
A. private.
- B.
B. public.
- C.
C. protected.
- D.
D. package.
- 8.Every class in Java, except ________, extends an existing class.
- A.
A. Integer.
- B.
B. Object.
- C.
C. String.
- D.
D. Class.
- 9.Overriding a method differs from overloading a method because:
- A.
A. Overloaded methods have the same signature.
- B.
B. Overridden methods have the same signature.
- C.
C. Both of the above.
- D.
D. Neither of the above.
- 10.9.4.2 Q1: To avoid duplicating code, use ________, rather than ________.
- A.
A. inheritance, the “copy-and-past” approach.
- B.
B. the “copy-and-past” approach, inheritance.
- C.
C. a class that explicitly extends Object, a class that does not extend Object.
- D.
D. a class that does not extend Object, a class that explicitly extends Object.
- 11.
- A.
A. Both variables a and b are instance variables.
- B.
B. After the constructor for class B executes, the variable a will have the value 7.
- C.
C. After the constructor for class B executes, the variable b will have the value 8.
- D.
D. A reference of type A can be treated as a reference of type B.
- 12.9.4.3 Q2: Which of the following is the superclass constructor call syntax?
- A.
A. keyword super, followed by a dot (.) .
- B.
B. keyword super, followed by a set of parentheses containing the superclass constructor arguments.
- C.
C. keyword super, followed by a dot and the superclass constructor name.
- D.
D. None of the above.
- 13.Which superclass members are inherited by all subclasses of that superclass?
- A.
A. private instance variables and methods.
- B.
B. protected instance variables and methods.
- C.
C. private constructors.
- D.
D. protected constructors.
- 14.
- A.
A. A subclass object can assign an invalid value to the superclass’s instance variables, thus leaving an object in an inconsistent state.
- B.
B. Subclass methods are more likely to be written so that they depend on the superclass’s data implementation.
- C.
C. We may need to modify all the subclasses of the superclass if the superclass implementation changes.
- D.
D. All of the above.
- 15.9.4.5 Q1: private fields of a superclass can be accessed in a subclass
- A.
A. by calling private methods declared in the superclass.
- B.
B. by calling public or protected methods declared in the superclass.
- C.
C. directly.
- D.
D. All of the above.
- 16.Failure to prefix the superclass method name with the keyword super and a dot (.) separator when referencing the superclass’s method causes ________.
- A.
A. a compile-time error.
- B.
B. a syntax error.
- C.
C. infinite recursion.
- D.
D. a runtime error.
- 17.9.5 Q1: When a subclass constructor calls its superclass constructor, what happens if the superclass’s constructor does not assign a value to an instance variable?
- A.
A. A syntax error occurs.
- B.
B. A compile-time error occurs.
- C.
C. A run-time error occurs.
- D.
D. The program compiles and runs because the instance variables are initialized to their default values.
- 18.9.6 Q1: Which of the following statements is (are) true?A. We can use inheritance to customize existing software.B. A superclass specifies commonality.C. A superclass can be modified without modifying subclassesD. A subclass can be modified without modifying its superclass.
- A.
A. All of the above.
- B.
B. None of the above.
- C.
C. A, B and C.
- D.
D. A, B and D.
- 19.9.6 Q2: Which of the following is an example of a functionality that should not be “factored out” to a superclass?
- A.
A. Both ducks and geese are birds that know how to start flying from the water.
- B.
B. All vehicles know how to start and stop.
- C.
C. All animals lay eggs, except for mammals.
- D.
D. All paints have a color.
- 20.9.7 Q1: The default implementation of method clone of Object performs a ________.
- A.
A. empty copy.
- B.
B. deep copy.
- C.
C. full copy.
- D.
D. shallow copy.
- 21.9.7 Q2: The default equals implementation determines:
- A.
A. whether two references refer to the same object in memory.
- B.
B. whether two references have the same type.
- C.
C. whether two objects have the same instance variables.
- D.
D. whether two objects have the same instance variable values.
- 22.9.8 Q1: Class ________ represents an image that can be displayed on a JLabel.
- A.
A. Image.
- B.
B. Icon.
- C.
C. ImageIcon.
- D.
D. IconImage.
- 23.9.8 Q2: Which method changes the text the label displays?
- A.
A. changeText.
- B.
B. setText.
- C.
C. changeLabel.
- D.
D. setLabel.
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