23 Questions | Total Attempts: 1545
-
Which of the following statements is false?
-
A subclass is generally larger than its superclass.
-
A superclass object is a subclass object.
-
The class following the extends keyword in a class declaration is the direct superclass of the class being declared.
-
Java uses interfaces to provide the benefits of multiple inheritance.
-
-
Inheritance is also known as the
-
Which of the following is not a superclass/subclass relationship?
-
University/Brown University
-
: An advantage of inheritance is that:
-
All methods can be inherited
-
All instance variables can be uniformly accessed by subclasses and superclasses.
-
Objects of a subclass can be treated like objects of their superclass.
-
-
Which of the following keywords allows a subclass to access a superclass method even when the subclass has overridden the superclass method?
-
Using the protected keyword gives a member:
-
Superclass methods with this level of access cannot be called from subclasses.
-
Every class in Java, except ________, extends an existing class.
-
Overriding a method differs from overloading a method because:
-
A. Overloaded methods have the same signature.
-
B. Overridden methods have the same signature.
-
-
9.4.2 Q1: To avoid duplicating code, use ________, rather than ________.
-
A. inheritance, the “copy-and-past” approach.
-
B. the “copy-and-past” approach, inheritance.
-
C. a class that explicitly extends Object, a class that does not extend Object.
-
D. a class that does not extend Object, a class that explicitly extends Object.
-
-
Consider the classes below, declared in the same file:class A { int a; public A() { a = 7; }}class B extends A { int b; public B() {b = 8; } }Which of the statements below is false?
-
A. Both variables a and b are instance variables.
-
B. After the constructor for class B executes, the variable a will have the value 7.
-
C. After the constructor for class B executes, the variable b will have the value 8.
-
D. A reference of type A can be treated as a reference of type B.
-
-
9.4.3 Q2: Which of the following is the superclass constructor call syntax?
-
A. keyword super, followed by a dot (.) .
-
B. keyword super, followed by a set of parentheses containing the superclass constructor arguments.
-
C. keyword super, followed by a dot and the superclass constructor name.
-
-
Which superclass members are inherited by all subclasses of that superclass?
-
A. private instance variables and methods.
-
B. protected instance variables and methods.
-
D. protected constructors.
-
-
9.4.4 Q2: Which statement is true when a superclass has protected instance variables?
-
A. A subclass object can assign an invalid value to the superclass’s instance variables, thus leaving an object in an inconsistent state.
-
B. Subclass methods are more likely to be written so that they depend on the superclass’s data implementation.
-
C. We may need to modify all the subclasses of the superclass if the superclass implementation changes.
-
-
9.4.5 Q1: private fields of a superclass can be accessed in a subclass
-
A. by calling private methods declared in the superclass.
-
B. by calling public or protected methods declared in the superclass.
-
-
Failure to prefix the superclass method name with the keyword super and a dot (.) separator when referencing the superclass’s method causes ________.
-
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 syntax error occurs.
-
B. A compile-time error occurs.
-
C. A run-time error occurs.
-
D. The program compiles and runs because the instance variables are initialized to their default values.
-
-
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.
-
9.6 Q2: Which of the following is an example of a functionality that should not be “factored out” to a superclass?
-
A. Both ducks and geese are birds that know how to start flying from the water.
-
B. All vehicles know how to start and stop.
-
C. All animals lay eggs, except for mammals.
-
D. All paints have a color.
-
-
9.7 Q1: The default implementation of method clone of Object performs a ________.
-
9.7 Q2: The default equals implementation determines:
-
A. whether two references refer to the same object in memory.
-
B. whether two references have the same type.
-
C. whether two objects have the same instance variables.
-
D. whether two objects have the same instance variable values.
-
-
9.8 Q1: Class ________ represents an image that can be displayed on a JLabel.
-
9.8 Q2: Which method changes the text the label displays?
- HTML
- Server
- PHP
- Computer Science
- SQL
Given:
public class Counter { private int count; public Counter() { count = 5; } public void increment() { count++; } public void reset() { count = 0; } public int value() { return count; } }If I have a subclass with a defined function (not implicitly created), does the subclass constructor inherit the instance variable count from the superclass constructor? I ask this because I'm running into a bit of a confusion with regards to private count.
public class ModNCounter extends Counter { int modCount; public ModNCounter(int n) { modCount = n; } @Override public int value() { return super.value() % modCount; } public static void main(String[] args) { ModNCounter modCounter = new ModNCounter(3); System.out.println(modCounter.value()); //prints out 5 % 3 = 2 modCounter.increment(); // count = 6 System.out.println(modCounter.value()); //prints out 6 % 3 = 0 modCounter.reset(); // count = 0 modCounter.increment(); // count = 1 System.out.println(modCounter.value()); //print 1 % 3 = 1 } }Does the object modCounter have a count variable? If not, why is modCounter.increment() not giving me an error?