11 Javanotes 9.0, Quiz on Chapter 5

Quiz on Chapter 5

Question 1:

Object-oriented programming
uses classes and objects. What are classes and what are objects?
What is the relationship between classes and objects?

Question 2:

Explain carefully what
null means in Java, and why this special value is necessary.

Question 3:

What is a
constructor? What is the purpose of a constructor in a class?

Question 4:

Suppose that
Kumquat is the name of a class and that fruit is a variable
of type Kumquat. What is the meaning of the statement “fruit = new
Kumquat();“? That is, what does the computer do when it executes this
statement? (Try to give a complete answer. The computer does several
things.)

Question 5:

What is meant by the terms
instance variable and instance method?

Question 6:

Explain what is meant by the
terms subclass and superclass.

Question 7:

Modify the following class so that the two instance variables are private
and there is a getter method and a setter method for each instance variable:

public class Player {
   String name;
   int score;
}

Question 8:

Explain why the class Player that is defined in the previous
question has an instance method named toString(), even though no definition
of this method appears in the definition of the class.

Question 9:

Explain the term
polymorphism.

Question 10:

Java uses “garbage
collection” for memory management. Explain what is meant here by garbage
collection. What is the alternative to garbage collection?

Question 11:

What is an abstract class, and how can you recognize an abstract class in Java?

Question 12:

What is this?

Question 13:

For this problem, you should
write a very simple but complete class. The class represents a counter that
counts 0, 1, 2, 3, 4, …. The name of the class should be Counter. It
has one private instance variable representing the value of the
counter. It has two instance methods: increment() adds one to the
counter value, and getValue() returns the current counter value. Write
a complete definition for the class, Counter.

Question 14:

This problem uses the
Counter class from the previous question. The following program segment is meant
to simulate tossing a coin 100 times. It should use two Counter
objects, headCount and tailCount, to count the number of
heads and the number of tails. Fill in the blanks so that it will do so:

Counter headCount, tailCount;
tailCount = new Counter();
headCount = new Counter();
for ( int flip = 0;  flip < 100;  flip++ ) {
   if (Math.random() < 0.5)    // There's a 50/50 chance that this is true.
   
       ______________________ ;   // Count a "head".
       
   else
   
       ______________________ ;   // Count a "tail".
}

System.out.println("There were " + ___________________ + " heads.");

System.out.println("There were " + ___________________ + " tails.");

Question 15:

Explain why it can never make sense to test “if (obj.equals(null))“.

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