Deck 3: Using Classes and Objects

Question 1

Which of the following is a correct declaration of enumerated type for the suits of a deck of cards?

A) enumerated type Suit = { hearts, spades, diamonds, clubs };
B) enum Suit {hearts, spades, diamonds, clubs };
C) enum Suit {hearts, spades, diamonds, clubs }
D) enumerated type Suit = {hearts, spades, diamonds, clubs };
E) enum Suit = { hearts, spades, diamonds, clubs }

Answer 1

C
Explanation: Choice c represents the correct syntax for declaring an enumerated type called Suit that can take one of the values hearts, spades, diamonds or clubs.

Question 2

Suppose we have a String object referenced by a variable called listing. Suppose we want a new String object that consists of the first 5 characters in listing. Which of the following lines of code will achieve this?

A) String prefix = listing.front(5);
B) String prefix = listing.front(6);
C) String prefix = listing.substring(1,5);
D) String prefix = listing.substring(0,5);
E) String prefix = listing.firstChars(5);

Answer 2

D
Explanation: Choices a, b, and e are wrong because the String class does not have methods called front or firstChars. Choice c is incorrect because the first character in the string is indexed by 1. Choice c is correct, since it will create a new string from the first 5 characters of listing.

Question 3

Assume that we have a Random object referenced by a variable called generator. Which of the following lines will generate a random number in the range 5-20 and store it in the int variable randNum?

A) randNum = generator.nextInt(15) + 5;
B) randNum = generator.nextInt(15) + 6;
C) randNum = generator.nextInt(16) + 5;
D) randNum = generator.nextInt(16) + 6;
E) none of the above

Answer 3

C
Explanation: When called with 16 as a parameter, the nextInt() method will return a number in the range 0 to 15. Adding 5 to this random number will generate a number in the range 5 to 20.

Question 4

When there are no references to an object, the object is marked as garbage and is automatically removed from memory using Java's automatic garbage collection feature.

Question 5

Which of the following classes include the getCurrencyInstance() method?

A) String
B) NumberFormat
C) DecimalFormat
D) Math
E) none of the above

Question 6

When an object variable is declared but it is not assigned a value, it is called a ______________________.

A) null reference
B) empty reference
C) void reference
D) zero reference
E) static reference

Question 7

Which of the following expressions correctly compute 5 + 2⁶?

A) result = 5 + 2^6;
B) result = 5 + 2*exponent(6);
C) result = 5 + 2*Math.exponent(6);
D) result = 5 + Math.pow(2, 6);
E) none of the above

Question 8

String objects can be changed after instantiation.

Question 9

Multiple reference variables can refer to the same object.

Question 10

A special method that is invoked to set up an object during instantiation is called a ___________________.

A) new method
B) dot operator
C) creator
D) constructor
E) destructor

Question 11

Which of the following represents the proper way to create a NumberFormat object that formats numbers as percentages?

A) NumberFormat fmt = new NumberFormat(%);
B) NumberFormat fmt = new NumberFormat("%");
C) NumberFormat fmt = NumberFormat.getPercentInstance();
D) NumberFormat fmt = new PercentNumberFormat();
E) none of the above

Question 12

A variable that is declared as a primitive type stores the actual value of the associated data. A variable that is declared as an object type stores a pointer to the associated object.

Question 13

____________________ is the automatic conversion between a primitive value and a corresponding wrapper object.

A) Generating
B) Aliasing
C) Number formatting
D) Static invocation
E) Autoboxing

Question 14

Which of the following is an invalid way to instantiate a String object?

A) String title = new String("Java Software Solutions");
B) String name = "John Lewis";
C) String empty = "";
D) String alsoEmpty = new String("");
E) all of the above are valid

Question 15

The new operator is used to access an objects methods.

Question 16

The String class _______________________________ .

A) is part of the java.lang package.
B) is part of the java.util.package.
C) is a wrapper class.
D) none of the above.
E) all of the above.

Question 17

The ________________ operator is used to instantiate an object.

A) static
B) new
C) +
D) -
E) none of the above

Question 18

Which of the following best describes what happens when an object no longer has any references pointing to it?

A) The object is overwritten the next time the new operator is called.
B) The object is overwritten the next time the new operator is called using the same class.
C) The object is immediately deleted from memory.
D) The object is marked as garbage and its associated memory is freed when the garbage collector runs.
E) The object stays in memory for the remainder of the programs execution.

Question 19

Consider the following snippet of code: Random generator = new Random();
Int randNum = generator.nextInt(20) + 1;
Which of the following will be true after these lines are executed?

A) randNum will hold a number between 1 and 20 inclusive.
B) randNum will hold a number between 0 and 20 inclusive.
C) randNum will hold a number between 1 and 21 inclusive.
D) these lines will not be executed because a compiler error will result.
E) none of the above

Question 20

When two references point to the same object, ________________________________ .

A) a run-time error will occur.
B) a compiler error will occur.
C) the references are called aliases of each other.
D) the object will be marked for garbage collection.
E) the references are called null references.

Question 21

Write a short program that asks the user to input a string, and then outputs the number of characters in the string.

Question 22

Write a single statement that creates a DecimalFormat object that formats numbers to 2 decimal places.

Question 23

When called with integer parameter n, the nextInt() method of the Random class will return a randomly generated integer between 0 and n.

Question 24

The Math class is part of the java.lang package.

Question 25

The System.out.printf() method is an alternative way to output information in Java.

Question 26

All of the classes contained in the java.util package are automatically included in every Java program.

Question 27

Suppose a Random object has been created called generator. Write a single statement that generates a random number in the range 73 to 100.

Question 28

Write a declaration for an enumerated type that represents the months of the year.

Question 29

Suppose we have a String object called myString. Write a single line of Java code that will output myString in such a way that all of its characters are uppercase.

Question 30

What is the range of integers that will be generated by the following expression?
generator.nextInt(15) + 5;

Question 31

Explain what it means for a String object to be immutable. Are there any workarounds for this?

Question 32

Write a short program that allows the user to enter the base and height of a triangle and outputs the hypotenuse, formatted to three decimal places.

Question 33

Explain how variables representing objects and variables representing primitive types are different.

Question 34

Write an expression that will compute the length of the tangent of a right triangle, given one of the non-right angles. You may assume that this value is stored in a variable called angle.

Question 35

What is output by the following code fragment?
String hello = new String("Hello World!");
hello = hello.replace('H', 'W');
hello = hello.replace('W', 'H');
System.out.println(hello);

Question 36

Write an expression that computes 12 raised to the power 4.3 and store the result in a double called result.

Question 37

Write a single line that creates a wrapper for an int variable num.

Question 38

Write a short program that allows the user to input a positive integer and then outputs a randomly generated integer between 1 and the input number.

Question 39

Enumerated types allow a programmer to treat primitive data as objects.

Question 40

Write a statement that computes the square root of a variable called discriminant and stores the value in a variable called result.