Deck 3: Using Classes and Objects

Question 1

What is the function of the dot operator?

A) It serves to separate the integer portion from the fractional portion of a floating-point number.
B) It allows one to access the data within an object when given a reference to the object.
C) It allows one to invoke a method within an object when given a reference to the object.
D) It is used to terminate commands, similar to the way a period terminates a sentence in English.
E) Both B and C are correct.

Answer 1

E

Question 2

If two variables contain aliases of the same object then

A) the object may be modified using either alias
B) the object cannot be modified unless there's a single reference to it
C) a third alias is created if/when the object is modified
D) the object will become an "orphan" if both variables are set to null
E) answers A and D are both correct

Answer 2

E

Question 3

These two ways to set up a String will yield identical results:
String my_string = new String("123.45");
String my_string = "" + 123.45;

Answer 3

True

Question 4

When comparing any primitive type of variable, the == operator should always be used to test if two values are equal.

Question 5

These two ways to set up a String will yield identical results:
String my_string = "12345";
String my_string = 12345;

Question 6

These two ways to set up a String will yield identical results:
String my_string = new String(12345);
String my_string = new String("12345");

Question 7

In Java a variable may contain

A) a value or a reference
B) a package
C) a method
D) a class
E) Any of these

Question 8

What happens if you attempt to use a variable before it has been initialized?

A) A syntax error may be generated by the compiler.
B) A run-time error may occur during execution.
C) A "garbage" or "uninitialized" value will be used in the computation.
D) A value of zero is used.
E) Only answers A and B are correct.

Question 9

In Java, instantiation means

A) noticing the first time something is used
B) creating a new object of the class
C) creating a new alias for an existing object
D) launching a method
E) none of these

Question 10

Only difficult programming problems require a pseudocode solution before the programmer creates the program itself.

Question 11

If you need to import not only the top-level of a package, but all its secondary levels as well, you should use the following:
import package.*.*;

Question 12

The printf method within System.out is designed to ease the conversion of legacy C code into Java.

Question 13

Which properties are true of String objects?

A) Their lengths never change.
B) The shortest String has zero length.
C) Individual characters within a String may be changed using the replace method.
D) The index of the first character in a String is one.
E) Only answers A and B are true.

Question 14

In Java, the symbol "=" and the symbol "==" are used interchangeably.

Question 15

The following statement will display the value 127.
System.out.println("123" + 4);

Question 16

These two ways to set up a String will yield identical results:
String my_string = new String("a bunch of words");
String my_string = "a bunch of words";

Question 17

You may apply the prefix and postfix increment and decrement operators to instances of the Integer class.

Question 18

You may use the String.replace() method to remove characters from a String.

Question 19

The names of the wrapper classes are just the names of the primitive data types, but with an initial uppercase letter.

Question 20

All the methods in the Math class are declared to be static.

Question 21

Java.text's NumberFormat class includes methods that

A) allow you to format currency
B) allow you to format percentages
C) round their display during the formatting process
D) truncate their display during the formatting process
E) A, B, C, but not D

Question 22

An alias is when

A) two different reference variables refer to the same physical object
B) two different numeric variables refer to the same physical object
C) two different numeric variables contain identical values
D) two variables have the same name
E) None of these

Question 23

Which is now the preferred approach for developing Java programs that use graphics and GUIs?

A) Swing
B) AWT
C) JavaFX
D) API
E) All of these are preferred approaches

Question 24

Consider the condition (x == y). How is this handled if x and y are primitive types? How is this handled if x and y are objects?

Question 25

Which of the following packages includes classes that represent shapes in JavaFX?

A) javafx.scene.shape
B) javafx.shape.scene
C) javafx.shapes
D) javafx.stage.shape
E) javafx.stage.scene

Question 26

Which of the following will yield a pseudorandom number in the range [-5, +5), given: Random gen = new Random();

A) gen.nextFloat()*5
B) gen.nextFloat()*10-5
C) gen.nextFloat()*5-10
D) gen.nextInt()*10-5
E) gen.nextInt(10)-5

Question 27

The String class's compareTo method

A) compares two strings in a case-independent manner
B) yields true or false
C) yields 0 if the two strings are identical
D) rerturns 1 if the first string comes lexically before the second string
E) None of these

Question 28

In the StringMutation program shown in Listing 3.1, if phrase is initialized to "Einstein", what will Mutation # 3 yield if mutation1 = phrase.concat(".")?

A) Einstein.
B) EINSTEIN.
C) XINSTXIN.
D) einstein.
E) xinstxin.

Question 29

Which statement is true, given the following code fragment? String strA = "aBcDeFg";
String strB = strA.toLowerCase();
StrB = strB.toUpperCase();
String strC = strA.toUpperCase();

A) strB.equals(strC) would be true
B) strB.compareTo(strC) would yield 0
C) strA.equals(strC) would be true
D) strA.compareTo(strC) would yield 0
E) None of these

Question 30

What does the following code fragment do? Circle circle = new Circle(100, 100, 50);
Circle.setFill(Color.GREEN);
Rectangle rectangle = new Rectangle(70, 70, 225, 75);
Rectangle.setStroke(Color.BLUE);
Rectangle.setStrokeWidth(2);
Rectangle.setFill(null);

A) It creates a green circle, centered at coordinates (100, 100).
B) It creates a rectangle which overlaps the circle since its upper-left corner is at coordinates (70, 70) and its dimensions are 225 X 75.
C) Since the rectangle's fill color is set to null, the circle will be visible through the rectangle.
D) The rectangle will have a blue border.
E) All of these are true.

Question 31

The advantages of the DecimalFormat class compared to the NumberFormat class include

A) precise control over the number of digits to be displayed
B) control over the presence of a leading zero
C) the ability to truncate values rather than round them
D) the ability to display a percent sign (%) automatically at the beginning of the display
E) only A and B

Question 32

Write a declaration for a Rectangle named squareShape that is 400 pixels wide, 400 pixels high, and its upper-left corner position is at point (50, 50).

A) Rectangle squareShape = new squareShape(50, 50, 400, 400);
B) squareShape = new Rectangle(50, 50, 400, 400);
C) Rectangle squareShape = new Rectangle(50, 400, 50, 400);
D) Rectangle squareShape = new Rectangle(50, 50, 400, 400);
E) Rectangle = new squareShape(400, 400, 50, 50);

Question 33

Given the following two lines of code, what can be said about s1 and s2? String s1 = "testing" + "123";
String s2 = new String("testing 123");

A) s1 and s2 are both references to the same String object.
B) the line declaring s1 is legal in Java; the line declaring s2 will produce a syntax error.
C) s1 and s2 are references to different String objects.
D) s1 and s2 will compare "equal."
E) None of the above

Question 34

In a development environment that fully supports JavaFX, which of the following is true?

A) The launch method of the scene class is called automatically.
B) The launch method of the Application class is called automatically.
C) Since the launch method is called automatically, you do not need to write the main method.
D) Since the launch method is called automatically, you do not need to call it in the main method.
E) Both B and C are true

Question 35

Assume you write a program that uses the Random class but you fail to include an import statement for java.util.Random or java.util.*. What will happen when you attempt to compile and run your program?

A) The program won't run but it will compile with a warning about missing the class.
B) The program won't compile and you'll receive a syntax error about the missing class.
C) The program will compile but you'll receive a warning about the missing class.
D) The program will encounter a run-time error when it attempts to access any member of the Random class.
E) none of these

Question 36

In addition to providing a mechanism to convert primitive data into objects, what else do the wrapper classes provide?

A) enumerations
B) static constants
C) arrays to contain the data
D) exceptions
E) None of these

Question 37

An API is

A) an Abstract Programming Interface
B) an Application Programmer's Interface
C) an Application Programming Interface
D) an Abstract Programmer's Interface
E) an Absolute Programming Interface

Question 38

The advantage(s) of the Random class's pseudorandom number generators, compared to the Math.random method, is(are) that

A) you may create several random number generators
B) the generators in Random are more efficient than the one in Math.random
C) you can generate random ints, floats, and ints within a range
D) you can initialize and reinitialize Random generators
E) all except B are true

Question 39

What will be displayed by the following command? System.out.println(Math.pow(3, 3-1));

A) 9
B) 8
C) 6
D) 4
E) 27

Question 40

Rewrite the following five assignment statements into a single statement using prefix and postfix increment and decrement operators as necessary. Assume all variables are int variables.
x = y + 1;
y = y + 1;
z = z - 1;
x = x - z;
x = x + 1;

Question 41

Refer to Problem Ch 03-1. Write a method to extract the initial from the first name.

Question 42

Refer to Problem Ch 03-1. For the program to get a name interactively a Scanner object must be instantiated. Write the Java statement to do this.

Question 43

Refer to Problem Ch 03-1. Write a statement to guarantee that the initial will be a capital letter.

Question 44

Why is it often a good idea to group particular elements together in a scene?

Question 45

Refer to Problem Ch 03-1. Write a statement using a Scanner method to get the first name interactively.

Question 46

What is a wrapper class? Why are wrapper classes useful?

Question 47

Given two String variables, s1 and s2, is it possible for (s1 != s2)to be true while (s1.equals(s2)) is also true? Why or why not?

Question 48

Write a statement to create a Color object equivalent to Color.ORANGE using the rgb method.

Question 49

What is autoboxing?