Section 1
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. Assume MIN_FACES is an int equal to 4. public Die( ) public Die(int faces) { { numFaces = 6; if(faces < MIN_FACES) numFaces = 6; faceValue = 1; else numFaces = faces; } faceValue = 1; } 20) The instruction Die d = new Die(10, 0); results in a) The Die d having numFaces = 6 and faceValue = 1 b) The Die d having numFaces = 10 and faceValue = 1 c) The Die d having numFaces = 10 and faceValue = 10 d) The Die d having numFaces = 6 and faceValue = 10 e) A syntax error
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Section 1
(50 cards)
. Assume MIN_FACES is an int equal to 4. public Die( ) public Die(int faces) { { numFaces = 6; if(faces < MIN_FACES) numFaces = 6; faceValue = 1; else numFaces = faces; } faceValue = 1; } 20) The instruction Die d = new Die(10, 0); results in a) The Die d having numFaces = 6 and faceValue = 1 b) The Die d having numFaces = 10 and faceValue = 1 c) The Die d having numFaces = 10 and faceValue = 10 d) The Die d having numFaces = 6 and faceValue = 10 e) A syntax error
Answer: e. Explanation: The Die class has two constructors, one that receives no parameters and one that receives a single int parameter. The instruction above calls the Die constructor with 2 int parameters. Since no constructor matches this number of parameters exists, a syntax error occurs
12) A constructor is a method that gets called automatically whenever an object is created, for example with the new operator.
Answer: True. The constructor is used to initialize an object and it gets called whenever a new object is created from a particular class.
12) An example of passing a message to a String where the message has a String parameter occurs in which of the following messages? a) length b) substring c) equals d) toUpperCase e) none of the above, it is not possible to pass a String as a parameter in a message to a String
Answer: c. Explanation: The length and toUpperCase messages do not have parameters and substring has two int parameters. For equals, a String must be passed as a parameter so that the String receiving the message can be compared to the String passed as a parameter.
21) If the instruction Swapper s = new Swapper(0, "hello", 0); is executed followed by s.toString( ); what value is returned from s.toString( )? a) "hello" b) "hello00" c) "00" d) "0" e) 0
Answer: c. Explanation: The toString method compares x and z, and if x < y it returns the String y. In this case, x == z, so the else clause is executed, and the String of "" + x + z is returned. This is the String "00".
11) A class may contain methods but not variable declarations.
Answer: False. A class may contain both methods and variable declarations.
25) An object may be made up of other objects
Answer: True. An aggregate object is an object that has other objects as instance data.
25) Consider a method defined with the header: public void doublefoo(double x). Which of the following method calls is legal? a) doublefoo(0); b) doublefoo(0.555); c) doublefoo(0.1 + 0.2); d) doublefoo(0.1, 0.2); e) all of the above are legal except for d
Answer: e. Explanation: In the case of a, the value 0 (an int) is widened to a double. In the case of c, the addition is performed yielding 0.3 and then doublefoo is called. The parameter list in d is illegal since it contains two double parameters instead of 1.
For questions 13-15, use the following class definition
import java.text.DecimalFormat;
public class Student
{
private String name;
private String major;
private double gpa;
private int hours;
public Student(String newName, String newMajor, double newGPA, int newHours)
{
name = newName;
major = newMajor;
gpa = newGPA;
hours = newHours;
}
public String toString( )
{
DecimalFormat df = new DecimalFormat("xxxx"); // xxxx needs to be replaced
return name + "
" + major + "
" + df.format(gpa) + "
" + hours
}
}
14) Assume that another method has been defined that will compute and return the student's class rank (Freshman,
Sophomore, etc). It is defined as:
public String getClassRank( )
TB 38 Lewis/Loftus/Cocking: Chapter 4 Test Bank
Given that s1 is a student, which of the following would properly be used to get s1's class rank?
a) s1 = getClassRank( );
b) s1.toString( );
c) s1.getHours( );
d) s1.getClassRank( );
e) getClassRank(s1);
Answer: d. Explanation: To call a method of an object requires passing that object a message which is the same as the method name, as in object.methodname(parameters). In this situation, the object is s1, the method is getClassRank, and this method expects no parameters. Answers a and e are syntactically illegal while answer b returns information about the Student but not his/her class rank, and there is no "getHours" method so c is also syntactically illegal
3) All Java classes must contain a main method which is the first method executed when the Java class is called upon.
Answer: False. Explanation: Only the driver program requires a main method. The driver program is the one that is first executed in any Java program (except for Applets), but it may call upon other classes as needed, and these other classes do not need main methods
. Assume MIN_FACES is an int equal to 4. public Die( ) public Die(int faces) { { numFaces = 6; if(faces < MIN_FACES) numFaces = 6; faceValue = 1; else numFaces = faces; } faceValue = 1; } 19) The instruction Die d = new Die(10); results in a) The Die d having numFaces = 6 and faceValue = 1 b) The Die d having numFaces = 10 and faceValue = 1 c) The Die d having numFaces = 10 and faceValue = 10 d) The Die d having numFaces = 6 and faceValue = 10 e) A syntax error
Answer: b. Explanation: Since an int parameter is passed to the constructor, the second constructor is executed, which sets numFaces = 10 (since numFaces >= MIN_FACES) and faceValue = 1.
19) The number and types of the actual parameters must match the number and types of the formal parameters
Answer: True. The names of the corresponding actual and formal parameters may be different but the number and types of the parameters must match.
6) A method defined in a class can access the class' instance data without needing to pass them as parameters or declare them as local variables.
Answer: True. Explanation: The instance data are globally available to all of the class' methods and therefore the methods do not need to receive them as parameters or declare them locally. If variables of the same name as instance data were declared locally inside a method then the instance data would be "hidden" in that method because the references would be to the local variables.
14) A constructor must always return an int
Answer: False. In fact, a constructor cannot return anything. It has no return value, not even void. When a constructor is written, no return value should be listed.
7) The interface of a class is based on those data instances and methods that are declared public.
Answer: True. Explanation: The interface is how an outside agent interacts with the object. Interaction is only available through those items declared to be public in the class' definition.
8) Defining formal parameters requires including each parameters type
Answer: True. Explanation: In order for the compiler to check to see if a method call is correct, the compiler needs to know the types for the parameters being passed. Therefore, all formal parameters (those defined in the method header) must include their type. This is one element that makes Java a Strongly Typed language.
2) The relationship between a class and an object is best described as a) classes are instances of objects b) objects are instances of classes c) objects and classes are the same thing d) classes are programs while objects are variables e) objects are the instance data of classes
Answer: b. Classes are definitions of program entities that represent classes of things/entities in the world. Class definitions include instance data and methods. To use a class, it is instantiated. These instances are known as objects. So, objects are instances of classes. Program code directly interacts with objects, not classes.
16) The methods in a class should always be made public so that those outside the class can use them
Answer: False. Methods that need to be available for use outside a class should be made public, but methods that will only be used inside the class should be made private.
10) Having multiple class methods of the same name where each method has a different number of or type of parameters is known as a) encapsulation b) information hiding c) tokenizing d) importing e) method overloading
Answer: e. Explanation: When methods share the same name, they are said to be overloaded. The number and type of parameters passed in the message provides the information by which the proper method is called.
13) A constructor must have the same name as its class.
Answer: True. A constructor is required to have the same name as the class.
23) If we have Swapper r = new Swapper (5, "no", 10); then r.swap( ); returns which of the following? a) nothing b) "no" c) "no510" d) "510" e) "15"
Answer: b. Explanation: The swap method swaps the values of x and z (thus x becomes 10 and z becomes 5) and returns the value of y, which is "no" for r.
10) While multiple objects of the same class can exist, there is only one version of the class
Answer: True. Explanation: A class is an abstraction, that is, it exists as a definition, but not as a physical instance. Physical instances are created when an object is instantiated using new. Therefore, there can be many objects of type String, but only one String class.
9) Every class definition must include a constructor.
Answer: False. Explanation: Java allows classes to be defined without constructors, however, there is a default constructor that is used in such a case.
For questions 13-15, use the following class definition
import java.text.DecimalFormat;
public class Student
{
private String name;
private String major;
private double gpa;
private int hours;
public Student(String newName, String newMajor, double newGPA, int newHours)
{
name = newName;
major = newMajor;
gpa = newGPA;
hours = newHours;
}
public String toString( )
{
DecimalFormat df = new DecimalFormat("xxxx"); // xxxx needs to be replaced
return name + "
" + major + "
" + df.format(gpa) + "
" + hours
}
}
15) Another method that might be desired is one that updates the Student's number of credit hours. This method will
receive a number of credit hours and add these to the Student's current hours. Which of the following methods
would accomplish this?
a) public int updateHours( )
{
return hours;
}
b) public void updateHours( )
{
hours++;
}
c) public updateHours(int moreHours)
{
hours += moreHours;
}
d) public void updateHours(int moreHours)
{
hours += moreHours;
}
e) public int updateHours(int moreHours)
{
return hours + moreHours;
}
Answer: d. Explanation: This method will receive the number of new hours and add this to the current hours. The method in d is the only one to do this appropriately. Answer c is syntactically invalid since it does not list a return type. The answer in e returns the new hours, but does not reset hours appropriately. The Coin class, as defined in Chapter 4, consists of a constructor, and methods flip, isHeads and toString. The method isHeads returns true if the last flip was a Heads, and false if the last flip was a Tails. The toString method returns a String equal to "Heads" or "Tails" depending on the result of the last flip. Using this information, answer questions 16 - 17
9) A class' constructor usually defines a) how an object is initialized b) how an object is interfaced c) the number of instance data in the class d) the number of methods in the class e) if the instance data are accessible outside of the object directly
Answer: a. Explanation: The constructor should be used to "construct" the object, that is, to set up the initial values of the instance data. This is not essential, but is typically done. The interface of an object is dictated by the visibility modifiers used on the instance data and methods.
4) Which of the following reserved words in Java is used to create an instance of a class? a) class b) public c) public or private, either could be used d) import e) new
Answer: e. Explanation: The reserved word "new" is used to instantiate an object, that is, to create an instance of a class. The statement new is followed by the name of the class. This calls the class' constructor. Example: Car x = new Car( ); will create a new instance of a Car and set the variable x to it.
4) Java methods can return more than one item if they are modified with the reserved word continue, as in public continue int foo( ) { ... }
Answer: False. Explanation: All Java methods return a single item, whether it is a primitive data type an object, or void. The reserved word continue is used to exit the remainder of a loop and test the condition again.
16) A set of code has already instantiated c to be a Coin and has input a String guess, from the user asking whether the user guesses that a coin flip will result in "Heads" or "Tails". Which of the following sets of code will perform the coin flip and see if the user's guess was right or wrong? a) c.flip( ); if(c.isHeads( ).equals(guess)) System.out.println("User is correct"); b) if(c.flip( ).equals(guess)) System.out.println("User is correct"); c) if(c.isHeads( ).equals(guess)) System.out.println("User is correct"); Lewis/Loftus/Cocking: Chapter 4 Test Bank TB 39 d) c.flip( ); if(c.toString( ).equals(guess)) System.out.println("User is correct"); e) c.flip( ).toString( ); if(c.equals(guess)) System.out.println("User is correct");
Answer: d. Explanation: c.flip( ) must be performed first to get a Coin flip. Next, the user's guess is compared against the value of the Coin's flip. The Coin c stores the result as an int and the user's guess is a String. Using getFace( ) returns the int value but using the toString method will return the String "Heads" or "Tails". So, the code compares c.toString( ) with the user's guess using the String method equals.
24) Consider a method defined with the header: public void foo(int a, int b). Which of the following method calls is legal? a) foo(0, 0.1); b) foo(0 / 1, 2 * 3); c) foo(0); d) foo( ); e) foo(1 + 2, 3 * 0.1);
Answer: b. Explanation: The only legal method call is one that passes two int parameters. In the case of answer b, 0 / 1 is an int division (equal to 0) and 2 * 3 is an int multiplication. So this is legal. The answers for a and e contain two parameters, but the second of each is a double. The answers for c and d have the wrong number of parameters.
17) What does the following code compute? int num = 0; for(int j = 0; j < 1000; j++) { c.flip( ); if(c.isHeads()) num++; } double value = (double) num / 1000; 1) the number of Heads flipped out of 1000 flips 2) the number of Heads flipped in a row out of 1000 flips 3) the percentage of heads flipped out of 1000 flips 4) the percentage of times neither Heads nor Tails were flipped out of 1000 flips 5) nothing at all
Answer: c. Explanation: The code iterates 1000 times, flipping the Coin and testing to see if this flip was a 0 ("Heads") or 1 ("Tails"). The variable num counts the number of Heads and the variable value is then the percentage of Heads over 1000
7) Consider a sequence of method invocations as follows: main calls m1, m1 calls m2, m2 calls m3 and then m2 calls m4, m3 calls m5. If m4 has just terminated, what method will resume execution? a) m1 b) m2 c) m3 d) m5 e) main
Answer: b. Explanation: Once a method terminates, control resumes with the method that called that method. In this case, m2 calls m4, so that when m4 terminates, m2 is resumed.
1) The behavior of an object is defined by the object's a) instance data b) constructor c) visibility modifiers d) methods e) all of the above
Answer: d. Explanation: The methods dictate how the object reacts when it is passed messages. Each message is implemented as a method, and the method is the code that executes when the message is passed. The constructor is one of these methods but all of the methods combine dictate the behavior. The visibility modifiers do impact the object's performance indirectly.
15) A class's instance data are the variables declared in the main method.
Answer: False. A class's instance data are declared in the class but not inside any method. Variables declared in a method are local to that method and can only be used in that method. Furthermore, every class need not have a main method.
17) The body of a method may be empty.
Answer: True. The method body may have 0 or more instructions, so it could have 0. An empty method body is simply { } with no statements in between.
24) Method decomposition is the process of creating overloaded versions of a method that do the same thing, but operate on different data types.
Answer: False. Method decomposition is breaking a complicated method into simpler methods to create a more understandable design
6) If a method does not have a return statement, then a) it will produce a syntax error when compiled b) it must be a void method c) it can not be called from outside the class that defined the method d) it must be defined to be a public method e) it must be an int, double, or String method
Answer: b. Explanation: All methods are implied to return something and therefore there must be a return statement. However, if the programmer wishes to write a method that does not return anything, and therefore does not need a return statement, then it must be a void method (a method whose header has "void" as its return type).
21) If a method takes a double as a parameter, you could pass it an int as the actual parameter
Answer: True. Since converting from an int to a double is a widening conversion, it is done automatically, so there would be no error.
23) The println method on System.out is overloaded
Answer: True. The println method includes versions that take a String, int, double, char, and boolean.
8) A variable whose scope is restricted to the method where it was declared is known as a(n) a) parameter b) global variable c) local variable d) public instance data e) private instance data
Answer: c. Explanation: Local variables are those that are "local" to the method in which they have been declared, that is, they are accessible only inside that method. Global variables are those that are accessible from anywhere, while parameters are the variables passed into a method. Instance data can be thought of as global variables for an entire object.
11) Instance data for a Java class a) are limited to primitive types (e.g., int, double, char) b) are limited to Strings c) are limited to objects(e.g., Strings, classes defined by other programmers) d) may be primitive types or objects, but objects must be defined to be private e) may be primitive types or objects
Answer: e. Explanation: The instance data are the entities that make up the class and may be any type available whether primitive or object, and may be public or private. By using objects as instance data, it permits the class to be built upon other classes. This relationship where a class has instance data that are other classes is known as a has-a relationship.
18) The return statement must be followed a single variable that contains the value to be returned.
Answer: False. The return statement may be following by any expression whose type is the same as the declared return type in the method header. For example, return x*y+6; is a valid return statement. The statement return; is also valid for a method that does not return anything (void).
18) In the Rational class, defined in chapter 4, the methods reduce and gcd are declared to be private. Why? a) Because they will never be used b) Because they will only be called from methods inside of Rational c) Because they will only be called from the constructor of Rational d) Because they do not use any of Rational's instance data e) Because it is a typo and they should be declared as public
Answer: b. Explanation: All items of a class that are declared to be private are only accessible to entities within that class, whether they are instance data or methods. In this case, since these two methods are only called from other methods (including the constructor) of Rational, they are declared private to promote information hiding to a greater degree. Note that answer c is not a correct answer because the reduce method calls the gcd method, so one of the methods is called from a method other than the constructor.
20) The different versions of an overloaded method are differentiated by their signatures
Answer: True. A method's signature include the number, types, and order of its parameters. With overloaded methods, the name is the same, but the the methods must differ in their parameters.
2) Formal parameters are those that appear in the method call and actual parameters are those that appear in the method header
Answer: False. Explanation: The question has the two definitions reversed. Formal parameters are those that appear in the method header, actual parameters are the parameters in the method call (those being passed to the method).
22) Which of the following criticisms is valid about the Swapper class? a) The instance data x is visible outside of Swapper b) The instance data y is visible outside of Swapper c) The instance data z is visible outside of Swapper d) All 3 instance data are visible outside of Swapper e) None of the methods are visible outside of Swapper
Answer: c. Explanation: We would expect none of the instance data to be visible outside of the class, so they should all be declared as "private" whereas we would expect the methods that make up the interface to be visible outside of the class, so they should all be declared as "public". We see that z is declared "public" instead of "private".
22) A method defined without a return statement will cause a compile error.
Answer: False. If a method is declared to return void then it doesn't need a return statement. However, if a method is declared to return a type other than void, then it must have a return statement.
1) Java methods can return only primitive types (int, double, boolean, etc).
Answer: False. Explanation: Java methods can also return objects, such as a String.
5) The following method header definition will result in a syntax error: public void aMethod( );
Answer: True. Explanation: The reason for the syntax error is because it ends with a ";" symbol. It instead needs to be followed by { } with 0 or more instructions inside of the brackets. An abstract method will end with a ";" but this header does not define an abstract method.
For questions 13-15, use the following class definition
import java.text.DecimalFormat;
public class Student
{
private String name;
private String major;
private double gpa;
private int hours;
public Student(String newName, String newMajor, double newGPA, int newHours)
{
name = newName;
major = newMajor;
gpa = newGPA;
hours = newHours;
}
public String toString( )
{
DecimalFormat df = new DecimalFormat("xxxx"); // xxxx needs to be replaced
return name + "
" + major + "
" + df.format(gpa) + "
" + hours
}
}
13) Which of the following could be used to instantiate a new Student s1?
a) Student s1 = new Student( );
b) s1 = new Student( );
c) Student s1 = new Student("Jane Doe", "Computer Science", 3.333, 33);
d) new Student s1 = ("Jane Doe", "Computer Science", 3.333, 33);
e) new Student(s1);
Answer: c. Explanation: To instantiate a class, the object is assigned the value returned by calling the constructor preceded by the reserved word new, as in new Student( ). The constructor might require parameters, and for Student, the parameters must be are two String values, a double, followed by an int.
3) To define a class that will represent a car, which of the following definitions is most appropriate? a) private class car b) public class car c) public class Car d) public class CAR e) private class Car
Answer: c. Explanation: Classes should be defined to be public so that they can be accessed by other classes. And following Java naming convention, class names should start with a capital letter and be lower case except for the beginning of each new word, so Car is more appropriate than car or CAR.
5) In order to preserve encapsulation of an object, we would do all of the following except for which one? a) Make the instance data private b) Define the methods in the class to access and manipulate the instance data c) Make the methods of the class public d) Make the class final e) All of the above preserve encapsulation
Answer: d. Explanation: Encapsulation means that the class contains both the data and the methods needed to manipulate the data. In order to preserve encapsulation properly, the instance data should not be directly accessible from outside of the classes, so the instance data are made private and methods are defined to access and manipulate the instance data. Further, the methods to access and manipulate the instance data are made public so that other classes can use the object. The reserved word "final" is usedto control inheritance and has nothing to do with encapsulation.
Section 2
(50 cards)