AP Computer Science Test 4 again
Multiple Choice Questions
For questions 1-3, use the
Student class definition
1) 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);
2) 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( )
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);
3) 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;
}
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 4-5.
4) 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");
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");
5) 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;
a) the
number of Heads flipped out of 1000 flips
b) the number of Heads flipped in a row out of
1000 flips
c) the
percentage of heads flipped out of 1000 flips
d) the percentage of
times neither Heads nor Tails were flipped out of 1000 flips
e) nothing
at all
6) 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
Use the following information to answer questions 7 -
8. The Die class from chapter 4 has two
constructors defined as follows. 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;
}
7) 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
8) 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
For questions 9-10, use the
Swapper class definition:
9) 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
10)
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"
11)
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);
12)
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
Question 13 refers to the
following method:
public int dogYears
(int age)
{
if (age >= 0)
return age * 7;
else
return 0;
}
13)
What would be an
appropriate precondition for the method?
a) // Precondition: tells how old your dog is
b) // Precondition: age is someone’s age
c) // Precondition: age >= 0
d) // Precondition: age is an int
e) // Precondition: returns age * 7
14)
What is a mutator method?
a) A method that modifies a value.
b) A method that provides read-only access to a value.
c) A method that has the same name, but different
parameters, as another method.
d) A method that is called when an object is first
created.
e) A method that does not return a value.
15)
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
True/False Questions:
16) Every class definition must include a
constructor.
17) While multiple objects of the same class can
exist, there is only one version of the class.
18) A class may contain methods but not variable declarations.
19) A constructor is a method that gets called
automatically whenever an object is created, for example with the new operator.
20) A constructor must have the same name as its
class.
21) A constructor must always return an int.
22) A class’s instance data are the variables
declared in the main method.
23) The methods in a class should always be made
public so that those outside the class can use them
24) The body of a method may be empty.
25) The return statement must be followed a
single variable that contains the value to be returned.
Free-form
Questions:
For
question 26, write the requested portion of a class called Employee.
26) An Employee will have a name, social security
number, position, and hourly wages. Define
the instance data for this class.
27) Assume a class has instance data String x, y,
z which were initialized in the class’ constructor. Write a method that will determine if any of
the three Strings store the same value as any of the other Strings. Return true if this is so, false otherwise.
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 + "\n" + major + "\n" + df.format(gpa) + "\n" + hours
}
}
public class Swapper
{
private int x;
private String y;
public int z;
public Swapper(int a, String b, int c)
{
x = a;
y = b;
z = c;
}
public String swap( )
{
int temp
= x;
x = z;
z = temp;
return y;
}
public String toString( )
{
if (x < z)
return y;
else return "" + x + z;
}
}
