Questions 1–3 refer to the Time class declared below.
public class Time
{
private int hrs ;
private int mins ;
private int secs ;
public Time () {
/* implementation not shown */
}
public Time (int h, int m, int s) {
/* implementation not shown */
}
/** Resets time to hrs = h, mins = m, secs = s. */
public void resetTime (int h, int m, int s) {
/* implementation not shown */
}
/** Advances time by one second . */
public void increment () {
/* implementation not shown */
}
/** Returns true if this time equals t,
* false otherwise . */
public boolean equals ( Time t) {
/* implementation not shown */
}
/** Returns true if this time is earlier than t,
* false otherwise */
public boolean lessThan ( Time t) {
/* implementation not shown */
}
/** Returns a String with the time
* in the form hrs:mins:secs. */
public String toString () {
/* implementation not shown */
}
}
1. Which of the following is a false statement about the methods?
A. equals, lessThan, and toString are all accessor methods.
B. increment is a mutator method.
C. Time() is the no-argument constructor.
D. The Time class has three constructors.
E. There are no static methods in this class.
2. Which of the following represents correct implementation code for the constructor
with parameters?
A. hrs = 0;
mins = 0;
secs = 0;
B. hrs = h;
mins = m;
secs = s;
C. resetTime (hrs , mins , secs );
D. h = hrs ;
m = mins ;
s = secs ;
E. Time = new Time (h, m, s);
3. A client class has a display method that writes the time represented by its parame-
ter:
/** Outputs time t in the form hrs:mins:secs. */
public void display ( Time t) {
/* method body */
}
Which of the following are correct replacements for /* method body*/?
I. Time T = new Time (h, m, s);
System . out . println (T);
II. System . out . println (t. hrs + ":" +
t. mins + ":" +
t. secs );
III. System . out . println (t);
A. I only
B. II only
C. III only
D. II and III only
E. I, II and III
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4. Which statement about parameters is false?
A. The scope of parameters is the method in which they are defined.
B. Static methods have no implicit parameter this.
C. Two overloaded methods in the same class must have parameters with dif-
ferent names.
D. All parameters in Java are passed by value.
E. Two different constructors in a given class can have the same number of
parameters.
Questions 5–11 refer to the following Date class declaration.
public class Date
{
private int day ;
private int month ;
private int year ;
public Date () //no - argumen constructor
{
...
}
public Date (int mo , int da , int yr) // constructor
{
...
}
public int month () // returns month of Date
{
public int day () // returns day of Date
{
public int year () // returns year of Date
{
// Returns String representation of Date as "m/d/y",
//e.g. 4/18/1985.
public String toString ()
{
...
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}
}
5. Which of the following correctly constructs a Date object in a client class?
A. Date d = new (2 , 13 , 1947) ;
B. Date d = new Date (2 , 13 , 1947) ;
C. Date d;
d = new (2 , 13 , 1947) ;
D. Date d;
d = Date (2 , 13 , 1947) ;
E. Date d = Date (2 , 13 , 1947) ;
6. Which of the following will cause an error message?
I. Date d1 = new Date (8 , 2, 1947) ;
Date d2 = d1;
II. Date d1 = null ;
Date d2 = d1;
III. Date d = null ;
int x = d. year ();
A. I only
B. II only
C. III only
D. II and III only
E. I, II and III
7. A client program creates a Date object as follows.
Date d = new Date (1 , 13 , 2002) ;
Which of the following subsequent code segments will cause an error?
A. String s = d. toString ();
B. int x = d. day ();
C. Date e = d;
D. Date e = new Date (1 , 13 , 2002) ;
E. int y = d. year ;
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8. Consider the implementation of a write() method that is added to the Date class.
/** Write the date in the form m/d/y, e.g. 2/17/1948. */
public void write () {
/* implementation code */
}
Which of the following could be used as /* implementation code */?
I. System . out . println ( month + "/" +
day + "/" + year );
II. System . out . println ( month () + "/" +
day () + "/" + year ());
III. System . out . println ( this );
A. I only
B. II only
C. III only
D. II and III only
E. I, II and III
9. Here is a client program that uses Date objects:
public class BirthdayStuff {
public static Date findBirthdate () {
/* code to get birthDate */
return birthDate ;
}
public static void main ( String [] args ) {
Date d = findBirthdate ();
...
}
}
Which of the following is a correct replacement for /* code to get birthDate */?
I. System . out . println (" Enter birthday : mo , day , yr:");
int m = ...; // read user input
int d = ...; // read user input
int y = ...; // read user input
Date birthDate = new Date (m, d, y);
II. System . out . println (" Enter birthday : mo , day , yr:");
int birthDate . month () = ...; // read user input
int birthDate . day () = ...; // read user input
int birthDate . year () = ...; // read user input
Date birthDate = new Date ( birthDate . month () ,
birthDate . day () ,
birthDate . year ());
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III. System . out . println (" Enter birthday : mo , day , yr:");
int birthDate . month = ...; // read user input
int birthDate . day = ...; // read user input
int birthDate . year = ...; // read user input
Date birthDate = new Date ( birthDate . month ,
birthDate .day ,
birthDate . year );
A. I only
B. II only
C. III only
D. I and II only
E. II and III only
10. A method in a client program for the Date class has the following declaration.
Date d1 = new Date (mo , da , yr);
Here, mo, da, and yr are previously defined integer variables. The same method now
creates a second Date object d2 that is an exact copy of the object d1 refers to. Which
of the following code segments will not do this correctly?
I. Date d2 = d1;
II. Date d2 = new Date (mo , da , yr);
III. Date d2 = new Date (d1. month () , d1. day () , d1. year ());
A. I only
B. II only
C. III only
D. II and III only
E. I, II and III
11. The Date class is modified by adding the following mutator method:
public void addYears (int n) // add n years to date
Here is part of a poorly coded client program that uses the Date class:
public static void addCentury ( Date recent , Date old )
{
old . addYears (100) ;
recent = old ;
}
public static void main ( String [] args )
{
Date oldDate = new Date (1 , 13 , 1900) ;
Date recentDate = null ;
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addCentury ( recentDate , oldDate );
...
}
Which will be true after executing this code?
A. A NullPointerException is thrown.
B. The oldDate object remains unchanged.
C. recentDate is a null reference.
D. recentDate refers to the same object as oldDate.
E. recentDate refers to a separate object whose contents are the same as those
of oldDate.
12. Here are the private instance variables for a Frog object:
public class Frog
{
private String species ;
private int age ;
private double weight ;
private position position ; // position (x, y) in pond
private boolean amAlive ;
...
}
Which of the following methods in the Frog class is the best candidate for being a
static method?
A. swim // frog swims to new position in pond
B. getPondTemperature // return temperature of pond
C. eat // frog eats and gains weight
D. getWeight // returns weight of frog
E. die // frog dies with some probability based
//on frog 's age and pond temperature
13. What output will be produced by this program?
public class Mystery
{
public static void strangeMethod (int x, int y)
{
x += y;
y *= x;
System . out . println (x + " " + y);
}
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public static void main ( Stirng [] args )
{
int a = 6, b = 3;
strangeMethod (a, b)
System . out . println (a + " " + b);
}
}
A. 36
9
B. 3 6
9
C. 9 27
9 27
D. 6 3
9 27
E. 9 27
6 3
Questions 14–17 refer to the following definition of the Rational class.
public class Rational
{
private int numerator ;
private int denominator ;
public Rational ()
{ /* implementation not shown */ }
/** constructs a Rational with numerator n
* and denominator 1. */
public Rational (int n)
{ /* implementation not shown */ }
/** constructs a Rational with specified numerator
* and denominator . */
public Rational (int numer , int denom )
{ /* implementation not shown */ }
/** Returns numerator */
int numerator ()
{ /* implementation not shown */ }
/** Returns denominator */
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int denominator ()
{ /* implementation not shown */ }
/** Returns (this + r). Leaves this unchanged . */
public Rational plus ( Rational r)
{ /* implementation not shown */ }
// Similarly for times , minus , divide
...
/** Ensures denominator > 0. */
private void fixSigns ()
{ /* implementation not shown */ }
/** Ensures lowest terms. */
private void reduce ()
{ /* implementation not shown */ }
}
14. The method reduce() is not a public method because
A. methods whose return type is void cannot be public.
B. methods that change this cannot be public.
C. the reduce() method is not intended for use by objects outside the Rational
class.
D. the reduce() method is intended for use only by objects outside the Rational
class.
E. the reduce() method uses only the private data fields of the Rational
class.
15. The constructors in the Rational class allow initialization of Rational objects in
several different ways. Which of the following will cause an error?
A. Rational r1 = new Rational ();
B. Rational r2 = r1;
C. Rational r3 = new Rational (2 , -3);
D. Rational r4 = new Rational (3.5) ;
E. Rational r5 = new Rational (10) ;
16. Here is the implementation code for the plus method:
/** Returns (this + r). Leaves this unchanged . */
public Rational plus ( Rational r)
{
fixSigns ();
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r. fixSigns () ;
int denom = denominator * r. denominator ;
int numer = numerator * r. denominator
+ r. numerator * denominator ;
/* more code */
}
Which of the following is a correct replacement for /* more code */?
A. Rational rat ( numer , denom );
rat . reduce ();
return rat ;
B. return new Rational ( numer , denom );
C. reduce ()
Rational rat = new Rational ( number , denom );
return rat ;
D. Rational rat = new Rational ( numer , denom );
Rational . reduce ();
return rat ;
E. Rational rat = new Rational ( numer , denom );
rat . reduce ()
return rat ;
17. Assume these declarations:
Rational a = new Rational ();
Rational r = new Rational ( numer , denom );
int n = value ;
// numer , denom , and value are valid integer values
Which of the following will cause a compile-time error?
A. r = a. plus (r);
B. a = r. plus (new Rational (n));
C. r = r. plus (r);
D. a = n. plus (r);
E. r = r. plus (new Rational (n));
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Questions 18–20 refer to the Temperature class shown below.
public class Temperature
{
private String scale ; // valid values are "F" or "C"
private double degrees ;
/** constructor with specified degrees and scale */
public Temperature ( double tempDegrees , String tempScale )
{ /* implementation not shown */ }
/** Mutator .
* Converts this Temperature to degrees Fahrenheit .
* Returns this temperature in degree Fahrenheit .
* Precondition : Temperature is a valid temperature
* in degree Celsius .
*/
public Temperature toFahrenheit ()
{ /* implementation not shown */ }
/** Mutator .
* Converts this Temperature to degrees Celsius .
* Returns this temperature in degree Celsius .
* Precondition : Temperature is a valid temperature
* in degree Fahrenheit .
*/
public Temperature toCelsius ()
{ /* implementation not shown */ }
/** Mutator .
* Returns this temperature raised by amt degrees .
*/
public Temperature raise ( double amt )
{ /* implementation not shown */ }
/** Mutator .
* Returns this temperature lowered by amt degrees .
*/
public Temperature lower ( double amt )
{ /* implementation not shown */ }
/** Returns true if tempDegrees is a valid temperature
* in the given temperature scale , false otherwise .
*/
public static boolean isValidTemp ( double tempDegrees ,
String tempScale )
{ /* implementation not shown */ }
// Other methods are not shown.
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}
18. A client method contains this code segment:
Temperature t1 = new Temperature (40 , "C");
Temperature t2 = t1;
Temperature t3 = t2. lower (20) ;
Temperature t4 = t1. toFahrenheit ();
Which statement is true following execution of this segment?
A. t1, t2, t3, and t4 all represent the identical temperature, in degrees Celsius.
B. t1, t2, t3, and t4 all represent the identical temperature, in degrees Fahren-
heit.
C. t4 represents a Fahrenheit temperature, while t1, t2, and t3 all represent
degrees Celsius.
D. t1 and t2 refer to the same Temperature object; t3 refers to a Temperature
object that is 20 degrees lower than t1 and t2, while t4 refers to an object
that is t1 converted to Fahrenheit.
E. A NullPointerException was thrown.
19. Consider the following code.
public class TempTest
{
public static void main ( String [] args )
{
System . out . println (" Enter temperature scale :");
String tempScale = ...; // read user input
System . out . println (" Enter number of degrees :");
double tempDegrees = ...; // read user input
/* code to construct a valid temperature from user
input */
}
}
Which is the best replacement for /* code to construct… */?
A. Temperature t = new Temperature ( tempDegrees ,
tempScale );
B. Temperature t = new Temperature ( tempDegrees ,
tempScale );
if ( Temperature . isNotValidTemp ( tempDegrees ,
tempScale ))
/* error message and exit program */
C. Temperature t = new Temperature ( tempDegrees ,
tempScale );
if (!t. isValidTemp ( tempDegrees , tempScale ))
/* error message and exit program */
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D. if ( isValidTemp ( tempDegrees , tempScale ))
Temperature t = new Temperature ( tempDegrees ,
tempScale );
else
/* error message and exit program */
E. if ( Temperature . isValidTemp ( tempDegrees ,
tempScale ))
Temperature t = new Temperature ( tempDegrees ,
tempScale );
else
/* error message and exit program */
20. The formula to convert degrees Celsius C to Fahrenheit F is
F = 1.8C + 32
For example, 30° C is equivalent to 86° F.
An inFahrenheit() accessor method is added to the Temperature class. Here is its
implementation:
/** Returns an equivalent temperature in degrees Fahrenheit .
* Precondition : The temperature is a valid temperature
* in degree Celsius .
* Postcondition :
* - An equivalent temperature in degrees Fahrenheit has
* been returned .
* - Original temperature remains unchanged .
*/
public Temperature inFahrenheit ()
{
Temperature result ;
/* more code */
return result ;
}
Which of the following correctly replaces /* more code */ so that the postcondition
is achieved?
I. result = new Temperature ( degrees * 1.8 + 32 , "F");
II. result = new Temperature ( degrees * 1.8 , "F");
result = result . raise (32) ;
III. degrees *= 1.8;
this = this . raise (32) ;
result = new Temperature ( degrees , "F");
A. I only
B. II only
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C. III only
D. I and II only
E. I, II and III
21. Consider this program.
public class CountStuff
{
public static void doSomething ()
{
int count = 0;
...
// code to do something - no screen output produced
count ++;
}
public static void main ( String [] args )
{
int count = 0;
System . out . println (" How many iterations ?");
int n = ...; // read user input
for (int i = 1; i <= n; i ++)
{
doSomething ();
System . out . println ( count );
}
}
}
If the input value for n is 3, what screen output will this program subsequently
produce
A. 0
0
0
B. 0
1
2
C. 3
3
3
D. 3
?
?
where ? is some undefined value .
E. No output will be produced.
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22. This question refers to the following class.
public class IntObject
{
private int num ;
public IntObject () // constructor
{ num = 0; }
public IntObject (int n) // constructor
{ num = n; }
public void increment () // increment by 1
{ num ++; }
}
Here is a client program that uses this class:
public class IntObjectTest
{
public static IntObject someMethod ( IntObject obj )
{
IntObject ans = obj ;
ans . increment ();
return ans ;
}
public static void main ( String [] args )
{
IntObject x = new IntObject (2) ;
IntObject y = new IntObject (7) ;
IntObject a = y;
x = someMethod (y);
a = someMethod (x);
}
}
Just before exiting this program, what are the object values of x, y, and a, respec-
tively?
A. 9, 9, 9
B. 2, 9, 9
C. 2, 8, 9
D. 3, 8, 9
E. 7, 8, 9
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23. Consider the following program.
public class Tester
{
public void someMethod (int a, int b)
{
int temp = a;
a = b;
b = temp ;
}
}
public class TesterMain
{
public static void main ( Stirng [] args )
{
int x= 6, y = 8;
Tester tester = new Tester ();
tester . someMethod (x, y);
}
}
Just before the end of execution of this program, what are the values of x, y, and
temp, respectively?
A. 6, 8, 6
B. 8, 6, 6
C. 6, 8, ?, where ? means undefined
D. 8, 6, ?, where ? means undefined
E. 8, 6, 8
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