COMP 132 Practice Midterm Exam I Solution 75 points name: 1. (12 ...

name:
COMP 132 Practice Midterm Exam I Solution
75 points
1. (12 points) Find and clearly explain at least three errors in the following program. The errors could
be compile time or runtime errors. Answers are at the top of the next page.
public interface Tasty {
int flavorLevel();
boolean tastierThan(Tasty t);
}
public class Pizza implements Tasty {
private boolean extraCheese;
public Pizza(boolean ec) { extraCheese = ec; }
public int flavorLevel() {
if (extraCheese) { return 10; } else { return 5; }
}
}
public boolean hasExtra() { return extraCheese; }
public class Anchovy {
private int salt;
public Anchovy(int initSalt) { salt = initSalt; }
public int flavorLevel() { return salt + 5; }
public int saltiness() { return salt; }
}
public boolean tastierThan(Tasty t) { return salt > t.saltiness(); }
public class Salad implements Tasty {
private String dressing;
}
public Salad(String initDressing) { dressing = initDressing; }
public int flavorLevel() { return dressing.length(); }
public boolean tastierThan(Tasty t) { return this.flavorLevel() > t.flavorLevel(); }
public static void main(String [] args) {
Tasty s = new Salad("Peppercorn Ranch");
Anchovy a = new Anchovy(30);
System.out.println(s.tastierThan(a));
Pizza p = (Pizza) s;
System.out.println(p.hasExtra());
}
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The Pizza class does not implement the tastierThan method, even though it implements the Tasty
interface.
In main, an instance of Anchovy is passed as a parameter to the tastierThan method, but Anchovy
does not implement the Tasty interface.
In main, an instance of Salad is cast to Pizza - this would cause a ClassCastException at runtime.
2. (5 points) Was the Minesweeper lab a good example of the Model-View-Controller design pattern If
so, which parts of the code were the model and which parts were the view If not, why not
Yes. The model is the MineSweeperBoard class because it maintains the state of the application and
does all computation. The view is the MineSweeper class because it defines the GUI for the application.
3. Suppose that class ExampleClass in package comp132.exam1 declares a field as follows:
public static final int TWO = 2;
State whether or not each of the following method definitions would compile (your answer for each
should just be yes or no):
(a) (2 points) Assume this method is in class ExampleClass in package comp132.exam1.
public void printFour() { System.out.println(TWO + 2); } Yes
(b) (2 points) Assume this method is in class ExampleClass in package comp132.exam1.
public void addTwo() { TWO = TWO + 2; } No
(c) (2 points) Assume this method is in class SampleClass in package comp132.examples.
public void printTwo() { System.out.println(comp132.exam1.ExampleClass.TWO); }Yes
4. (8 points) What output is displayed by the following code snippet
int [] [] mat = new int [4][4];
for (int i = 0; i < mat.length; i++) {
for (int j = 0; j < mat[0].length; j++) {
mat[i][j] = (i + 1) * (j + 1);
}
}
int j = mat[0].length - 1;
for (int i = 0; i < mat.length; i++) {
System.out.println(mat[i][j]);
j = j - 1;
}
5. (5 points) Suppose that a program crashes because a method is called when its precondition is not
satisfied. Is this the fault of the programmer who wrote the method, or of the programmer who wrote
the code that called the method Why
The programmer who wrote the code that called the method. The precondition is a contract between the
method and calling code, and a method is only guaranteed to work correctly when its precondition is
satisfied. Hence, the second programmer broke the contract by calling the method when its precondition
was not satisfied.
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6
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6. (39 points) The following definition of class Employee will be used for storing information about the
employees of a large company. Complete the definition of the equals method according to the given
javadoc specification.
public class Employee {
private String name;
private int yearHired;
private int salary;
public String getName() { return name; }
public int getYearHired() { return yearHired; }
public int getSalary() { return salary; }
public Employee(String initName, int initYear, int initSalary) {
name = initName;
yearHired = initYear;
salary = initSalary;
}
public void giveRaise(int amount) {
salary = salary + amount;
/** @return whether or not obj is an employee with the same name, year hired and
salary as the calling object */
public boolean equals(Object obj) {
if (obj instanceof Employee) {
Employee emp = (Employee) obj;
return name.equals(emp.name) && salary == emp.salary
&& yearHired == emp.yearHired;
} else {
return false;
}
}
}
On the next page, complete the definition of the constructor and equals method for the Manager
class, which represents managers who work for the company. The constructor must initialize all fields
(includingthoseinheritedfromEmployee),andyouarenotallowedtoaddanymethodstotheEmployee
class.
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public class Manager extends Employee {
private int numManagees; // the number of employees managed by this manager
public int getNumManaged() { return numManagees; }
/** initialize all fields of the manager with the specified parameters */
public Manager (String initName, int initYear, int initSalary, int numManaged) {
}
super(initName, initYear, initSalary);
numManagees = numManaged;
/** @return whether or not obj is a Manager with the same name, year hired, salary
and number of managees as the calling object. For full credit, do not use any
of the accessors from the Employee class (getName, getYearHired, getSalary in
your solution. */
public boolean equals(Object obj) {
if (super.equals(obj)) {
return obj instanceof Manager && ((Manager) obj).numManagees == numManagees;
} else {
return false;
}
}
}
Finally, complete the definitions of the hireEmployee, giveEmployeesRaise and managementReport
methods of the Payroll class (on the next page) according to the given javadoc specifications. Note
that the signature of the hireEmployee method is not given - you must provide the parameters and
return type for this method. If you need more space, you can use the back of the page as long as you
indicate that you have done so.
import java.util.ArrayList;
public class Payroll {
private ArrayList allEmployees;
public Payroll() {
allEmployees = new ArrayList();
}
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** the hireEmployee method can add both regular employees and Managers to the
payroll - define it here */
public void hireEmployee(Employee e) {
allEmployees.add(e);
}
/** increase the salary of all employees who are not managers by the
specified amount */
public void giveEmployeesRaise(int amount) {
}
for (Employee e : allEmployees) {
if (!(e instanceof Manager)) {
e.giveRaise(amount);
}
}
/** print the name of each manager and the number of employees that person manages */
public void managementReport() {
for (Employee e : allEmployees) {
if (e instanceof Manager) {
System.out.print(e.getName() + ": " + ((Manager) e).getNumManaged());
}
}
}
}
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