COMPS311F – Online Exam (Sample)
xx May 2020
Time Allowed: 2.5 hours (9:30 - 12:00)
Instructions:
- You should attempt ALL questions of the paper within the prescribed time.
- The total mark is worth 100 marks.
- Accept minor syntax errors.
- No need to include import statements.
- No need to handle exception except the questions are on exception or used as part of the
program logic.
- Submit a report containing answers to ALL the required questions. Your report must include
all the Java programs. Your report should be stored in a Word format (.doc or .docx).
Answers not included in your document file will not be marked.
- Put your name and student number on every page of your report.
- Name the document file in the format of COMPS311F-Exam-SXXXXXXX.doc (or .docx),
where XXXXXXX is your ID.
- Submit the document file to the “Take-home Exam” on the OLE (DO NOT put it in the
“Discussion Board”).
o
o “Multiple submission” is NOT allowed. It means that you can only submit your
answer file to the system once.
o You are strongly advised to try out the Trial Take-home Examination to familiarize
yourself with the submission process before the exam.
- You should click the “Save & Submit” button after your document file has been uploaded.
o
- Without specification, the submitted version on the “Take-home Exam” of the OLE will be
used for marking.
- Zero mark will be given for those who complete the submission after the prescribed time.
- Open book examination rules are applied. You are only allowed to use the internet to access
the OLE and the relevant Java API. You will be disqualified if you access to any shared
drives or social networking websites. Also, according to the regulation, cheating is
prohibited, includes but is not limited to “aiding or attempting to aid another candidate, or
obtaining or attempting to obtain aid from another candidate”.
Page 2 of 9
Question 1 [5 marks]
State whether each of the followings is true or false about Java:
(a) A protected method in a class cannot be overridden in a subclass.
(b) All variables are reference variables.
(c) A private attribute cannot be accessed anywhere.
(d) All methods must have at least one return statement.
(e) When a thread has successfully invoked a synchronized method of an object, no other
threads can invoke any of the methods of the object at the same time.
[5]
Question 2 [6 marks]
Write a class for a simple game. The game starts with generating two random integers. Then
the first who can give the sum of the two integers wins.
The class looks like this:
public class Game {
.....
public Game() {...}
syncrhonized public int[] getNumber() {...}
synchronized public boolean answer(int i) {...}
}
The constructor is to generate two random integers between 0 and 100 inclusive. The
getNumber method is for a player to get the two numbers. If someone has already given the
correct answer, then null will be returned. The answer method is used by a player to give
the answer. It will return true if no one else has provided the true answer and the answer
provided by the player is correct.
[6]
Question 3 [5 marks]
Write a program CountIntegers to read a number of files that contain only integers. The
integers have been written to the files using writeInt of DataOutputStream. You need
to use a separate thread to read in one file. Then, you need to write out the number of integers in
each file in ascending order.
For example, after executing the command:
java CountIntegers file1 file2 file3
May generate the output:
file3 has 256 integers
file2 has 345 integers
file1 has 1024 integers
Note that you need a data structure to store the numbers of integers in the files. The thread
which finished last is responsible for sorting and outputting the result.
[5]
Page 3 of 9
Question 4 [6 marks]
(a) In a static scoping language, when a subprogram encounters a non-local variable, where should
this be found?
[1]
(b) Consider the following Pascal code:
program A;
var a1:integer;
procedure E; forward;
procedure B;
var b1:integer;
procedure C;
var c1: integer;
begin {C begins}
......
end; {C ends}
procedure D;
var d1:integer;
begin {D begins}
......
end; {D ends}
begin {B begins}
......
end; {B ends}
procedure E;
var e1:integer;
begin {E begins}
......
end; {E ends}
begin {A begins}
......
end. {A ends}
Write the ARI records in the stack when the following procedure calls are made:
- Program A calls procedure B
- Procedure B calls procedure D
- Procedure D calls procedure E
- Procedure E calls procedure B
[5]
Question 5 [5 marks]
Write a Java class which models some online resources. The resources can only be used by at
most three users at a time. The resources are represented as the Java class Resource which has
been defined elsewhere. Now, you need to implement the class that control the use of the
resource:
Page 4 of 9
public class ControlResources {
private Resource resources[]=new Resource[3]; // the three
instances of resource
...
synchronized public Resource get(boolean waitToGet) {.....}
synchronized public void returnResource(Resource res) {....}
}
The get() is invoked by a user who wants to get a resource. It accepts a boolean parameter. If
the parameter is true, then the user will wait if at the moment no resource is available. If the
parameter is false, then the user does not want to wait. In this case, if there is no available
resource, the method will just return null. The returnResource() method is used for a
user to return a resource to the ControlResources object. You can assume that only those
users who have got a resource from the object will call this method to return it.
[5]
Question 6 [5 marks]
A database contains information regarding students and courses studied in a university.
Student (Information of students)
Attribute Data type
Name varchar(50)
StudentID varchar(10)
Address varchar(100)
Study (Study records of students)
Attribute Data type
StudentID varchar(10)
CourseID varchar(10)
Grade varchar(2)
Course (Information of courses)
Attribute Data type
CourseID varchar(10)
Title varchar(50)
Complete the following JSP that displays the student who failed a particular course (Grade F).
The id of the course should have been passed as the parameter named courseid.
<%
Class.forName("com.mysql.jdbc.Driver");
String url = "jdbc:mysql://192.168.62.100:3306/2014exam";
Connection con = DriverManager.getConnection(url,
"comps311f3", "comps311f3");
%>






<%
Page 5 of 9
// Add code here
%>



The following example shows the content when the request URL is:
http://plbpc001.ouhk.edu.hk/jsp/get.jsp?courseid=comps311
Only 3 students have failed this course. The title of the course is “Java Application
Development”.
[5]
Question 7 [5 marks]
(a) List one advantage and one disadvantage of passing parameters by value.
[2]
(b) Consider the following C like code:
#include
int a=3;
int b=4;
void fun(int x, int y) {
a=2*x;
x=y/2;
y=a;
}
void main() {
fun(b,b);
printf("%d %d\n",a,b);
}
What is the output of the program if the parameter passing method is:
(i) Pass-by-value.
(ii) Pass-by-value-result.
(iii) Pass by reference.
[3]
Page 6 of 9
Question 8 [6 marks]
Consider the following xml file:



David Au
Park Kiu



Ma Ko


In each , there are a number of s. can be empty. In ,
there must be one