Lab 2: Simulation 2

• Deadline: 7 February 2023, Tuesday, 23:59 SST
• Marks: 12
• Weightage: 3%

Prerequisite:

• Completed Lab 1
• Caught up to Unit 19 of Lecture Notes
• Familiar with CS2030S Java style guide
• Revised the CS2030S Lab guide

Reminder: Only use the submit and get scripts. Do not use any git commands.

Goal

This is a continuation of Lab 1. Lab 2 changes some of the requirements of Lab 1 and adds some new things to the world that we are simulating. The goal is to demonstrate that, when OO-principles are applied properly, we can adapt our code to changes in the requirement with less effort.

Lab 2 also nudges you towards following good coding practice by adhering to a published coding convention.

Simulating a Bank with a Queue

Recall that, no waiting was allowed inside the bank we are simulating. The bank is losing customers as a customer departs if all the counters are busy.

Lab 2 adds an entrance queue to the bank. If all counters are busy when a customer arrives, the customer will join the queue and wait. When a counter becomes available, the customer at the front of the queue will proceed to the counter for service.

The entrance queue has a maximum queue length of \(m\). If there are already \(m\) customers waiting in the entrance queue, any arriving customer will be turned away.

Building on Lab 1

You are required to build on top of your Lab 1 submission for this lab.

Assuming you have lab1-<username> and lab2-<username> under the same directory, and lab2-<username> is your current working directory, you can run

cp -i ../lab1-<username>/*.java .
rm -i Lab1.java

to copy all your Java code over.

If you are still unfamiliar with Unix commands to navigate the file system and processing files, please review our Unix guide.

You are encouraged to consider your tutor's feedback and fix any issues with your design for your Lab 1 submission before you embark on your Lab 2.

Skeleton for Lab 2

We only provide two classes for Lab 2, the main Lab2.java (which is simply Lab1.java renamed) and Queue.java.

Both files should not be modified for this lab.

The Queue class

Queue is a general class for a first-in, first-out queue of objects. Here is an example of how it is used:

// Create a queue that holds up to 4 elements
Queue q = new Queue(4);

// Add a string into the queue.  returns true if successful; 
// false otherwise.
boolean b = q.enq("a1");

// Remove a string from the queue.  `Queue::deq` returns an 
// `Object`, so narrowing type conversion is needed.  Returns 
// `null` is queue is empty.
String s = (String) q.deq();

// Returns the string representation of the queue (showing 
// each element)
String s = q.toString();

// Returns true if the queue is full, false otherwise.
boolean b = q.isFull();

// Returns true if the queue is empty, false otherwise.
boolean b = q.isEmpty();

// Returns the number of objects in the queue
int l = q.length();

Other Changes Needed

In addition to adding an entrance queue to the bank, we need to make the following changes to the input and output of the program.

1. There is an additional input parameter in the first line of the input file, an integer \(m\), indicating the maximum allowed length of the entrance queue. This input parameter should be read immediately after reading the number of customers and the number of service counters.

2. Customers now come to the bank with a task they intend to do, either to deposit or withdrawal. As such, there is an additional input parameter for each customer arrival, an int which is either \(0\) for deposit or \(1\) for withdrawal.

3. A customer will now be printed with a single letter prefix C. For instance, instead of Customer 1, we print C1.

4. A service counter will now be printed with a single letter prefix S. For instance, instead of Counter 1, we print S1.

5. The entrance queue of the bank will be printed with the arrival event. E.g., the following shows that C3 arrived at time 1.400 and at the time of arrival, there are two customers, C1 and C2, waiting in the entrance queue.

   1.400: C3 arrived [ C1 C2 ]
   

6. If a customer joins the entrance queue, the customer along with the queue before joining should be printed. E.g.,

   1.400: C3 joined queue [ C1 C2 ]
   

7. When a customer begins being served or is done being served, the task the customer is doing should be printed. For example, Customer C2 withdrawing at bank counter S1 would be printed as:

   5.100: C2 Withdrawal begin (by S0)
   7.100: C2 Withdrawal done (by S0)
   

Note: we are not going to implement the withdrawal and deposit logic in our bank simulator yet.

Following CS2030S Style Guide

In addition to the changes above, you should also make sure that your code follows the given Java style guide

Assumptions

We assume that no two events involving two different customers ever occur at the same time (except when a customer departs and another customer begins its service). As per all labs, we assume that the input is correctly formatted.

Your Task

Your task for this lab is to (i) improve upon your design for Lab 1 if needed, (ii) update BankSimulation and associated classes to simulate the entrance queue, (iii) update the input and output components of the classes to conform to the specification above.

If the design for Lab 1 follows the OOP principles, then only about 50 lines of changes/additions are required.

Compiling, Testing, and Debugging

Compilation

To compile your code,

javac *.java

Running and Testing

You should not test your code by manually entering the inputs. Instead, enter the inputs into a file, and run

java Lab2 < file

A set of test inputs is provided as part of the skeleton, named Lab2.x.in under the inputs directory. You can run them with, for instance,

java Lab2 < inputs/Lab2.1.in

You can save the output by redirecting it into a file.

java Lab2 < inputs/Lab2.1.in > OUT

You can automatically test your code against all the given inputs/outputs as well as against the checkstyle by running:

./test.sh Lab2

Debugging

The expected outputs are given in the outputs directory. You can compare OUT with the expected output with diff or vim. Using vim,

vim -d OUT output/Lab2.1.out

will open both files and highlight the differences.

As the output becomes too long, you can focus on tracing a particular counter or customer with the help of grep. Suppose you want to focus on what happened to Customer 1 in OUT, run

$ grep ": C1" OUT
1.200: C1 arrived [ ]
1.200: C1 service begin (by S1)
2.200: C1 service done (by S1)
2.200: C1 departed

Suppose you want to see all the customers served by S1, run:

$ grep "S1" OUT
1.200: C1 service begin (by S1)
2.200: C1 service done (by S1)
2.200: C4 service begin (by S1)
3.200: C4 service done (by S1)

Grading

This lab is worth 12 marks and contributes 3% to your final grade. The marking scheme is as follows:

• Style: 2 marks
• Correctness: 2 marks
• OO Principles: 8 marks

We may make additional deductions for other issues or errors in your code, such as compilation errors, bad practices, failure to follow instructions, etc.