Programming语言程序代做、代写java编程设计

日期：2021-03-08 10:31

Informatics 1: Object Oriented Programming

Assignment 2 – Understanding and reviewing code

Overview

This assignment is designed to give you experience in reading and understanding code that is not

your own. In so doing, you should learn to value well written code and gain an appreciation for

documentation. You are set three tasks, described in the Basic, Intermediate and Advanced sections

below. All your answers will be written up in the form of a report.

Basic: From code back to the specification

Usually, you are asked to write code to a given specification. Doing so can be seen as translating a

natural language to a programming language. The translation process is prone to error and requires

a lot of attention to detail. Once you have a prototype solution, it is useful to check that it does

exactly what it was supposed to. One way of spotting disparities between what the code actually

does and what was intended, is to have the programmer describe the program in their own words.

Comparing this to the initial specification can reveal important differences. Your first task is to

write such as a reverse translation i.e. work out the specification to which the given code appears to

have been written.

Step 1: Download the code

The program to be analysed is called PrecipitationGraph and is included in Assignment2.zip, which

can be downloaded from LEARN (under Assessment → Assignment 2).

Step 2: Get an overview of the code

Look at the different classes and their methods to gain an overview of the largest components that

make up the program. Initially, focus only on the names of the methods and any comments

describing what they do. At this stage, it can be counterproductive to read the code in the body of

methods or comments pertaining to individual lines of code.

Step 3: Run the code

The class Test.java contains the main method, which exercises some of the features of the program.

You can run this without having to edit the code. You may want to experiment a bit more by calling

other methods or changing parameters. In so doing, you might break the code, which is deliberately

imperfect. Take note of any errors you find for the intermediate task if you are attempting it.

Marks will be awarded out of 100 and count for 20% of your overall grade for Inf1B. Each 20 credit

course is designed to involve around 200 hours of work. Of those, 9 hours have been allotted for

this assignment. Completion time may vary depending on your level of experience and the grade

you are aiming for. Details on marking criteria can be found in the eponymous section below.

Step 4: Look at the details of the implementation

Now it is time to get your hands dirty and dive into the code itself. Your aim should be to extract

implementation details. Beware of errors in the code! If you find something that looks wrong, try to

work out the programmer’s intention even if a feature was not implemented correctly. Take notes

while you are doing this, but do not correct any errors in the code.

Step 5: Make a list of the program’s features

Use your notes and overall understanding of the program to compose a list of features that you think

the programmer was trying to provide (whether they succeeded or not). Include this in your report

in the form of short, technical bullet points. You can can assume the reader will be a programmer.

This should not be a description of the implementation however. Another developer may want to

follow a different approach, so state what the program should be able to do rather than how features

should be implemented.

Step 6: Write a specification

Finally, write a matching program specification. This is essentially a prose version of the features,

but it should be less technical. Imagine you are commissioning this piece of software and have

never seen a single line of code. To make sure the programmers you are hiring produce something

useful, you need to provide a detailed, unambiguous description of your requirements.

Step 7: Go beyond the code

Since you are reverse engineering the specification from the code, you can only see the features that

are provided. The absence of some features may, however, be conspicuous. Try to come up with two

additional features the company may require and explain why these would be useful in your report.

A template for the report is provided. See the ReportTemplate folder in Assignment2.zip.

Intermediate: Code review

Now that you have a specification, you can evaluate the provided code against it. Your job is to

write a code review. This involves developers going over code written by other members of their

team with the aim of finding errors and suggesting improvements. Your feedback should provide the

creator of PrecipitationGraph with practical advice on how to improve their implementation.

You will be marked on the quality of your code review, which should be:

? Complete – cover all issues you can find

? Specific – focus on parts of the code that need to be improved, avoid giving vague feedback

? Constructive – propose actionable steps to improve the code

? Justified – provide explanations and give reasons for why a proposed change is beneficial

The following outlines the aspects to be covered in the code review. Please use a tabular format in

your report as shown in the template. You can format the table differently if you wish, but there

must be a clear separation between different issues.

Functional correctness

Evaluate the extent to which the program fulfils the specification (not including the requirements

you added in step 7). Explain any issues you find and provide ideas for how to solve them. This is

not asking you to find ways of crashing the program – that is more often an issue with robustness

(to be reported under code quality below). Instead, you are looking for errors in the logic or cases in

which the program does something different to what it was meant to do.

Code quality

List up to ten different issues you can find with the quality of the code. Explain why the code needs

to be improved and make a suggestion for how to do so. If you find the same type of issue multiple

times, only report one instance of it (preferably the worst offence).

Desirable qualities include, but are not limited to:

? Structure

? A good design should split the task into more manageable chunks (think divide and conquer)

e.g. by a meaningful division of the code into classes.

? Modularity and reusability: Classes and methods perform well defined tasks. They can be

seen as building blocks for solving many different problems, not just the task at hand. Long

methods are a symptom of a too problem-specific design.

? Code duplication is avoided.

? Extensibility: New features can be added without redesigning the whole program.

? Robustness

? The program is able to handle errors and invalid/unexpected inputs without crashing.

? Correct use of access level modifiers (public/private) and static to restrict exposure.

? Technical/language proficiency

? Use the appropriate features of your programming language. This means not restricting

yourself to building everything using a few keywords when there is a more elegant solution.

It also means not using a needlessly complex mechanism for solving a simple task.

? Readability (self-documenting code)

? Use descriptive but concise names for variables, methods and classes.

? Class names start with a capital letter, method and variable names with a lower case letter.

? AllNamesAreWrittenInCamelCase

? Exception: Static constants are written in SHOUT_CASE.

? Use consistent formatting throughout all classes.

Code documentation

Give two example each of where:

? more comments would be helpful

? needless or uninformative comments clutter or obscure the code

? comments are actively misleading, distracting or inappropriate

Advanced: Legacy code

One of the developers on your team has gone into retirement and the job of maintaining their code

has been dumped on you. In order to add a new feature, you must understand how the existing code

works. The class X.java (in Assignment2.zip) is particularly obscure. Your predecessor seems to

have been obsessed with efficiency and has no concept of code quality or documentation. All you

can tell from context is that it must be some kind of data structure. You now have to look at the code

to work out what it does. Hint: Look up bitwise operators and bit shifting.

For each method in X.java, do the following:

? State what the method does.

? Give it a more descriptive name.

? Explain in detail how the code works (not required for methods m5 and m6).

Finally, answer the following questions:

? What kind of data structure is this and what would be a better class name?

? What are the advantages and disadvantages of the chosen data representation?

? Is there any justification for writing code like this (why/why not)?

Please note that attempting the more difficult tasks only removes grade capping. It does not

guarantee a mark in the corresponding range. Your answers are graded on how complete, accurate

and well presented they are. A good solution to one task is preferable to a poor attempt at all.

Report

A template for the report is provided, but you should still aim for the following qualities:

? Content

? Answer questions directly without beating about the bush.

? Do not just write down everything you know about the topic, stick to what was asked.

? Structure

? Break the content down into well labelled sections.

? If you are making an argument, ensure you organise your points into a logical sequence.

? Try to make the text flow by avoiding frequent or abrupt changes of topic.

? Writing style

? Should be clear and concise. Make the report as short as possible without cutting essential

details.

? Avoid repetition: Make your point once and make it well, but avoid re-stating it.

Solving the task described in the Basic section is sufficient to obtain a grade (up to 49%).

Both basic and intermediate tasks must be solved for a grade (up to 79%).

You will need to tackle all three tasks to get an A (up to 100%).