Week 2 [Aug 19] - Topics

The following description of the Joys of the Programming Craft was taken from Chapter 1 of the famous book The Mythical Man-Month, by Frederick P. Brooks.

Why is programming fun? What delights may its practitioner expect as his reward?

First is the sheer joy of making things. As the child delights in his mud pie, so the adult enjoys building things, especially things of his own design. I think this delight must be an image of God's delight in making things, a delight shown in the distinctness and newness of each leaf and each snowflake.

Second is the pleasure of making things that are useful to other people. Deep within, we want others to use our work and to find it helpful. In this respect the programming system is not essentially different from the child's first clay pencil holder "for Daddy's office."

Third is the fascination of fashioning complex puzzle-like objects of interlocking moving parts and watching them work in subtle cycles, playing out the consequences of principles built in from the beginning. The programmed computer has all the fascination of the pinball machine or the jukebox mechanism, carried to the ultimate.

Fourth is the joy of always learning, which springs from the nonrepeating nature of the task. In one way or another the problem is ever new, and its solver learns something: sometimes practical, sometimes theoretical, and sometimes both.

Finally, there is the delight of working in such a tractable medium. The programmer, like the poet, works only slightly removed from pure thought-stuff. He builds his castles in the air, from air, creating by the exertion of the imagination. Few media of creation are so flexible, so easy to polish and rework, so readily capable of realizing grand conceptual structures....

Yet the program construct, unlike the poet's words, is real in the sense that it moves and works, producing visible outputs separate from the construct itself. It prints results, draws pictures, produces sounds, moves arms. The magic of myth and legend has come true in our time. One types the correct incantation on a keyboard, and a display screen comes to life, showing things that never were nor could be.

Programming then is fun because it gratifies creative longings built deep within us and delights sensibilities we have in common with all men.

Not all is delight, however, and knowing the inherent woes makes it easier to bear them when they appear.

First, one must perform perfectly. The computer resembles the magic of legend in this respect, too. If one character, one pause, of the incantation is not strictly in proper form, the magic doesn't work. Human beings are not accustomed to being perfect, and few areas of human activity demand it. Adjusting to the requirement for perfection is, I think, the most difficult part of learning to program.

Next, other people set one's objectives, provide one's resources, and furnish one's information. One rarely controls the circumstances of his work, or even its goal. In management terms, one's authority is not sufficient for his responsibility. It seems that in all fields, however, the jobs where things get done never have formal authority commensurate with responsibility. In practice, actual (as opposed to formal) authority is acquired from the very momentum of accomplishment.

The dependence upon others has a particular case that is especially painful for the system programmer. He depends upon other people's programs. These are often maldesigned, poorly implemented, incompletely delivered (no source code or test cases), and poorly documented. So he must spend hours studying and fixing things that in an ideal world would be complete, available, and usable.

The next woe is that designing grand concepts is fun; finding nitty little bugs is just work. With any creative activity come dreary hours of tedious, painstaking labor, and programming is no exception.

Next, one finds that debugging has a linear convergence, or worse, where one somehow expects a quadratic sort of approach to the end. So testing drags on and on, the last difficult bugs taking more time to find than the first.

The last woe, and sometimes the last straw, is that the product over which one has labored so long appears to be obsolete upon (or before) completion. Already colleagues and competitors are in hot pursuit of new and better ideas. Already the displacement of one's thought-child is not only conceived, but scheduled.

This always seems worse than it really is. The new and better product is generally not available when one completes his own; it is only talked about. It, too, will require months of development. The real tiger is never a match for the paper one, unless actual use is wanted. Then the virtues of reality have a satisfaction all their own.

Of course the technological base on which one builds is always advancing. As soon as one freezes a design, it becomes obsolete in terms of its concepts. But implementation of real products demands phasing and quantizing. The obsolescence of an implementation must be measured against other existing implementations, not against unrealized concepts. The challenge and the mission are to find real solutions to real problems on actual schedules with available resources.

This then is programming, both a tar pit in which many efforts have floundered and a creative activity with joys and woes all its own. For many, the joys far outweigh the woes....

[Text and book cover source: Wikipedia]	[Fred Brooks photo source]

The Mythical Man-Month: Essays on Software Engineering is a book on software engineering and project management by Fred Brooks, whose central theme is that "adding manpower to a late software project makes it later". This idea is known as Brooks's law, and is presented along with the second-system effect and advocacy of prototyping.

Professional software engineers often write code using Integrated Development Environments (IDEs). IDEs support most development-related work within the same tool (hence, the term integrated).

An IDE generally consists of:

• A source code editor that includes features such as syntax coloring, auto-completion, easy code navigation, error highlighting, and code-snippet generation.
• A compiler and/or an interpreter (together with other build automation support) that facilitates the compilation/linking/running/deployment of a program.
• A debugger that allows the developer to execute the program one step at a time to observe the run-time behavior in order to locate bugs.
• Other tools that aid various aspects of coding e.g. support for automated testing, drag-and-drop construction of UI components, version management support, simulation of the target runtime platform, and modeling support.

Examples of popular IDEs:

• Java: Eclipse, Intellij IDEA, NetBeans
• C#, C++: Visual Studio
• Swift: XCode
• Python: PyCharm

Some Web-based IDEs have appeared in recent times too e.g., Amazon's Cloud9 IDE.

Some experienced developers, in particular those with a UNIX background, prefer lightweight yet powerful text editors with scripting capabilities (e.g. Emacs) over heavier IDEs.

Running Intellij IDEA for the First Time

Importing a Project to Intellij IDEA

When testing, we execute a set of test cases. A test case specifies how to perform a test. At a minimum, it specifies the input to the software under test (SUT) and the expected behavior.

Test cases can be determined based on the specification, reviewing similar existing systems, or comparing to the past behavior of the SUT.

For each test case we do the following:

1. Feed the input to the SUT
2. Observe the actual output
3. Compare actual output with the expected output

A test case failure is a mismatch between the expected behavior and the actual behavior. A failure indicates a potential defect (or a bug), unless the error is in the test case itself.

When we modify a system, the modification may result in some unintended and undesirable effects on the system. Such an effect is called a regression.

Regression testing is the re-testing of the software to detect regressions. Note that to detect regressions, we need to retest all related components, even if they had been tested before.

Regression testing is more effective when it is done frequently, after each small change. However, doing so can be prohibitively expensive if testing is done manually. Hence, regression testing is more practical when it is automated.

A simple way to semi-automate testing of a CLI(Command Line Interface) app is by using input/output re-direction.

• First, we feed the app with a sequence of test inputs that is stored in a file while redirecting the output to another file.
• Next, we compare the actual output file with another file containing the expected output.

Let us assume we are testing a CLI app called AddressBook. Here are the detailed steps:

1. Store the test input in the text file input.txt.

   add Valid Name p/12345 valid@email.butNoPrefix
   add Valid Name 12345 e/valid@email.butPhonePrefixMissing
   

2. Store the output we expect from the SUT in another text file expected.txt.

   Command: || [add Valid Name p/12345 valid@email.butNoPrefix]
   Invalid command format: add 
   
   Command: || [add Valid Name 12345 e/valid@email.butPhonePrefixMissing]
   Invalid command format: add 
   

3. Run the program as given below, which will redirect the text in input.txt as the input to AddressBook and similarly, will redirect the output of AddressBook to a text file output.txt. Note that this does not require any code changes to AddressBook.

   java AddressBook < input.txt > output.txt
   

   • The way to run a CLI program differs based on the language.
     e.g., In Python, assuming the code is in AddressBook.py file, use the command
     python AddressBook.py < input.txt > output.txt

   • If you are using Windows, use a normal command window to run the app, not a Power Shell window.

   More on the > operator and the < operator extra

   A CLI program takes input from the keyboard and outputs to the console. That is because those two are default input and output streams, respectively. But you can change that behavior using < and > operators. For example, if you run AddressBook in a command window, the output will be shown in the console, but if you run it like this,

   java AddressBook > output.txt 
   

   the Operating System then creates a file output.txt and stores the output in that file instead of displaying it in the console. No file I/O coding is required. Similarly, adding < input.txt (or any other filename) makes the OS redirect the contents of the file as input to the program, as if the user typed the content of the file one line at a time.

   Resources:

   • Using command redirection operators in Windows

4. Next, we compare output.txt with the expected.txt. This can be done using a utility such as Windows FC (i.e. File Compare) command, Unix diff command, or a GUI tool such as WinMerge.

   FC output.txt expected.txt
   

Note that the above technique is only suitable when testing CLI apps, and only if the exact output can be predetermined. If the output varies from one run to the other (e.g. it contains a time stamp), this technique will not work. In those cases we need more sophisticated ways of automating tests.

Revision control software are also known as Version Control Software (VCS), and by a few other names.

Install SourceTree which is Git + a GUI for Git. If you prefer to use Git via the command line (i.e., without a GUI), you can install Git instead.

Suppose you want to create a repository in an empty directory things. Here are the steps:

Windows: Click File → Clone/New…. Click on Create button.
Mac: New... → Create New Repository.

Enter the location of the directory (Windows version shown below) and click Create.

Go to the things folder and observe how a hidden folder .git has been created.

Note: If you are on Windows, you might have to configure Windows Explorer to show hidden files.

Open a Git Bash Terminal.

If you installed SourceTree, you can click the Terminal button to open a GitBash terminal.

Navigate to the things directory.

Use the command git init which should initialize the repo.

$ git init
Initialized empty Git repository in c:/repos/things/.git/

You can use the command ls -a to view all files, which should show the .git directory that was created by the previous command.

$ ls -a
.  ..  .git

You can also use the git status command to check the status of the newly-created repo. It should respond with something like the bellow

git status

# On branch master
#
# Initial commit
#
nothing to commit (create/copy files and use "git add" to track)

Tracking and Ignoring

In a repo, we can specify which files to track and which files to ignore. Some files such as temporary log files created during the build/test process should not be revision-controlled.

Staging and Committing

Identifying Points in History

Each commit in a repo is a recorded point in the history of the project that is uniquely identified by an auto-generated hash e.g. a16043703f28e5b3dab95915f5c5e5bf4fdc5fc1.

We can tag a specific commit with a more easily identifiable name e.g. v1.0.2

Create an empty repo.

Create a file named fruits.txt in the working directory and add some dummy text to it.

Observe how the file is detected by Git.

The file is shown as ‘unstaged’

You can use the git status command to check the status of the working directory.

git status

# On branch master
#
# Initial commit
#
# Untracked files:
#   (use "git add <file>..." to include in what will be committed)
#
#   a.txt
nothing added to commit but untracked files present (use "git add" to track)

Although git has detected the file in the working directory, it will not do anything with the file unless you tell it to. Suppose we want to commit the current state of the file. First, we should stage the file.

Select the fruits.txt and click on the Stage Selected button

fruits.txt should appear in the Staged files panel now.

You can use the stage or the add command (they are synonyms, add is the more popular choice) to stage files.

git add fruits.txt
git status

# On branch master
#
# Initial commit
#
# Changes to be committed:
#   (use "git rm --cached <file>..." to unstage)
#
#       new file:   fruits.txt
#

Now, you can commit the staged version of fruits.txt

Click the Commit button, enter a commit message e.g. add fruits.txt in to the text box, and click Commit

Use the commit command to commit. The -m switch is used to specify the commit message.

git commit -m "add fruits.txt"

You can use the log command to see the commit history

git log

commit 8fd30a6910efb28bb258cd01be93e481caeab846
Author: … < … @... >
Date:   Wed Jul 5 16:06:28 2017 +0800

  Add fruits.txt

Note the existence of something called the master branch. Git allows you to have multiple branches (i.e. it is a way to evolve the content in parallel) and Git creates a default branch named master on which the commits go on by default.

Do some changes to fruits.txt (e.g. add some text and delete some text). Stage the changes, and commit the changes using the same steps you followed before. You should end up with something like this.

Next, add two more files colors.txt and shapes.txt to the same working directory. Add a third commit to record the current state of the working directory.

Add a file named temp.txt to the things repo you created. Suppose we don’t want this file to be revision controlled by Git. Let’s instruct Git to ignore temp.txt

temp.txt

temp.txt

The .gitignore file tells Git which files to ignore when tracking revision history. That file itself can be either revision controlled or ignored.

• To version control it (the more common choice – which allows you to track how the .gitignore file changed over time), simply commit it as you would commit any other file.
• To ignore it, follow the same steps we followed above when we set Git to ignore the temp.txt file.

RCS tools store the history of the working directory as a series of commits. This means we should commit after each change that we want the RCS to 'remember' for us.

To see what changed between two points of the history, you can ask the RCS tool to diff the two commits in concern.

To restore the state of the working directory at a point in the past, you can checkout the commit in concern. i.e., we can traverse the history of the working directory simply by checking out the commits we are interested in.

Let's tag a commit in a local repo you have (e.g. the sampelrepo-things repo)

Right-click on the commit (in the graphical revision graph) you want to tag and choose Tag…

Specify the tag name e.g. v1.0 and click Add Tag.

The added tag will appear in the revision graph view.

To add a tag to the current commit as v1.0,

git tag –a v1.0

To view tags

git tag

To learn how to add a tag to a past commit, go to the ‘Git Basics – Tagging’ page of the git-scm book and refer the ‘Tagging Later’ section.

Remember to push tags to the repo. A normal push does not include tags.

# push a specific tag
git push origin v1.0b

# push all tags
git push origin --tags

Git can show you what changed in each commit.

To see which files changed in a commit, click on the commit. To see what changed in a specific file in that commit, click on the file name.

git show < part-of-commit-hash >

Example:

git show 251b4cf

commit 5bc0e30635a754908dbdd3d2d833756cc4b52ef3
Author: … < … >
Date:   Sat Jul 8 16:50:27 2017 +0800

    fruits.txt: replace banana with berries

diff --git a/fruits.txt b/fruits.txt
index 15b57f7..17f4528 100644
--- a/fruits.txt
+++ b/fruits.txt
@@ -1,3 +1,3 @@
 apples
-bananas
+berries
 cherries

Git can also show you the difference between two points in the history of the repo.

Select the two points you want to compare using Ctrl+Click.

The same method can be used to compare the current state of the working directory (which might have uncommitted changes) to a point in the history.

The diff command can be used to view the differences between two points of the history.

• git diff : shows the changes (uncommitted) since the last commit
• git diff 0023cdd..fcd6199: shows the changes between the points indicated by by commit hashes
• git diff v1.0..HEAD: shows changes that happened from the commit tagged as v1.0 to the most recent commit.

• Git-Tower Tutorial: Inspecting Changes with Diffs
• How to view the next page of a git command result

Git can load a specific version of the history to the working directory. Note that if you have uncommitted changes in the working directory, you need to stash them first to prevent them from being overwritten.

Double-click the commit you want to load to the working directory, or right-click on that commit and choose Checkout....

Click OK to the warning about ‘detached HEAD’ (similar to below).

The specified version is now loaded to the working folder, as indicated by the HEAD label. HEAD is a reference to the currently checked out commit.

If you checkout a commit that come before the commit in which you added the .gitignore file, Git will now show ignored fiels as ‘unstaged modifications’ because at that stage Git hasn’t been told to ignore those files.

To go back to the latest commit, double-click it.

Use the checkout <commit-identifier> command to change the working directory to the state it was in at a specific past commit.

• git checkout v1.0: loads the state as at commit tagged v1.0
• git checkout 0023cdd: loads the state as at commit with the hash 0023cdd
• git checkout HEAD~2: loads the state that is 2 commits behind the most recent commit

For now, you can ignore the warning about ‘detached HEAD’.

Use the checkout <branch-name> to go back to the most recent commit of the current branch (the default branch in git is named master)

• git checkout master

You can use the git's stash feature to temporarily shelve (or stash) changes you've made to your working copy so that you can work on something else, and then come back and re-apply the stashed changes later on. _{-- adapted from this}

Remote repositories are copies of a repo that are hosted on remote computers. They are especially useful for sharing the revision history of a codebase among team members of a multi-person project. They can also serve as a remote backup of your code base.

You can clone a remote repo onto your computer which will create a copy of a remote repo on your computer, including the version history as the remote repo.

You can push new commits in your clone to the remote repo which will copy the new commits onto the remote repo. Note that pushing to a remote repo requires you to have write-access to it.

You can pull from the remote repos to receive new commits in the remote repo. Pulling is used to sync your local repo with latest changes to the remote repo.

While it is possible to set up your own remote repo on a server, an easier option is to use a remote repo hosting service such as GitHub or BitBucket.

A fork is a remote copy of a remote repo. If there is a remote repo that you want to push to but you do not have write access to it, you can fork the remote repo, which gives you your own remote repo that you can push to.

A pull request is mechanism for contributing code to a remote repo. It is a formal request sent to the maintainers of the repo asking them to pull your new code to their repo.

Clone the sample repo samplerepo-things to your computer.

Clone the sample repo as explained in [Textbook Tools → Git & GitHub → Clone].

Delete the last two commits to simulate cloning the repo 2 commits ago.

Right-click the target commit (i.e. the commit that is 2 commits behind the tip) and choose Reset current branch to this commit.

Choose the Hard - … option and click OK.

This is what you will see.

Note the following (cross refer the screenshot above):

Arrow marked as a: The local repo is now at this commit, marked by the master label.
Arrow marked as b: origin/master label shows what is the latest commit in the master branch in the remote repo.

Use the reset command to delete commits at the tip of the revision history.

git reset --hard HEAD~2

Now, your local repo state is exactly how it would be if you had cloned the repo 2 commits ago, as if somebody has added two more commits to the remote repo since you cloned it. To get those commits to your local repo (i.e. to sync your local repo with upstream repo) you can do a pull.

Click the Pull button in the main menu, choose origin and master in the next dialog, and click OK.

Now you should see something like this where master and origin/master are both pointing the same commit.

git pull origin

1. Create a GitHub account if you don't have one yet.

2. Fork the samplerepo-things to your GitHub account:

   Navigate to the on GitHub and click on the button on the top-right corner.

3. Clone the fork (not the original) to your computer.

4. Create some commits in your repo.

5. Push the new commits to your fork on GitHub

Click the Push button on the main menu, ensure the settings are as follows in the next dialog, and click the Push button on the dialog.

Tags are not included in a normal push. Remember to tick Push all tags when pushing to the remote repo if you want them to be pushed to the repo.

Use the command git push origin master. Enter Github username and password when prompted.

Tags are not included in a normal push. To push a tag, use this command: git push origin <tag_name> e.g.. git push origin v1.0