Week 2 [Mon, Aug 19th] - Topics

The following description of the Joys of the Programming Craft was taken (and emphasis added) 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, you want others to use your 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 you 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....

Software development goes through different stages such as requirements, analysis, design, implementation and testing. These stages are collectively known as the software development lifecycle (SDLC). There are several approaches, known as software development lifecycle models (also called software process models), that describe different ways to go through the SDLC. Each process model prescribes a 'roadmap' for the software developers to manage the development effort. The roadmap describes the aims of the development stages, the outcome of each stage, and the workflow i.e. the relationship between stages.

The sequential model, also called the waterfall model, views software development as a linear process, in which the project is seen as progressing through the development stages. The name waterfall stems from how the model is drawn to look like a waterfall (see below).

When one stage of the process is completed, it produces some artifacts to be used in the next stage. For example, the requirements stage produces a comprehensive list of requirements, to be used in the design phase.

A strict sequential model project moves only in the forward direction i.e., each stage is completed before starting the next. For example, once the requirements stage is over, there is no provision for revising the requirements later.

This model can work well for a project that produces software to solve a well-understood problem, in which case the requirements can remain stable and the effort can be estimated accurately. Furthermore, as each stage has a well-defined outcome, it is easy to track the progress of the project because one can gauge the project progress by monitoring which stage the project is in.

However, real-world projects often tackle problems that are not well-understood at the beginning, making them unsuitable for this model. For example, target users of a software product may not be able to state their requirements accurately at the start of the project, if they have not used a similar product before.

The iterative model advocates producing the software by going through several iterations. Each of the iterations could potentially go through all the stages of the SDLC, from requirements gathering to deployment.

Each iteration produces a new version of the product, building upon the version produced in the previous iteration. Feedback from each iteration is factored into the subsequent iterations. For example, if an implementation task took longer than expected, the effort estimate for a similar tasks in future iterations can be adjusted accordingly. Similarly, if a feature introduced in the current iteration was not well-received by target users, it can be removed or tweaked in the next iteration.

The iterative model can be done in breadth-first or depth-first approach.

• In the breadth-first approach, an iteration evolves all major components and all functionality areas in parallel i.e., most features and most will be updated in each iteration, producing a working product at the end of each iteration.
• In the depth-first approach, an iteration focuses on fleshing out only some components or some functionality area. Accordingly, early depth-first iterations might not produce a working product.

A project can be done as a mixture of breadth-first and depth-first iterations i.e., an iteration can contain some breadth-first work as well as some depth-first work, or, some iterations can be breadth-first while others are depth-first.

This book chapter assumes you are familiar with basic C++ programming. It provides a crash course to help you migrate from C++ to Java.

This chapter borrows heavily from the excellent book ThinkJava by Allen Downey and Chris Mayfield. As required by the terms of reuse of that book, this chapter is released under the Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License and not under the MIT license as the rest of this book.

Some conventions used in this chapter:

Other resources used:

• C++ and Java Syntax Differences Cheat Sheet by Alex Allain
• Java Tutorial provided by Oracle. Extracts from this resource are marked as -- Java Tutorial

Java was conceived by James Gosling and his team at Sun Microsystems in 1991.

Java is directly related to both C and C++. Java inherits its syntax from C. Its object model is adapted from C++. --Java: A Beginner’s Guide, by Oracle

Oracle became the owner of Java in 2010, when it acquired Sun Microsystems.

Java has remained the most popular language in the world for several years now (as at July 2018), according to the TIOBE index.

Java is both and . Instead of translating programs directly into machine language, the Java compiler generates byte code. Byte code is portable, so it is possible to compile a Java program on one machine, transfer the byte code to another machine, and run the byte code on the other machine. That’s why Java is considered a platform independent technology, aka WORA (Write Once Run Anywhere). The interpreter that runs byte code is called a “Java Virtual Machine” (JVM).

Java technology is both a programming language and a platform. The Java programming language is a high-level object-oriented language that has a particular syntax and style. A Java platform is a particular environment in which Java programming language applications run. --Oracle

According to the Official Java documentation, there are four platforms of the Java programming language:

• Java Platform, Standard Edition (Java SE): Contains the core functionality of the Java programming language.

• Java Platform, Enterprise Edition (Java EE): For developing and running large-scale enterprise applications. Built on top of Java SE.

• Java Platform, Micro Edition (Java ME): For Java programming language applications meant for small devices, like mobile phones. A subset of Java SE.

• JavaFX: For creating applications with graphical user interfaces. Can work with the other three above.

This book chapter uses the Java SE edition unless stated otherwise.

To run Java programs, you only need to have a recent version of the Java Runtime Environment (JRE) installed in your device.

If you want to develop applications for Java, download and install a recent version of the Java Development Kit (JDK), which includes the JRE as well as additional resources needed to develop Java applications.

In Java, the HelloWorld program looks like this:

public class HelloWorld {

    public static void main(String[] args) {
        // generate some simple output
        System.out.println("Hello, World!");
    }
}

    

    


    
    
    

      


    
    

For reference, the equivalent C++ code is given below:

#include <iostream>
using namespace std;

int main() {
    // generate some simple output
    cout << "Hello, World!";
    return 0;
}

    

    


    
    
    

      


    
    

This HelloWorld Java program defines one method named main: public static void main(String[] args)

System.out.println() displays a given text on the screen.

Some similarities:

• Java programs consists of statements, grouped , which are then grouped into classes.
• Java is “case-sensitive”, which means SYSTEM is different from System.
• public is an access modifier that indicates the method is accessible from outside this class. Similarly, private access modifier indicates that a method/attribute is not accessible outside the class.
• static indicates this method is defined as a class-level member. Do not worry if you don’t know what that means. It will be explained later.
• void indicates that the method does not return anything.
• The name and format of the main method is special as it is the method that Java executes when you run a Java program.
• A class is a collection of methods. This program defines a class named HelloWorld.
• Java uses squiggly braces ({ and }) to group things together.
• The line starting with // is a comment. You can use // for single line comments and /* ... */ for multi-line comments in Java code.

Some differences:

• Java use the term method instead of function. In particular, Java doesn’t have stand-alone functions. Every method should belong to a class. The main method will not work unless it is inside the HelloWorld class.
• A Java class definition does not end with a semicolon, but most Java statements do.
• In most cases (i.e., there are exceptions), the name of the class has to match the name of the file it is in, so this class has to be in a file named HelloWorld.java.
• There is no need for the HelloWorld code to have something like #include <iostream>. The library files needed by the HelloWorld code is available by default without having to "include" them explicitly.
• There is no need to return 0 at the end of the main method to indicate the execution was successful. It is considered as a successful execution unless an error is signalled specifically.

To compile the HelloWorld program, open a command console, navigate to the folder containing the file, and run the following command.

>_ javac HelloWorld.java

If the compilation is successful, you should see a file HelloWorld.class. That file contains the byte code for your program. If the compilation is unsuccessful, you will be notified of the compile-time errors.

Notes:

• javac is the java compiler that you get when you install the JDK.
• For the above command to work, your console program should be able to find the javac executable (e.g., In Windows, the location of the javac.exe should be in the PATH system variable).
  This page shows how to set PATH in different OS'es.

To run the HelloWorld program, in a command console, run the following command from the folder containing HelloWorld.class file.

>_ java HelloWorld

Notes:

• java in the command above refers to the Java interpreter installed in your computer.
• Similar to javac, your console should be able to find the java executable.

When you run a Java program, you can encounter a . These errors are also called "exceptions" because they usually indicate that something exceptional (and bad) has happened. When a run-time error occurs, the interpreter displays an error message that explains what happened and where.

System.out.println(5/0);

    

    


    
    
    

      


    
    

Exception in thread "main" java.lang.ArithmeticException: / by zero
    at Hello.main(Hello.java:5)

    

    


    
    
    

      


    
    

Integrated Development Environments (IDEs) can automate the intermediate step of compiling. They usually have a Run button which compiles the code first and then runs it.

Example IDEs:

• IntelliJ IDEA
• Eclipse
• NetBeans

Java has a number of primitive data types, as given below:

• byte: an integer in the range -128 to 127 (inclusive).
• short: an integer in the range -32,768 to 32,767 (inclusive).
• int: an integer in the range -2³¹ to 2³¹-1.
• long: An integer in the range -2⁶³ to 2⁶³-1.
• float: a single-precision 32-bit IEEE 754 floating point. This data type should never be used for precise values, such as currency. For that, you will need to use the java.math.BigDecimal class instead.
• double: a double-precision 64-bit IEEE 754 floating point. For decimal values, this data type is generally the default choice. This data type should never be used for precise values, such as currency.
• boolean: has only two possible values: true and false.
• char: The char data type is a single 16-bit Unicode character. It has a minimum value of '\u0000' (or 0) and a maximum value of '\uffff' (or 65,535 inclusive).

The String type (a peek)

Java has a built-in type called String to represent strings. While String is not a primitive type, strings are used often. String values are demarcated by enclosing in a pair of double quotes (e.g., "Hello"). You can use the + operator to concatenate strings (e.g., "Hello " + "!").

You’ll learn more about strings in a later section.

Java is a statically-typed language in that variables have a fixed type. Here are some examples of declaring variables and assigning values to them.

int x;
x = 5;
int hour = 11;
boolean isCorrect = true;
char capitalC = 'C';
byte b = 100;
short s = 10000;
int i = 100000;

    

    


    
    
    

      


    
    

You can use any name starting with a letter, underscore, or $ as a variable name but you cannot use Java keywords as variables names. You can display the value of a variable using System.out.print or System.out.println (the latter goes to the next line after printing). To output multiple values on the same line, it’s common to use several print statements followed by println at the end.

int hour = 11;
int minute = 59;
System.out.print("The current time is ");
System.out.print(hour);
System.out.print(":");
System.out.print(minute);
System.out.println("."); //use println here to complete the line
System.out.println("done");

    

    


    
    
    

      


    
    

The current time is 11:59.
done

    

    


    
    
    

      


    
    

Use the keyword final to indicate that the variable value, once assigned, should not be allowed to change later i.e., act like a ‘constant’. By convention, names for constants are all uppercase, with the underscore character (_) between words.

final double CM_PER_INCH = 2.54;

    

    


    
    
    

      


    
    

Java supports the usual arithmetic operators, given below.

The following program uses some operators as part of an expression hour * 60 + minute:

int hour = 11;
int minute = 59;
System.out.print("Number of minutes since midnight: ");
System.out.println(hour * 60 + minute);

    

    


    
    
    

      


    
    

Number of minutes since midnight: 719

    

    


    
    
    

      


    
    

When an expression has multiple operators, normal operator precedence rules apply. Furthermore, you can use parentheses to specify a precise precedence.

Java does not allow .

The unary operators require only one operand; they perform various operations such as incrementing/decrementing a value by one, negating an expression, or inverting the value of a boolean.-- Java Tutorial

Relational operators are used to check conditions like whether two values are equal, or whether one is greater than the other. The following expressions show how they are used:

The result of a relational operator is a boolean value.

Java has three conditional operators that are used to operate on boolean values.

Arrays are indicated using square brackets ([]). To create the array itself, you have to use the new operator. Here are some example array declarations:

int[] counts;
counts = new int[4]; // create an int array of size 4

int size = 5;
double[] values;
values = new double[size]; //use a variable for the size

double[] prices = new double[size]; // declare and create at the same time

    

    


    
    
    

      


    
    

Alternatively, you can use the shortcut syntax to create and initialize an array:

int[] values = {1, 2, 3, 4, 5, 6};

int[] anArray = {
    100, 200, 300,
    400, 500, 600,
    700, 800, 900, 1000
};

    

    


    
    
    

      


    
    

-- Java Tutorial

The [] operator selects elements from an array. Array elements .

int[] counts = new int[4];

System.out.println("The first element is " + counts[0]);

counts[0] = 7; // set the element at index 0 to be 7
counts[1] = counts[0] * 2;
counts[2]++; // increment value at index 2

    

    


    
    
    

      


    
    

A Java array is aware of its size. A Java array prevents a programmer from indexing the array out of bounds. If the index is negative or not present in the array, the result is an error named ArrayIndexOutOfBoundsException.

int[] scores = new int[4];
System.out.println(scores.length) // prints 4
scores[5] = 0; // causes an exception

    

    


    
    
    

      


    
    

4
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 5
	at Main.main(Main.java:6)

    

    


    
    
    

      


    
    

It is also possible to create arrays of more than one dimension:

String[][] names = {
    {"Mr. ", "Mrs. ", "Ms. "},
    {"Smith", "Jones"}
};

System.out.println(names[0][0] + names[1][0]); // Mr. Smith
System.out.println(names[0][2] + names[1][1]); // Ms. Jones

    

    


    
    
    

      


    
    

-- Java Tutorial

Passing arguments to a program

The args parameter of the main method is an array of Strings containing command line arguments supplied (if any) when running the program.

public class Foo{
    public static void main(String[] args) {
        System.out.println(args[0]);
    }
}

    

    


    
    
    

      


    
    

You can run this program (after compiling it first) from the command line by typing:

>_ java Foo abc

abc

if-else statements

if (x > 0) {
    System.out.println("x is positive");
}

    

    


    
    
    

      


    
    

if (x % 2 == 0) {
    System.out.println("x is even");
} else {
    System.out.println("x is odd");
}

    

    


    
    
    

      


    
    

if (x > 0) {
    System.out.println("x is positive");
} else if (x < 0) {
    System.out.println("x is negative");
} else {
    System.out.println("x is zero");
}

    

    


    
    
    

      


    
    

if (x == 0) {
    System.out.println("x is zero");
} else {
    if (x > 0) {
        System.out.println("x is positive");
    } else {
        System.out.println("x is negative");
    }
}

    

    


    
    
    

      


    
    

if (x % 2 == 0)
    System.out.println("x is even");
else
    System.out.println("x is odd");

    

    


    
    
    

      


    
    

switch statements

public class SwitchDemo {
    public static void main(String[] args) {

        int month = 8;
        String monthString;
        switch (month) {
        case 1:  monthString = "January";
            break;
        case 2:  monthString = "February";
            break;
        case 3:  monthString = "March";
            break;
        case 4:  monthString = "April";
            break;
        case 5:  monthString = "May";
            break;
        case 6:  monthString = "June";
            break;
        case 7:  monthString = "July";
            break;
        case 8:  monthString = "August";
            break;
        case 9:  monthString = "September";
            break;
        case 10: monthString = "October";
            break;
        case 11: monthString = "November";
            break;
        case 12: monthString = "December";
            break;
        default: monthString = "Invalid month";
            break;
        }
        System.out.println(monthString);
    }
}

    

    


    
    
    

      


    
    

Defining methods

public class PrintTwice {

    public static void printTwice(String s) {
        System.out.println(s);
        System.out.println(s);
    }

    public static void main(String[] args) {
        String sentence = “Polly likes crackers”
        printTwice(sentence);

    }
}


    

    


    
    
    

      


    
    

Polly likes crackers
Polly likes crackers

    

    


    
    
    

      


    
    

return statements

public static void printLogarithm(double x) {
    if (x <= 0.0) {
        System.out.println("Error: x must be positive.");
        return;
    }
    double result = Math.log(x);
    System.out.println("The log of x is " + result);
}

    

    


    
    
    

      


    
    

public class AreaCalculator{

    public static double calculateArea(double radius) {
        double result = 3.14 * radius * radius;
        return result;
    }

    public static void main(String[] args) {
        double area = calculateArea(12.5);
        System.out.println(area);
    }
}

    

    


    
    
    

      


    
    

Overloading

public static double calculateArea(double radius) {
    //...
}

public static double calculateArea(double height, double width) {
    //...
}

    

    


    
    
    

      


    
    

Recursion

public static void nLines(int n) {
    if (n > 0) {
        System.out.println();
        nLines(n - 1);
    }
}

    

    


    
    
    

      


    
    

Java has while and for constructs for looping.

while loops

public static void countdown(int n) {
    while (n > 0) {
        System.out.println(n);
        n = n - 1;
    }
    System.out.println("Blastoff!");
}

    

    


    
    
    

      


    
    

for loops

for (initializer; condition; update) {
    statement(s);
}

    

    


    
    
    

      


    
    

public static void printTable(int rows) {
    for (int i = 1; i <= rows; i = i + 1) {
        printRow(i, rows);
    }
}

    

    


    
    
    

      


    
    

do-while loops

class DoWhileDemo {
    public static void main(String[] args){
        int count = 1;
        do {
            System.out.println("Count is: " + count);
            count++;
        } while (count < 11);
    }
}

    

    


    
    
    

      


    
    

break and continue

class Main {
    public static void main(String[] args) {
        int[] numbers = new int[] { 1, 2, 3, 0, 4, 5, 0 };
        for (int i = 0; i < numbers.length; i++) {
            if (numbers[i] == 0) {
                break;
            }
            System.out.print(numbers[i]);
        }
    }
}

    

    


    
    
    

      


    
    

123

    

    


    
    
    

      


    
    

public static void main(String[] args) {
    int[] numbers = new int[] { 1, 2, 3, 0, 4, 5, 0 };
    for (int i = 0; i < numbers.length; i++) {
        if (numbers[i] == 0) {
            continue;
        }
        System.out.print(numbers[i]);
    }
}

    

    


    
    
    

      


    
    

12345

    

    


    
    
    

      


    
    

Enhanced for loops

for (int i = 0; i < values.length; i++) {
    int value = values[i];
    System.out.println(value);
}

    

    


    
    
    

      


    
    

for (int value : values) {
    System.out.println(value);
}

    

    


    
    
    

      


    
    

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

Git is the most widely used RCS today. Other RCS tools include Mercurial, Subversion (SVN), Perforce, CVS (Concurrent Versions System), Bazaar, TFS (Team Foundation Server), and Clearcase.

Github is a web-based project hosting platform for projects using Git for revision control. Other similar services include GitLab, BitBucket, and SourceForge.

Let's take your first few steps in your Git journey.

1. First, install Sourcetree (installation instructions), 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.

2. Next, create a directory for the repo (e.g., a directory named things).

3. Then, initialize a repository in that directory.

Sourcetree

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.

Windows: you might have to configure Windows Explorer to show hidden files.

---

CLI

Open a Git Bash Terminal.

If you installed Sourcetree, you can click the Terminal button to open a GitBash terminal (on a Linux/Mac environment, even a regular terminal should do).

Navigate to the things directory.
Use the command git init which should initialize the repo.

$ cd /c/repos/things
$ git init

    

    


    
    
    

      


    
    

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

    

    


    
    
    

      


    
    

You can use the list all 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 following:

$ git status

    

    


    
    
    

      


    
    

# On branch master
#
# No commits yet
#
nothing to commit (create/copy files and use "git add" to track)

    

    


    
    
    

      


    
    

---

Tracking and ignoring

In a repo, you 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

After initializing a repository, Git can help you with revision controlling files inside the working directory. However, it is not automatic. You need to tell Git which of your changes (aka revisions) should be committed to its memory for later use. Saving changes into Git's memory in that way is called committing and a change saved to the revision history is called a commit.

Here are the steps you can follow to learn how to create Git commits:

1. Do some changes to the content inside the working directory e.g., create a file named fruits.txt in the things directory and add some dummy text to it.

2. Observe how the file is detected by Git.

Sourcetree

The file is shown as ‘unstaged’.

---

CLI

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

$ git status

    

    


    
    
    

      


    
    

# On branch master
#
# No commits yet
#
# 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)

    

    


    
    
    

      


    
    

---

3. Stage the changes to commit: Although Git has detected the file in the working directory, it will not do anything with the file unless you tell it to. Suppose you want to commit the current changes to the file. First, you should stage the file, which is how you tell Git which changes you want to include in the next commit.

Sourcetree

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

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

If Sourcetree shows a \ No newline at the end of the file message below the staged lines (i.e., below the cherries line in the above screenshot), that is because you did not hit enter after entering the last line of the file (hence, Git is not sure if that line is complete). To rectify, move the cursor to end of the last line in that file and hit enter (like you are adding a blank line below it). This new change will now appear as an 'unstaged' change. Stage it as well.

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CLI

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
#
# No commits yet
#
# Changes to be committed:
#   (use "git rm --cached <file>..." to unstage)
#
#       new file:   fruits.txt
#

    

    


    
    
    

      


    
    

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4. Commit the staged version of fruits.txt.

Sourcetree

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

---

CLI

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

    

    


    
    
    

      


    
    

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Note the existence of something called the master branch. Git uses a mechanism called branches to facilitate evolving file content in parallel (we'll learn git branching in a later topic). Furthermore, Git auto-creates a branch named master on which the commits go on by default.

Sourcetree

Expand the BRANCHES menu and click on the master to view the history graph, which contains only one node at the moment, representing the commit you just added. Also note a label master attached to the commit.

This label points to the latest commit on the master branch.

---

CLI

Run the git status command and note how the output contains the phrase on branch master.

---

5. Do a few more commits.

1. Make 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.

   

2. 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.

   
   You can decide what to stage and what to leave unstaged. When staging changes to commit, you can leave some files unstaged, if you wish to not include them in the next commit. In fact, Git even allows some changes in a file to be staged, while other changes in the same file to be unstaged. This flexibility is particularly useful when you want to put all related changes into a commit while leaving out unrelated changes.

6. See the revision graph: Note how commits form a path-like structure aka the revision tree/graph. In the revision graph, each commit is shown as linked to its 'parent' commit (i.e., the commit before it).

Sourcetree

To see the revision graph, click on the History item (listed under the WORKSPACE section) on the menu on the right edge of Sourcetree.

---

CLI

The gitk command opens a rudimentary graphical view of the revision graph.

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How do undo/delete a commit?

Sourcetree

To undo the last commit, right-click on the commit just before it, and choose Reset current branch to this commit.

In the next dialog, choose the mode Mixed - keep working copy but reset index option. This will make the offending commit disappear but will keep the changes that you included in that commit intact.

If you use the Soft - ... mode instead, the last commit will be undone as before, but the changes included in that commit will stay in the staging area.

To delete the last commit entirely (i.e., undo the commit and also discard the changes included in that commit), do as above but choose the Hard - ... mode instead.

To undo/delete last n commits, right-click on the commit just before the last n commits, and do as above.

---

CLI

To undo the last commit, but keep the changes in the staging area, use the following command.

$ git reset --soft HEAD~1

    

    


    
    
    

      


    
    

To undo the last commit, and remove the changes from the staging area (but not discard the changes), used --mixed instead of --soft.

$ git reset --mixed HEAD~1

    

    


    
    
    

      


    
    

To delete the last commit entirely (i.e., undo the commit and also discard the changes included in that commit), do as above but use the --hard flag instead (i.e., do a hard reset).

$ git reset --hard HEAD~1

    

    


    
    
    

      


    
    

To undo/delete last n commits: HEAD~1 is used to tell Git you are targeting the commit one position before the latest commit -- in this case the target commit is the one we want to reset to, not the one we want to undo (as the command used is reset). To undo/delete two last commits, you can use HEAD~2, and so on.

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Often, there are files inside the Git working folder that you don't want to revision-control e.g., temporary log files. Follow the steps below to learn how to configure Git to ignore such files.

1. Add a file into your repo's working folder that you supposedly don't want to revision-control e.g., a file named temp.txt. Observe how Git has detected the new file.

2. Configure Git to ignore that file:

temp.txt

    

    


    
    
    

      


    
    

temp.txt

    

    


    
    
    

      


    
    

Files recommended to be omitted from version control

• Binary files generated when building your project e.g., *.class, *.jar, *.exe (reasons: 1. no need to version control these files as they can be generated again from the source code 2. Revision control systems are optimized for tracking text-based files, not binary files.
• Temporary files e.g., log files generated while testing the product
• Local files i.e., files specific to your own computer e.g., local settings of your IDE
• Sensitive content i.e., files containing sensitive/personal information e.g., credential files, personal identification data (especially, if there is a possibility of those files getting leaked via the revision control system).

Remote repositories are repos that are hosted on remote computers and allow remote access. 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 codebase.

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

When you clone from a repo, the original repo is commonly referred to as the upstream repo. A repo can have multiple upstream repos. For example, let's say a repo repo1 was cloned as repo2 which was then cloned as repo3. In this case, repo1 and repo2 are upstream repos of repo3.

Cloning, pushing, and pulling can be done between two local repos too, although it is more common for them to involve a remote repo.

Given below is an example scenario you can try yourself to learn Git cloning.

Suppose you want to clone the sample repo samplerepo-things to your computer.

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

Some useful navigation shortcuts:

1. Quickly locate a file by name.
2. Go to the definition of a method from where it is used.
3. Go back to the previous location.
4. View the documentation of a method from where the method is being used, without navigating to the method itself.
5. Find where a method/field is being used.

Always code as if the person who ends up maintaining your code will be a violent psychopath who knows where you live. _{-- Martin Golding}

Production code needs to be of high quality. Given how the world is becoming increasingly dependent on software, poor quality code is something no one can afford to tolerate.

One essential way to improve code quality is to follow a consistent style. That is why software engineers usually follow a strict coding standard (aka style guide).

The aim of a coding standard is to make the entire codebase look like it was written by one person. A coding standard is usually specific to a programming language and specifies guidelines such as the locations of opening and closing braces, indentation styles and naming styles (e.g. whether to use Hungarian style, Pascal casing, Camel casing, etc.). It is important that the whole team/company uses the same coding standard and that the standard is generally not inconsistent with typical industry practices. If a company's coding standard is very different from what is typically used in the industry, new recruits will take longer to get used to the company's coding style.