Overview of This Lesson

This lesson introduces you to programming and the Java language. it might be tempting to skip this lesson if you've already learned another language or have learned a bit of Java before, but I go over some details that many other books and courses skip over. These details will make it easier to understand how we write programs and this will in turn help you solve problems more easily.

In this lesson we'll cover the following:

• Overview of this Lesson
• What is Programming?
• How do we Write Programs?
• How do we Write Java Programs?

What is Programming?

What is programming? What does a programmer do, exactly?

You likely use many different applications (programs) on your computer: your browser is an application, any games you play are applications, even your operating system (e.g. Windows, Mac OS, Linus) are applications. On your phone, you have so many applications - pretty much any icon you see is an application, and there are several applications that aren't represented by those visual icons that work behind the scenes.

Where do these applications come from? Developers and designers work together to create and write these applications. Some programs are written by a team of developers; some programs are small and written by one developer.

You probably already have an idea that a programmer, or coder sits at the computer all day and their fingers magically fly over the keys at great speeds while symbols and characters rapidly appear on the screen. This is how many programmers are portrayed on TV and in movies. Some of this image of coding is true, but programming doesn't only involve sitting at a computer writing code. Programming often also includes other activities such as:

• Exploratory activities and critical thinking
  • analysing an existing system and data flows
  • interviewing and gathering information from users
  • doing research, taking extra classes/seminars, going to conferences
  • designing applications (user interfaces, UML diagrams, data flow, etc)
• Writing
  • internal program documentation (in your code)
  • external documentation (help files for users, API documentation for other programmers)
  • reports and emails to client or team leads
• Dealing with People
  • working with other programmers/analysts
  • presenting to a client or team
  • training users, helping users with problems

Some of the activites above may sound appealing and some may not be appealing to you at all; some might seem exciting and some might seem boring or frightening. So don't panic, these tutorials are all about coding. Perhaps you just want to code and deal only with the computer. That's fine. If you're in a college or university program, you'll likely take courses that focus on many of the activities mentioned above. But if you found these pages, you're probably most interested in programming or coding, even if it's just for the moment. That's fine, too.. but note that in order to become a good coder, you will have to become a good critical thinker and problem solver, so these tutorials will include activities and exercises that will help you with those things, too.

So, What is Coding, Then?

The coding part of programming involves using a programming language to give the computer instructions that perform various tasks. Today we use high-level languages to write code: languages like Java, Visual Basic, C++, and hundreds of others.

Don't worry, you don't need to learn all of those languages. Some people only know one or two, lots of people know several. At the time I last updated this page, I knew 11 programming languages (not counting markup languages like HTML), but about half of them aren't used much anymore. Some I have forgotten because I haven't used them in years. Today I mostly code with 2 or 3. If you learn one language really, really well, you'll find it really easy to learn a new language. Most programming languages use the same logical structures, they work in similar ways, and have a lot of the same features and characteristics. So once you learn one language, learning another one is quick and easy.

As you start working through these tutorials, make sure you've got Java installed, an Editor or IDE, and a note book and pen or pencil (or a device you can write on, like a tablet with a stylus). Yes, you will need to write things down, but also draw things like diagrams, tables, and flow charts. You won't ONLY be coding: you'll also be using your critical thinking skills and you'll be problem solving, and some of the activities are best done by writing and drawing!

How we Write Programs

Evolution of Programming Languages

When you write code, you're generally using a high-level language. Java is a high-level language, and so are languages like Python, C/C++, Ruby, and Turing. High-level languages are English-like and can be read by other programmers.

Prior to the invention of high-level languages, developers had to code in lower-level languages. For example, in the beginning, we only had machine language. Machine language is basically just binary code, or a series of 1's and 0's, or even hexadecimal code (digits from 0 to 9, along with the letters from A to F). A machine language is the native language of a particular platform. A platform consists of the combination of an operating system and hardware. For example, the PC platform is a combination of an IBM-type PC configuration with Microsoft Windows installed. The Mac platform is an Apple-type computer configuration with Mac OS installed. The machine language for a PC machine is different from the machine language for a Mac machine. If you wanted to write a program that worked for both Mac and PC, you would have to write it in two different machine languages.

Eventually, assembly languages were developed to help make programming easier. Assembly consisted of abbreviations for specific types of operations (such as ADD for addition or MOV to move data from one memory location to another). This was still very low-level programming: a command to add two numbers involved several statements to move and copy digits to and from memory registers (locations in memory). Assembly was not like machine language in that it was similar between different platforms, however a machine did not "speak" assembly so it couldn't run assembly programs. Instead, the developer would have to take their finished assembly code and assemble the code into machine code using an Assembler program. This machine code could then be read and executed by the platform on which the code was compiled. For example, if you compiled the code on a PC, it would only run on a PC, and if you compiled the code on a Mac, it would only run on a Mac. Even though you still had to compile a program for different platforms, it was still much easier than writing the program more than once in different machine languages.

.model small
.data
opr1 dw 1234h
opr2 dw 0002h
result dw 01 dup(?),\'$\'
.code
    mov ax,@data
    mov ds,ax
    mov ax,opr1
    mov bx,opr2
    clc
    add ax,bx
    mov di,offset result
    mov [di], ax

    mov ah,09h
    mov dx,offset result
    int 21h

    mov ah,4ch
    int 21h
    end

You can clearly understand now how high-level languages are much easier to read and learn! However, high-level language code is also not understood by a machine - remember, a machine only understands machine code. Therefore, there needs to be a way to convert your high-level source code that you write into machine language. This is the job of the compiler.

How Programs are Written

To write programs in any language you use an editor or an IDE (Integrated Development Environment). Editors are generally very simple, and good for first-time programmers. IDEs are more complex and include debugging tools, project management, memory management, design features, testing tools, and often many other things. In a lot of the introductory lessons of this course I'll be using Notepad++ or IntelliJ but in later tutorials I'll be using various IDEs. The Installation Instructions includes instructions for IntelliJ and VS Code.

Source Code is the actual code that you type into an editor or IDE. Source code is generally just plain text, so you could actually use any editor or even a word processor to write it, although most developers prefer an editor or IDE that's geared towards Java programming because of the extra features that those tools have. Even the most basic editor will include syntax highlighting, which will assign different colours and formatting to different words and symbols in your source code to show how they fit into the Java language.

Once you've written some source code, you compile that code. A compiler translates your high-level language source code into machine language that the computer can read and execute. Compiling your code will check your code for syntax errors, or errors in the spelling/grammar of the programming language. If you have any syntax errors, you'll need to fix them and then recompile your code.

Successful compilation of the source code results in a machine language file or program that can actually run on the computer. Usually this is an .exe or Executable file.

Machine language is specific to a particular machine, so if you compile your source code on a PC, that machine code can only run on a PC. If you compile that code on a Mac, you can only run that program on a Mac. Also, remember that there are hundreds of languages you could program with, so each language has to come with its own set of compilers for the various kinds of machines. As with Assembly, you will have to compile your code with the different compilers if you wanted to create executable files for each kind of machine (Windows, Mac, Linux, etc.)

A compiler does more than translates source code into machine language. It also checks your code's syntax. Syntax refers to the grammar and spelling of the programming language. For example, it ensures you have all the right punctuation and symbols and that you haven't spelled any words wrong. If you have any syntax errors in your code, the compiler will list them all for you, and it will not compile the source code into machine code. You then have to fix your syntax errors and try the compiler again. You repeat this process until the compiler finds no syntax errors, in which case it will translate your source code into machine language.

Larger and more complex programs also use a program called a linker that allows the developer to add other libraries to their program. A library is a collection of code that is already written and can be used in any other program. For example, if you want your program to use a credit card validation service that someone else wrote, you obtain that library and add it to your program. This is often done with programs that use operating system components, such as the standard set of file open/save dialog boxes. The linker takes the library (or libraries) and adds them to the machine code for your program and creates an executable file that can be run on the computer.