1. Java programming lecture one
Abdiasis abdallah

2. Chapter one: introduction
What is programming?
Programming means to create(develop) software, which is also called a program
Software contains the instructions that tell the computer what to do.

3. Intro Software is all around you personal computers
Word processors to write documents
Web browsers to explore the internet
programs to send and receive messages
Running airplanes, appliances, cell phones and so on
Software is created with the help of programming languages

4. This course teaches you how to program using Java
Before starting we review some basic concepts about computers
Computer hardware such as CPU, memory and storage
Operating systems

5. What is a computer An electronic device that stores and processes data
A computer contains both hardware and software
Hardware is the physical elements of the computer
Central processing unit (CPU)
Main memory
Storage devices (such as disks and devices)
Input devices (such as mouse and keyboard)
Output devices (such as monitor and printer)
Communication devices (such as network cards)

6. Programming languages
Machine language
Computer’s native language
A set of built-in primitive instructions in binary code
Assembly language
uses short descriptive word, know as mnemonic
Add 2,3,result means add 2 and 3 and get result
Assembler translates assemble language to machine
It is machine dependent
High-level language
Platform independent

7. Operating system Manages and controls computer’s activities
Application programs such as web browser cannot run without OS.
Users and applications access computer hardware via OS.

8. OS Major tasks of an operating system
Controlling and monitoring system activities
Allocating and assigning system resources
Scheduling applications
Controlling and monitoring system activities
Recognizing input from the keyboard
Sending output to the monitor
Keeping track of files and folders on storage devices
Controlling peripheral devices such as printers
Allocating and assigning system resources
Determine what computer resources a program needs (CPU time, memory space, etc)
Allocate and assign them to run the program
Scheduling operations
Multiprogramming allows multiple programs to run simultaneously by sharing the same CPU. For example editing text in word process at the same time web browser is downloading a file.
Multithreading allows a single program to execute multiple tasks at the same time. For example editing and saving in word processor.
Multiprocessing (parallel processing) uses two or more processors together to perform subtasks concurrently and then combine solutions

9. Java and WWW
Java is powerful programming language for developing software running on mobile devices, desktop computer and servers.
It was developed by sun micro-systems
Designed in 1991
WWW is an electronic repository that can be accessed on the internet from anywhere in the world.

10. Java language specifications
Java syntax is defined in the java language specification
Java library is defined in java API
JDK is the software for developing and running java programs
API (application program interface)
JDK (java development kit)

11. A simple java program
A java program is executed from main method in the class.

12. Program explanation Line 1 : defines class
Each java program must have at least one class
Each class has a name
By convention, class names start with uppercase letter
Java source codes are case sensitive. Replacing main with Main results in error

13. explanation Line 2 : defines the main method
The program is executed from main method
A method is a construct that contains statements
The main method in this program contains one statement (line 4) that displays the string “Welcome to java” on the console
Every statement in java end with a semicolon, known as a statement terminator.

14. Reserved words
Class, public, static, are examples of reserved words or keywords
Keywords have specific meaning to the compiler, and cannot be used for other purposes in the program.

15. Comments Line 3 : comment Program documentation
Ignored by the compiler
Preceded by // on single line comment
Enclosed between /* */ for block comment

16. Special characters

17. Creating, compiling and executing java programs
You save java program in .java file and compile it into .class file
The .class file is executed by java virtual environment
You can use any text editor or IDE to create and edit java source code
An example of IDE is eclipse
An example of editor is windows notepad
A java compiler translates java source file into java bytecode file

18. Java program development process
Java language is a high level language, but java bytecode is a low level language.
The bytecode is similar to machine instructions but architecture neutral and can run on any platform that has java virtual machine(JVM)
JVM is a program that interprets java bytecode

19. JVM

20. Tips
If you execute a class file that does not exist a NoClassDefFoundError will occur
If you execute a class file that does not have a main method or you mistyped the main, a NoSuchMethodError will occur
When executing a java program, the JVM first loads the bytecode of the class to memory using a program called the class loader.
After a class is loaded, the JVM uses a program called the bytecode verifier to check the validity of the bytecode.

21. Programming errors Syntax errors Runtime errors Logic errors
Also called compile errors
Detected by the compiler
Results from mistyped a keyword, omitting punctuation or not closing a brace
Runtime errors
Cause program to terminate abnormally
Input mistakes e.g division by zero
Logic errors

22. Common errors Missing closing brace Missing semicolon
Missing quotation marks for strings
Misspelling names