Sulaimani Polytechnic University
TechnicalCollegeof Informatics
ComputerNetworksDepartment
By : Msc. Fariaa Abdulmajed

Introduction:-
Programming and programminglanguage
Programming: is the technique of converting the idea of solving a specified
problem into a logical related sequence of statements using a programming
language to obtain a required goal.
Programming language is a set of rules and symbols used to construct a
computer program

Programming Languages
Programming languages can be classified according to two criteria:
▪ Purpose of the Languages: This means, the objective that this language is
produced to.
▪ Level of the Language: This mean, the association level of the language from the
machine (microprocessor) or from the user (Human).

LanguagePurpose

Language Level

Compiler and Interpreter
• A program written in a high-level language is called a source
program or source code.
• A computer cannot execute a source program, a source program
must be translated into machine code for execution.
• The translation can be done using another programming tool
called an interpreter or a compiler.

Structureof Java programs
public class <name> {
public static void main(String[] args) {
<statement(s)>;
}
}
• Every executable Java program consists of a class...
• that contains a method named main...
• that contains the statements to be executed

Simple First Program: "Hello World"
public class Hello {
public static void main(String[] args) {
// Program execution begins here
System.out.println("Hello world.");
}
}

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public // Accessible outside this file. "public" is a reserved word.
class // "class" is a reservedword.
Hello// The name of the class - same name as filename.
{ // Braces instead of begin/end.
public // This function must be accessible. "public" is reserved.
static // "static"is reserved.
void // The return value - nothing. "void" is reserved.
main // To start execution, a class must have a "main" function.
(String[] args)
System.out.println ("Hello World!"); // useful function called println, which takes in a string and
prints it out on a new line.
SimpleFirstProgram:"HelloWorld"

Important Notes
▪Filenames must end with .java in lowercase letters.
▪Filenames must match their class names (more info on this
soon).
▪Filenames cannot contain spaces.
▪Filenames are case sensitive: firstTry.java vs.
FirstTry.java vs. FIRSTTRY.java
▪Filenames consist only of letters (A-Z, a-z), digits (0-9),
underscores (_), dashes (-) and periods (.).

System.out.println
• Java programs use a statement called System.out.println
to instruct the computer to print a line of output on the console
• Two ways to use System.out.println :
1. System.out.println("<Message>");
• System.out.println (“I love JAVA");.
2. System.out.println(mathematical computations);
• System.out.println ((3*4)+7-8);

AnotherJavaprogram
The code in this program instructs the computer to print four messages on
the screen.
public class Hello2 {
public static void main(String[] args) {
System.out.println("Hello, world!");
System.out.println();
System.out.println("This program produces");
System.out.println("four lines of output");
}
}

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Program Development Process
Text editor Source code
(.java)
Saves Java statements
Java compiler
Byte code
(.class)
Produces
Java
Virtual
Machine
Program
Execution
Results in

• All Java source files must end with the .java extension
• Those source files are then compiled into .class files by the javac compiler.
• it instead contains bytecodes — the machine language of the Java Virtual Machine (Java VM).
• The java launcher tool then runs your application with an instance of the Java Virtual Machine.
An overview of the software development process

• the Java VM is available on many different operating systems, the same .class files are capable of
running on Microsoft Windows,Linux, or Mac OS.
Through the Java VM, the same application is capable of running on multiple platforms

syntaxerrors & Runtime errors
• syntax error or compiler error: A problem in the structureof a program that causes the compiler to
fail.
• If you type yourJava program incorrectly, you may violate Java's syntax and see a syntax error.
public class Hello {
pooblic static void main(String[] args) {
System.owt.println("Hello, world!")_
}
}
H:summerHello.java:2: <identifier> expected
pooblic static void main(String[] args) {
^
H:summerHello.java:5: ';' expected
}
^
2 errors
Tool completed with exit code 1
compiler output:

Runtime errors are errors that cause a program to
terminate unusually.
WHEN we get Runtime errors!!!
1- if the program is running on the environment detects an
operation that is impossible to carry out.
2- If Input mistakes typically cause runtime errors
Ex : you have to read in a number, but you input string, this
causes data-type errors to occur in the program.
3- division by zero
System.out.println (12/0);

Comments
•Comments in Java can be one of two styles:
–Single line
•starts at //anywhere on a line
•ends at the end of that line
–Multi-line
•starts with character sequence /*anywhere
•ends with character sequence */anywhere after that
•can span multiple lines

Escapesequences
• Escape sequences,or escape characters, begin with a slash and are immediately followed by another
character.
• This two-character sequence,inside ""allows you to control your output (n, t, b)

lab work

1- write a program to execute “Hello, World! ” using TextPad
Step 1: Launch TextPad editor as demonstrated as follows:

Step 2: Write any sample Java program in the editor tool as
demonstrated as follows:
public class Hello {
public static void main(String [] arg) {
// Program execution begins here
System.out.println("Hello world.");
}
}

Step 3: Select ‘TextPad tools compile java’ choice from the Tools Menu
– > External Tools Sub Menu (or you can likewise use Ctrl+1 alternate
way key

Step 4: Ensure that the ‘Sava As’ dialog is shown. In ‘Save As’ dialog,
guarantee that ‘Save as Type’ is chosen as All Files, type ‘Hello.java’ into
the ‘File Name’ field and tap on ‘Save’ button as demonstrated as
follows:
Hello
Hello

Step 5: Repeat Step 3 to compile the saved Java document
Step 6: Select ‘Run Java Application’ alternative from the Tools Menu –
> External Tools Sub Menu (or you can likewise use Ctrl+2 easy shortcut
key)
Step 7: Observe that the outcome of the above composed Java
program is shown in the command window

2- what is the output of the following program and why
public class Ex1
{
public static void main ( String[] args )
{
System.out.println("HellontWorldn!" );
}
}

3) Write a java program to print your name . For example you get this output
4) Write a java program to output the following message.

5- what is the output of the following program
public class Ex1
{
public static void main ( String[] args )
{
System.out.println(12/4*(6+12)-8);
}
}

THANK YOU