PHP 5 Tutorial

PHP is a server scripting language, and a powerful tool for making dynamic and interactive Web pages.

What is PHP?

• PHP is an acronym for "PHP: Hypertext Preprocessor"
• PHP is a widely-used, open source scripting language
• PHP scripts are executed on the server
• PHP is free to download and use

What is a PHP File?

• PHP files can contain text, HTML, CSS, JavaScript, and PHP code
• PHP code are executed on the server, and the result is returned to the browser as plain HTML
• PHP files have extension ".php"

Why PHP?

• PHP runs on various platforms (Windows, Linux, Unix, Mac OS X, etc.)
• PHP is compatible with almost all servers used today (Apache, IIS, etc.)
• PHP supports a wide range of databases
• PHP is free. Download it from the official PHP resource: www.php.net
• PHP is easy to learn and runs efficiently on the server side

Classes and Objects

Class

Class can be defined as a template/ blueprint that describe the behaviors /states of a particular entity

A class is declared using class keyword. A class contain both data and code that operate on that data. The data or variables defined within a class are called instance variables and the code that operates on this data is known as methods

Rules for java Class

• A class can have only public or default(no modifier) access specifier.
• It can be either abstract, final or concrete (normal class).
• A class can have extend only one one class/abstract class.
• It must have the class keyword, and class must be followed by a legal identifier(name).
• It may optionally extend one parent class. By default, it will extend java.lang.Object.
• It may optionally implement any number of comma-separated interfaces.
• The class's variables and methods are declared within a set of curly braces {}.
• Each .java source file may contain only one public class. A source file may contain any number of default visible classes.
• Finally, the source file name must match the public class name and it must have a .java suffix.

A simple class Example

Suppose, Student is a class and student's name, roll number, age will be its property. Lets see this in Java syntax

class Student.
{
 String name;
 int rollno;
 int age;
}

Object

Object is an instance of class. You may also call it as physical existence of a logical template class.

or

what you see in naked eye is called Object.

When a reference is made to a particular student with its property then it becomes an object, physical existence of Student class.

Student std=new Student();

After the above statement std is instance/object of Student class. Here the new keyword creates an actual physical copy of the object and assign it to the std variable. It will have physical existence and get memory in heap area. The new operator dynamically allocates memory for an object

Data Types in Java

Data Types in Java

Java language has a rich implementation of data types. Data types specify size and the type of values that can be stored in an identifier.

In java, data types are classified into two catagories :

1.     Primitive Data type

2.     Non-Primitive Data type

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1) Primitive Data type

A primitive data type can be of eight types :

1)Byte

2)Short

3)Int

4)Long

5)Float

6)Double

7)Char

8)Boolean

Once a primitive data type has been declared its type can never change, although in most cases its value can change. These eight primitive type can be put into four groups

Integer

This group includes byte, short, int, long

byte : It is 8 bit integer data type. Value range from -128 to 127. Default value zero. example: byte b=10;

short : It is 16 bit integer data type. Value range from -32768 to 32767. Default value zero. example:short s=11;

int : It is 32 bit integer data type. Value range from -2147483648 to 2147483647. Default value zero. example:int i=10;

long : It is 64 bit integer data type. Value range from -9,223,372,036,854,775,808 to 9,223,372,036,854,775,807. Default value zero. example: long l=100012;

Floating-Point Number

This group includes float, double

float : It is 32 bit float data type. Default value 0.0f. example: float ff=10.3f;

double : It is 64 bit float data type. Default value 0.0d. example: double db=11.123;

Characters

This group represent char, which represent symbols in a character set, like letters and numbers.

char : It is 16 bit unsigned unicode character. Range 0 to 65,535. example: char c='a';

Boolean

This group represent boolean, which is a special type for representing true/false values. They are defined constant of the language. example: boolean b=true;

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2) Non-Primitive(Reference) Data type

A reference data type is used to refer to an object. A reference variable is declare to be of specific and that type can never be change. We will talk a lot more about reference data type later in Classes and Object lesson.

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Identifiers in Java

All Java components require names. Name used for classes, methods, interfaces and variables are calledIdentifier. Identifier must follow some rules. Here are the rules:

·         All identifiers must start with either a letter( a to z or A to Z ) or currency character($) or an underscore.

·         After the first character, an identifier can have any combination of characters.

·         A Java keyword cannot be used as an identifier.

·         Identifiers in Java are case sensitive, foo and Foo are two different identifiers.

First Java Program

First Java Program

Let us look at a simple java program.

class Hello
{
  public static void main(String[] args) 
  {
     System.out.println ("Hello World program");
  }
}

class : class kyword is used to declare classes in Java

public : It is an access specifier. Public means this function is visible to all.

static : static is again a keyword used to make a function static. To execute a static function you do not have to create an Object of the class. The main() method here is called by JVM, without creating any object for class.

void : It is the return type, meaning this function will not return anything.

main : main() method is the most important method in a Java program. This is the method which is executed, hence all the logic must be inside the main() method. If a java class is not having a main() method, it causes compilation error.

System.out.println : This is used to print anything on the console like printf in C language.

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Steps to Compile and Run your first Java program

Step 1: Open a text editor and write the code as above.

Step 2: Save the file as Hello.java

Step 3: Open command prompt and go to the directory where you saved your first java program assuming it is saved in C:\

Step 4: Type javac Hello.java and press Return to compile your code. This command will call the Java Compiler asking it to compile the specified file. If there are no errors in the code the command prompt will take you to the next line.

Step 5: Now type java Hello on command prompt to run your program.

Step 6: You will be able to see Hello world program printed on your command prompt.

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Now let us see What happens at Runtime

After writing your Java program, when you will try to compile it. Compiler will perform some compilation operation on your program.

Once it is compiled successfully byte code(.class file) is generated by the compiler.

After compiling when you will try to run the byte code(.class file), the following steps are performed at runtime:-

1. Class loader loads the java class. It is subsystem of JVM Java Virtual machine.
2. Byte Code verifier checks the code fragments for illegal codes that can violate access right to the object.
3. Interpreter reads the byte code stream and then executes the instructions, step by step.

Features of Java

Features of Java

1) Simple

Java is easy to learn and its syntax is quite simple, clean and easy to understand.The confusing and ambiguous concepts of C++ are either left out in Java or they have been re-implemented in a cleaner way.

Eg : Pointers and Operator Overloading are not there in java but were an important part of C++.

2) Object Oriented

In java everything is Object which has some data and behaviour. Java can be easily extended as it is based on Object Model.

3) Robust

Java makes an effort to eliminate error prone codes by emphasizing mainly on compile time error checking and runtime checking. But the main areas which Java improved were Memory Management and mishandled Exceptions by introducing automatic Garbage Collector and Exception Handling.

4) Platform Independent

Unlike other programming languages such as C, C++ etc which are compiled into platform specific machines. Java is guaranteed to be write-once, run-anywhere language.

On compilation Java program is compiled into bytecode. This bytecode is platform independent and can be run on any machine, plus this bytecode format also provide security. Any machine with Java Runtime Environment can run Java Programs.

5) Secure

When it comes to security, Java is always the first choice. With java secure features it enable us to develop virus free, temper free system. Java program always runs in Java runtime environment with almost null interaction with system OS, hence it is more secure.

6) Multi Threading

Java multithreading feature makes it possible to write program that can do many tasks simultaneously. Benefit of multithreading is that it utilizes same memory and other resources to execute multiple threads at the same time, like While typing, grammatical errors are checked along.

7) Architectural Neutral

Compiler generates bytecodes, which have nothing to do with a particular computer architecture, hence a Java program is easy to intrepret on any machine.

8) Portable

Java Byte code can be carried to any platform. No implementation dependent features. Everything related to storage is predefined, example: size of primitive data types

9) High Performance

Java is an interpreted language, so it will never be as fast as a compiled language like C or C++. But, Java enables high performance with the use of just-in-time compiler.

Local Environment Setup

Local Environment Setup

Java SE is freely available from the link Download JAVA. So you download a version based on your operating system.

Follow the instructions to download java and run the .exe to install Java on your machine. Once you installed Java on your machine, you would need to set environment variables to point to correct installation directories:

Setting up the path for windows 2000/XP:

Assuming you have installed Java in c:\Program Files\java\jdk directory:

• Right-click on 'My Computer' and select 'Properties'.
• Click on the 'Environment variables' button under the 'Advanced' tab.
• Now, alter the 'Path' variable so that it also contains the path to the Java executable. Example, if the path is currently set to 'C:\WINDOWS\SYSTEM32', then change your path to read 'C:\WINDOWS\SYSTEM32;c:\Program Files\java\jdk\bin'.

Setting up the path for windows 7/8/8.1:

Assuming you have installed Java in c:\Program Files\java\jdk directory:

• Right-click on 'My Computer' and select 'Properties'.
  
• Click on the 'Advance System Settings' button.
  
• Now, alter the 'Path' variable so that it also contains the path to the Java executable. Example, if the path is currently set to 'C:\WINDOWS\SYSTEM32', then change your path to read 'C:\WINDOWS\SYSTEM32;c:\Program Files\java\jdk\bin'.
  

Popular Java Editors:

• To write your Java programs, you will need a text editor. There are even more sophisticated IDEs available in the market. But for now, you can consider one of the following:
  • Notepad: On Windows machine you can use any simple text editor like Notepad,NotePad++.
  • Netbeans:is a Java IDE that is open-source and free which can be downloaded from here.
  • Eclipse javaEE: is also a Java IDE developed by the eclipse open-source community and can be downloaded from here.

What is JAVA?

Java is a programming language and a platform.
Java is a high level, robust, secured and object-oriented programming language

Where it is Used?

1. Desktop Applications such as acrobat reader, media player, antivirus etc.
2. Web Applications.
3. Enterprise Applications such as banking applications.
4. Mobile
5. Embedded System
6. Smart Card
7. Robotics
8. Games etc.

Types of Java Applications

There are mainly 4 type of applications that can be created using java programming:

1) Standalone Application

It is also known as desktop application or window-based application. An application that we need to install on every machine such as media player, antivirus etc. AWT and Swing are used in java for creating standalone applications.

2) Web Application

An application that runs on the server side and creates dynamic page, is called web application. Currently, servlet, jsp, struts, jsf etc. technologies are used for creating web applications in java.

3) Enterprise Application

An application that is distributed in nature, such as banking applications etc. It has the advantage of high level security, load balancing and clustering. In java, EJB is used for creating enterprise applications.

4) Mobile Application

An application that is created for mobile devices. Currently Android and Java ME are used for creating mobile applications.