Audience

Prerequisites

Execute Java Online

public class MyFirstJavaProgram {

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

• Object Oriented − In Java, everything is an Object. Java can be easily extended since it is based on the Object model.
• Platform Independent − Unlike many other programming languages including C and C++, when Java is compiled, it is not compiled into platform specific machine, rather into platform independent byte code. This byte code is distributed over the web and interpreted by the Virtual Machine (JVM) on whichever platform it is being run on.
• Simple − Java is designed to be easy to learn. If you understand the basic concept of OOP Java, it would be easy to master.
• Secure − With Java's secure feature it enables to develop virus-free, tamper-free systems. Authentication techniques are based on public-key encryption.
• Architecture-neutral − Java compiler generates an architecture-neutral object file format, which makes the compiled code executable on many processors, with the presence of Java runtime system.
• Portable − Being architecture-neutral and having no implementation dependent aspects of the specification makes Java portable. Compiler in Java is written in ANSI C with a clean portability boundary, which is a POSIX subset.
• Robust − Java makes an effort to eliminate error prone situations by emphasizing mainly on compile time error checking and runtime checking.
• Multithreaded − With Java's multithreaded feature it is possible to write programs that can perform many tasks simultaneously. This design feature allows the developers to construct interactive applications that can run smoothly.
• Interpreted − Java byte code is translated on the fly to native machine instructions and is not stored anywhere. The development process is more rapid and analytical since the linking is an incremental and light-weight process.
• High Performance − With the use of Just-In-Time compilers, Java enables high performance.
• Distributed − Java is designed for the distributed environment of the internet.
• Dynamic − Java is considered to be more dynamic than C or C++ since it is designed to adapt to an evolving environment. Java programs can carry extensive amount of run-time information that can be used to verify and resolve accesses to objects on run-time.

History of Java

Tools You Will Need

• Linux 7.1 or Windows xp/7/8 operating system
• Java JDK 8
• Microsoft Notepad or any other text editor

Try It Option

public class MyFirstJavaProgram {

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

What is Next?

Try it Option Online

We have set up the Java Programming environment online, so that you can compile and execute all the available examples online. It gives you confidence in what you are reading and enables you to verify the programs with different options. Feel free to modify any example and execute it online.

Try the following example using our online compiler available at CodingGround

public class MyFirstJavaProgram {

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

For most of the examples given in this tutorial, you will find a Try it option in our website code sections at the top right corner that will take you to the online compiler. So just make use of it and enjoy your learning.

Local Environment Setup

Setting Up the Path for Windows

• Right-click on 'My Computer' and select 'Properties'.
• Click 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 Linux, UNIX, Solaris, FreeBSD

Popular Java Editors

• Notepad − On Windows machine, you can use any simple text editor like Notepad (Recommended for this tutorial), TextPad.
• Netbeans − A Java IDE that is open-source and free which can be downloaded from https://www.netbeans.org/index.html.
• Eclipse − A Java IDE developed by the eclipse open-source community and can be downloaded from https://www.eclipse.org/.

What is Next?

• Object − Objects have states and behaviors. Example: A dog has states - color, name, breed as well as behavior such as wagging their tail, barking, eating. An object is an instance of a class.
• Class − A class can be defined as a template/blueprint that describes the behavior/state that the object of its type supports.
• Methods − A method is basically a behavior. A class can contain many methods. It is in methods where the logics are written, data is manipulated and all the actions are executed.
• Instance Variables − Each object has its unique set of instance variables. An object's state is created by the values assigned to these instance variables.

First Java Program

Example

public class MyFirstJavaProgram {

   /* This is my first java program.
    * This will print 'Hello World' as the output
    */

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

• Open notepad and add the code as above.
• Save the file as: MyFirstJavaProgram.java.
• Open a command prompt window and go to the directory where you saved the class. Assume it's C:\.
• Type 'javac MyFirstJavaProgram.java' and press enter to compile your code. If there are no errors in your code, the command prompt will take you to the next line (Assumption : The path variable is set).
• Now, type ' java MyFirstJavaProgram ' to run your program.
• You will be able to see ' Hello World ' printed on the window.

Output

C:\> javac MyFirstJavaProgram.java
C:\> java MyFirstJavaProgram 
Hello World

Basic Syntax

• Case Sensitivity − Java is case sensitive, which means identifier Hello and hello would have different meaning in Java.
• Class Names − For all class names the first letter should be in Upper Case. If several words are used to form a name of the class, each inner word's first letter should be in Upper Case.
  Example: class MyFirstJavaClass
• Method Names − All method names should start with a Lower Case letter. If several words are used to form the name of the method, then each inner word's first letter should be in Upper Case.
  Example: public void myMethodName()
• Program File Name − Name of the program file should exactly match the class name.
  When saving the file, you should save it using the class name (Remember Java is case sensitive) and append '.java' to the end of the name (if the file name and the class name do not match, your program will not compile).
  Example: Assume 'MyFirstJavaProgram' is the class name. Then the file should be saved as 'MyFirstJavaProgram.java'
• public static void main(String args[]) − Java program processing starts from the main() method which is a mandatory part of every Java program.

Java Identifiers

• All identifiers should begin with a letter (A to Z or a to z), currency character ($) or an underscore (_).
• After the first character, identifiers can have any combination of characters.
• A key word cannot be used as an identifier.
• Most importantly, identifiers are case sensitive.
• Examples of legal identifiers: age, $salary, _value, __1_value.
• Examples of illegal identifiers: 123abc, -salary.

Java Modifiers

• Access Modifiers − default, public , protected, private
• Non-access Modifiers − final, abstract, strictfp

Java Variables

• Local Variables
• Class Variables (Static Variables)
• Instance Variables (Non-static Variables)

Java Arrays

Java Enums

Example

class FreshJuice {
   enum FreshJuiceSize{ SMALL, MEDIUM, LARGE }
   FreshJuiceSize size;
}

public class FreshJuiceTest {

   public static void main(String args[]) {
      FreshJuice juice = new FreshJuice();
      juice.size = FreshJuice.FreshJuiceSize.MEDIUM ;
      System.out.println("Size: " + juice.size);
   }
}

Output

Size: MEDIUM

Java Keywords

Comments in Java

Example

public class MyFirstJavaProgram {

   /* This is my first java program.
    * This will print 'Hello World' as the output
    * This is an example of multi-line comments.
    */

   public static void main(String []args) {
      // This is an example of single line comment
      /* This is also an example of single line comment. */
      System.out.println("Hello World");
   }
}

Output

Hello World

Using Blank Lines

Inheritance

Interfaces