Introduction to Java

Why java?

• Platform Independence: Write once, run anywhere (JVM-based).
• Object-Oriented: Encourages reusable and maintainable code.
• Rich API: Extensive libraries for development.
• Multithreading: Built-in support for concurrent programming.
• Security: Strong security features for safe execution.
• Scalability: Ideal for building large, scalable systems.
• Community Support: Large, active community and resources.
• Performance: Optimized with Just-In-Time (JIT) compilation.
• Enterprise Adoption: Widely used in large-scale enterprise applications.

Setting up java

• Download and install jdk. Jdk contains

• Install the jdk by following the installation instruction.

• Set Up Environment Variables

  • To use javac and java from any command prompt, we need to configure environment variables.
    • Open Environment Variables:
      • Right-click on This PC > Properties > Advanced system settings > Environment Variables.
    • Add JAVA_HOME(Not mandatory):
      • Under System Variables, click New.
      • Name: JAVA_HOME
      • Value: Path to your JDK installation (e.g., C:\Program Files\Java\jdk-XX).
    • Update Path Variable:
      • In System Variables, find and edit Path.
      • Add a new entry: %JAVA_HOME%\bin.
      • You can directly add the bin without the JAVA_HOME also.
    • Apply Changes:

      

      - Click ok and save the changes.

• Verify Installation

  • Open Command Prompt and run the following commands:
    • Check java (Java Compiler):

      java -version
      

    • Check javac (Java Compiler):

      javac -version
      

Program execution

• Let's write a simple java program first:

  public class FirstProgram {
  
      public static void main(String... args){
          System.out.println("Hello world");
      }
  }
  

  • Make sure to save it with .java extension with file name same as class name. FirstProgram.java.

• Compile Java

  • Now we need to compile the file.
  • For compiling via cmd, we can use

    javac FirstProgram.java
    

  • If there are no error, it will create a file named FirstProgram.class. See the .class extension.
  • This generated file contains bytecode which is machine independent.
  • Content of generated file:

    Êþº¾   = 
         
     java/lang/Object
     <init>
     ()V            
     
    
     java/lang/System
     out
     Ljava/io/PrintStream; 
     
    Hello world
         
     java/io/PrintStream
      println
     (Ljava/lang/String;)V  
     FirstProgram
     Code
     LineNumberTable
     main
     ([Ljava/lang/String;)V
     
    SourceFile
     FirstProgram.java !        
       
         
     
       *· 
    ±   
         
       
     ‰   
        %  
           ²  
    ¶ ±   
        
          
         
    

• Executing the code

  • For executing the .class file, we can use the following command

    java FirstProgram
    

    • See we are not using extension here.
  • Output of the code:

    Hello world