Java Editions Se Ee Me Complete Guide

Java SE (Standard Edition)

Java SE is the core platform for building Java applications. It includes core Java APIs and development tools. This example will focus on creating a simple "Hello, World!" application using Java SE.

Step-by-Step Example: Building a "Hello, World!" Application in Java SE

Step 1: Install Java Development Kit (JDK)

• Download JDK: Visit Oracle's JDK download page or use OpenJDK from AdoptOpenJDK.
• Install JDK: Follow the installation instructions specific to your operating system.

Step 2: Set Up Environment Variables

• Windows:

  1. Open System Properties -> Environment Variables.
  2. Add a new System Variable: JAVA_HOME with the path to your JDK installation (e.g., C:\Program Files\Java\jdk-17).
  3. Edit the Path variable and add %JAVA_HOME%\bin.

• macOS/Linux:

  export JAVA_HOME=/path/to/jdk
  export PATH=$JAVA_HOME/bin:$PATH
  

Step 3: Write the Java Code

Create a new file named HelloWorld.java and add the following code:

public class HelloWorld {
    public static void main(String[] args) {
        System.out.println("Hello, Java SE World!");
    }
}

Step 4: Compile the Java Code

Open a terminal or command prompt and navigate to the directory containing HelloWorld.java. Compile the code using:

javac HelloWorld.java

This command generates HelloWorld.class, which contains the bytecode.

Step 5: Run the Java Application

Execute the following command to run the program:

java HelloWorld

You should see the output:

Hello, Java SE World!

Java EE (Enterprise Edition)

Java EE is designed for building scalable, secure, and robust web applications. This example will demonstrate creating a simple "Hello, World!" web application using Java EE with Tomcat.

Prerequisites

• Java SE: Ensure a JDK is installed.
• Apache Tomcat: Download and install Apache Tomcat.

Step-by-Step Example: Building a Simple Web Application in Java EE

Step 1: Set Up Apache Tomcat

• Install Tomcat: Follow the installation instructions on the Apache Tomcat website.
• Start Tomcat: Navigate to the bin directory of your Tomcat installation and run:

  ./catalina.sh start  # For Linux/macOS
  catalina.bat start    # For Windows
  

Step 2: Write the Java Servlet

Create a new directory for your project, e.g., HelloJavaEE. Inside it, create a new directory structure for a web application:

HelloJavaEE/
└── src/
    └── com/
        └── example/
            └── HelloServlet.java

Add the following code to HelloServlet.java:

package com.example;

import java.io.IOException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@WebServlet("/greet")
public class HelloServlet extends HttpServlet {
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException {
        response.setContentType("text/html");
        response.getWriter().println("<h1>Hello, Java EE World!</h1>");
    }
}

Step 3: Create web.xml Deployment Descriptor

In the HelloJavaEE directory, create a WEB-INF/web.xml file to configure the servlet:

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee" 
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee 
         http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"
         version="3.1">
    <servlet>
        <servlet-name>HelloServlet</servlet-name>
        <servlet-class>com.example.HelloServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>HelloServlet</servlet-name>
        <url-pattern>/greet</url-pattern>
    </servlet-mapping>
</web-app>

Step 4: Package the Application

Use the jar command or prefer a build tool like Maven. Here, we'll use jar:

cd HelloJavaEE
jar -cvf HelloJavaEE.war .

Step 5: Deploy the Application to Tomcat

Copy the HelloJavaEE.war file to Tomcat's webapps directory:

cp HelloJavaEE.war /path/to/tomcat/webapps/

Step 6: Access the Application

Open a web browser and go to:

http://localhost:8080/HelloJavaEE/greet

You should see the message:

Hello, Java EE World!

Java ME (Micro Edition)

Java ME is targeted for resource-constrained devices, including mobile phones, smart cards, and set-top boxes. This example will demonstrate creating a simple "Hello, World!" application for Java ME.

Prerequisites

• Java ME SDK: Download and install the Java ME SDK.

Step-by-Step Example: Building a Simple "Hello, World!" Midlet for Java ME

Step 1: Set Up Java ME SDK

• Install Java ME: Follow the installation instructions for Java ME SDK.
• Configure PATH: Add the SDK's bin directory to your system's PATH.

Step 2: Write the Midlet Code

Create a new directory for your project, e.g., HelloJavaME. Inside it, create a new file named HelloMidlet.java and add the following code:

import javax.microedition.lcdui.*;
import javax.microedition.midlet.*;

public class HelloMidlet extends MIDlet {
    Display display;
    Form form;

    public HelloMidlet() {
        display = Display.getDisplay(this);

        form = new Form("Hello Midlet");
        form.append("Hello, Java ME World!");
    }

    protected void startApp() {
        display.setCurrent(form);
    }

    protected void pauseApp() {}

    protected void destroyApp(boolean unconditional) {}

    public void commandAction(Command c, Displayable d) {
        if (c.getCommandType() == Command.EXIT) {
            notifyDestroyed();
        }
    }
}

Step 3: Compile the Midlet Code

Use the midpjavac command to compile the code:

midpjavac -d bin src/HelloMidlet.java

This command generates HelloMidlet.class in the bin directory.

Step 4: Package the Midlet

Create a JAR file for the midlet:

jar -cvf HelloJavaME.jar -C bin .

Next, create a MIDlet suite (JAD) file. Create a file named HelloJavaME.jad with the following contents:

MIDlet-1: HelloMidlet, , HelloMidlet
MIDlet-Name: HelloJavaME
MIDlet-Vendor: Your Name
MIDlet-Version: 1.0
MIDlet-Jar-URL: HelloJavaME.jar
MIDlet-Jar-Size: 1000
MicroEdition-Configuration: CLDC-1.1
MicroEdition-Profile: MIDP-2.0

Step 5: Run the Midlet on the Emulator

Use the midp command to run the midlet:

midp HelloJavaME.jad

This command launches the Java ME emulator and displays the "Hello, Java ME World!" message.

Summary

• Java SE: Used for standard Java applications. Good for desktop applications, servers, and large-scale applications.
• Java EE: Used for enterprise applications. Ideal for web services, scalable web applications, and robust, secure applications.
• Java ME: Used for embedded and mobile applications. Suitable for devices with limited resources.