1. Getting Started with Java

1. Downloading Java SE
   • Download Java SE (details vary depending on version) :
     • https://www.oracle.com/technetwork/java/javase/downloads/index.html

     

2. Installing Java SE
   • Select and run the appropriate JDK installation
     • E.g. jdk-7u51-windows-x64.exe
   • Accept all defaults during installation

   

3. Java SE Folder Structure
   • Default installation folder for Java SE (v1.7, update xx):
     • C:\Program Files\Java\jdk1.7.0_xx
   • Folder structure:

   

4. Minimalistic Development
   • Define a public Java class
     • Filename must be classname.java
       public class MyFirstApp {
 public static void main(String[] args) {
  System.out.println("Hello world");
 }
}

   • Compile the class from the command line
     • Using the Java compiler, javac.exe
     • Note, javac.exe must be on the path
     • Below will create MyFirstApp.class

     javac MyFirstApp.java


   • Run the class from the command line
     • Via the JVM, java.exe
     • Note, java.exe must be on the path
     • You specify the classname without the .class extension

     java MyFirstApp
Hello world


JAR files

1. Overview of JAR Files
   • In a real Java application, you’ll have lots of Java classes
     • Each class is compiled to a separate .class file
   • It’s common to bundle up all the classes etc… into a JAR file
     • Typically use the .jar file extension
     • The Java Archive (JAR) file format is a zip-file really
   • You can manage JAR files by using the jar.exe tool from the command line
     • Part of the JDK
2. How to Create a JAR File
   • To create a JAR file:
     jar cfm jar-file-name manifest-file-name input-file(s)

   • Here’s a description of the options:
     • c means you want to create a JAR file
     • f means you want the output to go to a file (rather than STDOUT)
     • m means you want to include a manifest file (see later)
   • And here’s a description of the file names:
     • jar-file-name is the name of the JAR file you want to create
     • manifest-file-name is the name of the manifest file (see later)
     • input-file(s) is a list of files to include in the JAR file
3. Example: Java Files
   • Let’s see how to create a JAR file containing 2 Java classes
     • See the DemoGettingStarted folder
   • Here’s the “main” Java class for the application:
     public class MyProg {
 public static void main(String[] args) {
  System.out.println("Hello from my program.");
  MyHelper.displayDateTime();
  System.out.println("Goodbye from my program.");
 }
}

   • View code file.
   • And here’s a “helper” Java class for the application:
     public class MyHelper {
 public static void displayDateTime() {
  System.out.println("It is now " + new java.util.Date());
 }
}

   • View code file.
4. Example: Specifying the Entry Point
   • If you have an application bundled in a JAR file, you need some way to indicate which class file is the entry point
     • You provide this information in a “manifest file”
     • Set the Main-Class property to the name of the main class
       Main-Class: MyProg

   • Notes:
     • You must specify the fully-qualified name of the class (including its package name – see later for more info about packages)
     • The manifest file must end in a new line or carriage return
5. Example: Creating the JAR File
   • First, compile the Java classes:
     javac MyProg.java MyHelper.java

   • Then create a JAR file containing the .class files and the manifest file:
     jar cfm MyFirstJarFile.jar manifest.txt MyProg.class MyHelper.class

6. How to Run a JAR’d Application
   • To run a JAR’d application:
     • Run java.exe to launch the Java Virtual Machine
     • Use the -jar option to indicate you want to run a JAR file
     • The JVM consults the manifest file to determine the main class
       java -jar MyFirstJarFile.jar
Hello from my program.
It is now Mon Feb 17 10:54:07 2014
Goodbye from my program.


Using an IDE

1. What Java IDE‘s are out there?
   • Popular Java IDEs:
     • Eclipse (we’ll be using this)
     • Oracle JDeveloper
     • IBM WebSphere Application Developer
     • NetBeans
     • Etc…
2. Downloading and Installing Eclipse
   • In a browser window:
     • Browse to https://www.eclipse.org/downloads
     • Click the Eclipse IDE for Java Developers product
   • In the next Web page:
     • Click the appropriate download link for your platform, e.g. Windows 64-bit
     • The download is a simple zip file
   • Unzip the Eclipse zip file
     • To the C:\ destination folder
     • Creates a folder named C:\eclipse
3. Starting Eclipse
   • Start Eclipse
     • i.e. run c:\eclipse\eclipse.exe
   • Eclipse prompts you for a workspace
     • The workspace is a folder that will contain all your Java projects
     • Specify C:\JavaWorkspace

     

4. Loading Existing Projects
   • You can load existing projects into the workspace

   

5. Creating a Java Project
   • You can create a new Java project

   

6. Adding a Class
   • You can add a new class to your project

   

7. Implementing the Class
   • Implement the class, e.g:
     package mypackage;
public class MyClass {
 
 public static void main(String[] args) {
  System.out.println("Eclipse says Hello!");
 }
}

   • View code file.
8. Running the Class
   • Run the class and see the output in the console window