Java Getting Started

Java Install

Some PCs might have Java already installed.

To check if you have Java installed on a Windows PC, search in the start bar for Java or type the following in Command Prompt (cmd.exe):

 

If Java is installed, you will see something like this (depending on version):

 

If you do not have Java installed on your computer, you can download it for free at oracle.com.

Note: In this tutorial, we will write Java code in a text editor. However, it is possible to write Java in an Integrated Development Environment, such as IntelliJ IDEA, Netbeans or Eclipse, which are particularly useful when managing larger collections of Java files.

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Setup For Windows

To install Java on Windows:

1. Go to "System Properties" (Can be found on Control Panel > System and Security > System > Advanced System Settings)
2. Click on the "Environment variables" button under the "Advanced" tab
3. Then, select the "Path" variable in System variables and click on the "Edit" button
4. Click on the "New" button and add the path where Java is installed, followed by \bin. By default, Java is installed in C:\Program Files\Java\jdk-11.0.1 (If nothing else was specified when you installed it). In that case, You will have to add a new path with: C:\Program Files\Java\jdk-11.0.1\bin
   Then, click "OK", and save the settings
5. At last, open Command Prompt (cmd.exe) and type java -version to see if Java is running on your machine

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Java Quickstart

1. Writing the Java Code:

   • You begin by creating a Java file named Main.java. In Java, every application starts with a class definition, and the class name must match the filename.
   • Inside Main.java, you define a class named Main with a main method. The main method is the entry point for Java applications and serves as the starting point for execution.
   • Within the main method, you use the System.out.println() method to print the "Hello World" message to the console.

2. Compiling the Java Code:

   • After saving Main.java, you open the Command Prompt and navigate to the directory where the file is saved.
   • You use the javac command to compile the Java source code. In this case, you run javac Main.java. If there are no errors in the code, the compiler will generate a bytecode file named Main.class.

3. Running the Java Program:

   • Once the code is successfully compiled, you use the java command to execute the program. You type java Main in the Command Prompt.
   • The Java Virtual Machine (JVM) loads the bytecode from Main.class and starts executing the main method.
   • As a result, the "Hello World" message is printed to the console, indicating that the program has run successfully.

Main.java

 

 

Don't worry if you don't understand the code above - we will discuss it in detail in later chapters. For now, focus on how to run the code above.

Save the code in Notepad as "Main.java". Open Command Prompt (cmd.exe), navigate to the directory where you saved your file, and type "javac Main.java":

 

This will compile your code. If there are no errors in the code, the command prompt will take you to the next line. Now, type "java Main" to run the file:
 

 

The output should read:

 

Congratulations! You have written and executed your first Java program.


 

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