Java Installation and Setup (JDK)

What you need to install

To write and run Java, you install the JDK (Java Development Kit). It contains the compiler javac (to turn your code into bytecode) and the JVM (to run it). Once the JDK is installed and set up, you can compile and run Java programs from the command line.

Download the JDK

1. Go to Oracle's Java download page, or get a free build like OpenJDK.
2. Choose the version for your operating system (Windows, Mac or Linux).
3. Run the installer and follow the steps.

Any recent long-term-support (LTS) version, like Java 17 or 21, is a good choice for learning.

Setting the PATH

On Windows, after installing, add the JDK's bin folder to the system PATH so the command line can find javac and java.

Check the version

Open the command line and run both commands:

java -version
javac -version

If both show a version number, the JDK is installed and your PATH is correct. If javac is not found, revisit the PATH step.

Compile and run a program

Save this as Hello.java:

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

Then in the command line, in that folder:

javac Hello.java   // compile -> makes Hello.class
java Hello         // run (no .class)

javac compiles your code to bytecode (Hello.class), and java Hello runs it on the JVM. Note the file name must match the public class name.

Using an IDE

The command line is great for learning, but an IDE makes real work easier:

• IntelliJ IDEA — very popular, has a free Community edition.
• Eclipse — long-standing free IDE for Java.
• VS Code — lightweight, with a Java extension pack.

IDEs add autocomplete, error highlighting and one-click run, so start with one once you are comfortable with the basics.

Common mistakes

• Installing only the JRE. You need the JDK to compile with javac.
• Forgetting the PATH. Then javac/java are "not recognised".
• File name mismatch. The file must match the public class name (Hello.java for class Hello).
• Adding .class when running. Use java Hello, not java Hello.class.

Summary

• Install the JDK — it has the compiler and the JVM.
• Set the PATH so javac and java work anywhere.
• Check with java -version and javac -version.
• Compile with javac File.java, run with java File.
• Use an IDE like IntelliJ or VS Code for real projects.

Next, write your first program in Hello World in Java, or learn the parts in JDK, JRE and JVM.