[Setup] Java Development Environment

Java development requires the JDK (Java Development Kit). The JDK includes both the compiler (javac) and the runtime environment (java).

OS	Installation Method
Windows	Download and run the installer from Adoptium (formerly AdoptOpenJDK). Make sure to enable the option to add the environment variable PATH during installation.
macOS	Run brew install openjdk with Homebrew, or download the installer from Adoptium.

After installation, run the following in a terminal (Command Prompt on Windows) to verify.

javac --version
javac 21.0.3

java --version
openjdk 21.0.3

If both commands display a version number, the installation was successful.

Java is a compiled language. The process involves two steps: compiling the source code (.java) to bytecode (.class), and then running it.

Step	Command	Description
1	javac FileName.java	Compiles the source code and generates a .class file.
2	java ClassName	Runs the .class file (do not include the extension).

Save the following content as Hello.java using a text editor. The file name must match the class name. In this example the class is named Hello, so the file must be named Hello.java.

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

        String name = "Alice";
        System.out.println("Hello, " + name + "!");

        for (int i = 1; i <= 5; i++) {
            System.out.println("Loop iteration " + i);
        }
    }
}

Navigate to the folder where you saved the file in a terminal, then run the following commands in order.

Compile:

javac Hello.java

Run:

java Hello
Hello, Java!
Hello, Alice!
Loop iteration 1
Loop iteration 2
...

After a successful compilation, a Hello.class file is generated in the same folder.

If there is a mistake in the code, an error message is displayed when running javac. Here are some common errors.

Error	Cause
class Hello is public, should be declared in a file named Hello.java	The file name and class name do not match.
reached end of file while parsing	Curly braces ({ and }) are not properly matched.
cannot find symbol	There is a typo in a variable name or method name.
'; ' expected	A semicolon (;) is missing at the end of a statement.

Error messages include a line number. Check and fix the indicated line.

If the terminal shows javac: command not found or java: command not found, the PATH may not be configured correctly. Follow the steps below to check and set it up.

1. Locate the command

Check where the javac command is installed.

which javac

If it is not found, check the common installation paths.

ls /usr/local/bin/javac
ls /opt/homebrew/bin/javac

2. Check your shell

echo $SHELL

If the output is /bin/zsh, edit ~/.zshrc. If it is /bin/bash, edit ~/.bashrc.

3. Set JAVA_HOME and PATH

For Java, you need to set the JAVA_HOME environment variable in addition to PATH. Check the JDK installation path and configure both.

Check the JDK installation path on macOS.

/usr/libexec/java_home

For macOS (zsh) — set JAVA_HOME and PATH:

echo 'export JAVA_HOME=$(/usr/libexec/java_home)' >> ~/.zshrc
echo 'export PATH="$JAVA_HOME/bin:$PATH"' >> ~/.zshrc
source ~/.zshrc

For Linux (bash):

echo 'export JAVA_HOME=/usr/lib/jvm/java-21-openjdk' >> ~/.bashrc
echo 'export PATH="$JAVA_HOME/bin:$PATH"' >> ~/.bashrc
source ~/.bashrc

On Windows, configure the following under "System Properties" → "Environment Variables".

Variable Name	Example Value
JAVA_HOME	C:\Program Files\Eclipse Adoptium\jdk-21
Path (add)	%JAVA_HOME%\bin