Java Setup for MacOS

A beginner’s Java development environment setup for MacOS

Franco Posa

1. Install Java with Homebrew

Install OpenJDK

With a preference towards FOSS, we are going to use OpenJDK over Oracle’s Java SE JDK or other proprietary options.

% brew install openjdk

Make sure Java from the OpenJDK is first in your PATH

Add the following to your .zshrc:

export PATH="/usr/local/opt/openjdk/bin:$PATH"

Confirm your java and javac commands map to the OpenJDK

% which java
/usr/local/opt/openjdk/bin/java

% which javac
/usr/local/opt/openjdk/bin/javac

% java --version
openjdk 13.0.2 2020-01-14
OpenJDK Runtime Environment (build 13.0.2+8)
OpenJDK 64-Bit Server VM (build 13.0.2+8, mixed mode, sharing)

2. Hello Java

Create HelloWorld.java in your preferred editor:

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

Compile your code:

This will create the HelloWorld.class file containing the Java bytecode compiled for the JVM.

% javac HelloWorld.java

Bonus: the Java bytecode in the HelloWorld.class file is in a binary format that will not be readable with most text editors, but, you can use the javap class file disassembler command. This is not much use to us at this point, but it is pretty interesting.

% javap -c HelloWorld
Compiled from "HelloWorld.java"
public class HelloWorld {
  public HelloWorld();
    Code:
       0: aload_0
       1: invokespecial #1                  // Method java/lang/Object."<init>":()V
       4: return

  public static void main(java.lang.String[]);
    Code:
       0: getstatic     #7                  // Field java/lang/System.out:Ljava/io/PrintStream;
       3: ldc           #13                 // String Hello, World
       5: invokevirtual #15                 // Method java/io/PrintStream.println:(Ljava/lang/String;)V
       8: return
}

Run your code

Using java command, point the -classpath/-cp argument to the location of the class file and provide the name of the class whose main method should be run.

% java -classpath . HelloWorld
Hello, World

Run your code without the .class file

More recent Java versions support running single Java files without the intermediate javac command for compiling to a class file. The compilation step still occurs, but the JVM bytecode is held in memory instead of written to the disk.

The limitation to a single file will not make this very useful for running an application but it is nice to speed up running scratch files or single-file programs while leaving fewer unwanted class files in your working directory.

% java HelloWorld.java 
Hello, World