Compiling and running a Java application on Mac OSX, or any major operating system, is very easy. Apple includes a fully-functional Java runtime and development environment out-of-the-box with OSX, so all you have to do is write a Java program and use the built-in tools to compile and run it.

Writing Your First Program

The first step is writing a simple Java program. Open up a text editor (the built-in TextEdit app works fine), type in the following code, and save the file as "HelloWorld.java" in your home directory.

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

For example, if your username is David, save it as "/Users/David/HelloWorld.java". This simple program declares a single class called HelloWorld, with a single method called main. The main method is special in Java, because it is the method the Java runtime will attempt to call when you tell it to execute your program. Think of it as a starting point for your program. The System.out.println() method will print a line of text to the screen, "Hello World!" in this example.

Using the Compiler

Now that you have written a simple Java program, you need to compile it. Run the Terminal app, which is located in "Applications/Utilities/Terminal.app". Type the following commands into the terminal:

cd ~
javac HelloWorld.java

You just compiled your first Java application, albeit a simple one, on OSX. The process of compiling will produce a single file, called "HelloWorld.class". This file contains Java byte codes, which are the instructions that the Java Virtual Machine understands.

Running Your Program

To run the program, type the following command in the terminal.

java HelloWorld

This command will start a Java Virtual Machine and attempt to load the class called HelloWorld. Once it loads that class, it will execute the main method I mentioned earlier. You should see "Hello World!" printed in the terminal window. That's all there is to it.

As a side note, TextWrangler is just a text editor for OSX and has no bearing on this situation. You can use it as your text editor in this example, but it is certainly not necessary.

I suspect the problem you have is the path used to find your executables. It depends also if you use an OSX app or a unix cmd

If a unix cmd (or use the Unix part of an OSX app e.g. /Applications/AppName.app/Contents/MacOS/AppName) then there are two ways to fix this

1. Put the full path to the executable in the Java code e.g.
   String[] cmd = {"/full/absolute/path/to/love", "/Users/mtc06/testgame"};

2. Alter the path to include the executable. This depends on the method java is launched.

a)If java is run from the command line then add the directory of the executable to the PATH environment variable.
b) For old versions of OSX and if the java program is run from the Finder the path has to be altered in ~/MacOSX/environment.plist e.g. adding /Users/mark/bin

   <?xml version="1.0" encoding="UTF-8"?>
   <!DOCTYPE plist PUBLIC "-//Apple Computer//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
   <plist version="1.0">
   <dict>
      <key>PATH</key>
      <string>/Users/mark/bin:/usr/local/bin:/bin:/usr/bin:/sbin:/usr/sbin:/usr/X11R6/bin:/usr/libexec/binutils:</string>
   </dict>
   </plist>

If the app is an OSX app the you need to launch it using open so the command line is

open -a love.app "/Users/mtc06/testgame"  

so Java command is (not tested)

String[] cmd = {"/usr/bin/open", "-a" , "love.app",  "/Users/mtc06/testgame"};

Open the terminal, go to the directory where the file is located and do this:

javac -classpath . name.java // compile the code
java name                    // run the program

Of course, both javac and java must be available in the operating system's PATH variable, but in a Mac that's already configured.

To entirely use a (bash) shell to install e.g. Java 8u112 JRE do the following:

Download:

cd ~/Downloads
curl -v -j -k -L -H "Cookie: oraclelicense=accept-securebackup-cookie" http://download.oracle.com/otn-pub/java/jdk/8u112-b15/jre-8u112-macosx-x64.dmg > jre-8u112-macosx-x64.dmg

Mount:

hdiutil attach jre-8u112-macosx-x64.dmg

Install:

sudo installer -pkg /Volumes/Java\ 8\ Update\ 112/Java\ 8\ Update\ 112.app/Contents/Resources/JavaAppletPlugin.pkg -target /

Clean-up:

diskutil umount /Volumes/Java\ 8\ Update\ 112 
rm jre-8u112-macosx-x64.dmg

To install the latest Oracle JDK (at the time of writing this answer it's Java 8u121 JDK) the various paths (besides the version number) are slightly different compared to the older JRE version. The URL contains an additional directory (i.e. /e9e7ea248e2c4826b92b3f075a80e441) and the dmg file contains a .pkg file instead of an installer app:

cd ~/Downloads
curl -v -j -k -L -H "Cookie: oraclelicense=accept-securebackup-cookie" http://download.oracle.com/otn-pub/java/jdk/8u121-b13/e9e7ea248e2c4826b92b3f075a80e441/jdk-8u121-macosx-x64.dmg > jdk-8u121-macosx-x64.dmg
hdiutil attach jdk-8u121-macosx-x64.dmg
sudo installer -pkg /Volumes/JDK\ 8\ Update\ 121/JDK\ 8\ Update\ 121.pkg -target /
diskutil umount /Volumes/JDK\ 8\ Update\ 121
rm jdk-8u121-macosx-x64.dmg

First you need to compile the program to a .class file using javac.

javac src/ch/idsia/scenarios/Play.java

Then execute the .class file created (Note - Without the .java or .class extension)

java src/ch/idsia/scenarios/Play 

Ref - Documentation on Compiling

Compiling the Program

A program has to be converted to a form the Java VM can understand so any computer with a Java VM can interpret and run the program. Compiling a Java program means taking the programmer-readable text in your program file (also called source code) and converting it to bytecodes, which are platform-independent instructions for the Java VM.

cd into the directory in which your Calculator.java file is stored, run

javac Calculator.java

this will create a file Calculator.class. You can now run the compiled class with

java Calculator

mind that there is no .class to be added!