jar' exactly like that without the quotation marks. Go to Browse for opening the File Explorer window. I've looked online, but I couldn't find many plausible alternatives for Mac. Once you have found the file, select it and click Ok. Clicking on ‘Close’ will save the changes. For instance, you could also use “-Xmx1024M” or “-Xmx256M”, if you had more or less memory to spare. I have downloaded RL Craft but when I click 'Play' nothing happens. In the case of the Java Sound Demo, the file JavaSoundDemo. The JDK will be installed at the following directories. jar', but when I run it I get the following alert: 'The jar file 'MoparScape. jar no main manifest attribute, in /path/to/game. The launcher continues to work with all earlier versions of Minecraft, and was working with Minecraft 1. 6 version of Java that use to be included with OS X. Jar launcher mac not working To make the jar file executable, the manifest must include the name of the Main class file.