Problem scenario
You are using Eclipse for the first time. You try to to use Run, but you get an error message like this: "Unable to Launch The selection cannot be launched, and there are no recent launches." Or you try to go to "Run configuration" and you have a prototype, but the "Run" button is grayed out. What should you do?
Solution
In the Run configuration section, under the Java Application section on the left, is there a configuration? A prototype is not enough. Right click "Java Application" to create a configuration. Make sure the "Main" tab's "Main class" has something valid. Now the "Run" button should appear. You should be able to run code now.