How to run minecraft in Debug mode

Question

I'm not even sure if you can ask this question here but i have the MCP which decompiles minecrafts code and allows you to edit it using eclipse. As you may know in Eclipse there is a feature called debug mode, whenever i click it, it says in the console.

Error: Could not find or load main class Start
Java HotSpot(TM) 64-Bit Server VM warning: Using incremental CMS is deprecated and will likely be removed in a future release

I went to the Start.java file and tried the debug button again but it didnt work so i was just wondering if you guy's know any way around it, The MCP is for 1.7.10 and it's default not Minecraft Forge. If this is not the right place to ask just ignore it. `

Answer 1

Making my comment an answer and adding the details you asked for:

Make sure that Start.java 's folder is defined as a source folder of the Eclipse project into which you imported Minecraft:

1. Right-click the project in Project Explorer view.
2. From the popup menu choose Build Path --> Configure Build Path... .
3. In the popup dialog, if the source tab on the right pane isn't chosen - choose it.
4. If your source folder already appears on the folder list Source folders on build path - this isn't the problem. Otherwise -
5. Click Add Folder... .
6. In the popup Source Folder Selection dialog, select your source folder and click OK .
7. Click OK in the former dialog.
8. Wait for Eclipse to rebuild your project.
9. Run your main class again and see what happens.