Greenfoot freezes as soon as I press Run

It compiled and it is still wrong

Greenfoot freezes as soon as I press Run

This page is part of Intro to Java with Greenfoot. It assumes you have reached lesson 1.6. Opening it is not counted against you and is not tracked as progress.

What it actually means

Something inside act() never finishes, so Greenfoot never gets the chance to draw the next frame.

The usual causes

Ranked by how often each one turns out to be the answer. Work down the list.

  1. A while (true) loop inside act(). This is by far the most common cause.
  2. A loop whose condition can never become false.
  3. A method that calls itself with no stopping case.

How to fix it

Force-quit Greenfoot, reopen it, and look inside act() for a loop. act() must FINISH every frame. Delete the loop: act() is already the repetition, so one small step per frame is all you need.

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