Explore a Simple Debugging Puzzle | Force.com IDE Developer Guide

Create Sample Accounts in Your Org
To complete this exercise, add the following sample data in your org.

Create an Apex Class
Next, let’s create an Apex class to debug. This class removes cold accounts from a list so that you can focus on more promising clients.

Create a Visualforce Page
Now we need a Visualforce page to bring the AccountViewer controller to life.

Identify a Problem
Because we never write buggy code, our Visualforce page should be working perfectly! Let’s make sure.

Debug the Problem
Let’s use the Apex Debugger to see what went wrong.

Fix the Problem
By now you’ve discovered how to fix the problem in AccountViewerController.cls. But you can’t save changes to code while a debugging session is in process. Terminate the debugging session, and then fix the code.

Delete Your Sample Accounts
Unless you want to keep your sample accounts so that you can play with them in the future, run this code to delete them.