By now, you’ve probably written a fair amount of code as you have worked your way through the chapters. Chances are you have encountered an error or two while doing so. Some of these will be compile-time errors your development tool will have caught, so you can fix them as you work. Others will have surfaced only at run time, raising exceptions that result in an error page of some kind being displayed. As you build more complex applications, other types of errors creep in: logical errors. These kinds of errors won’t stop your application from running, but they will result in unpredictable behavior. Coding errors, whether they are simply typos or logical errors, are a fact of a developer’s life.