Illegal argument coloring
Typing code is a tedious job that has to be done right. But we all make mistakes and the sooner we are alerted of mistakes the fewer compiler errors we get.

In the JBuilder IDE Options dialog (Tools | IDE Options...) we can see a tab page named Colors. This page let's us define different colors for different elements in our Java source code. For example Java identifiers can have a different font style or size or color.

At the bottom of the element listbox we can see the item Illegal. This element occurs when for example we are using a class reference which isn't in scope, because we didn't include it in the import statement. If we change the color settings of this element to some bright and obvious colors, we can see these type of errors immediately instead of waiting for the compiler error.

The following screenshot shows that the class reference to Button isn't in scope.