An common alternative to using an Integrated Development Environment (see IDEs) is to use a text editor, then compile and run the program using Sun's Java Software Development Kit (SDK). Many programming editors provide some means of compiling and running Java programs from within the editor.
Set the line number option and tabs to 4 spaces (Configure: Preferences: Document Classes: Java: Tabulation).
Turning runtime assertion checking on in TextPad
Configure > Preferences... > Tools > Run Java Application.
Set the value in the Parameters text field to
-ea $BaseName .
"-ea" is the abbreviation for Enable Assertions.
License: Nagware. You can use the full editor for free,
but you will see reminders to pay.