Question

Why does public void printStackTrace(PrintStream s) in the Throwable class take a PrintWriter, instead of a Writer?

I think Writer should be the norm (code to the interface, not a specific implementation), but it could be something that I’m missing, hence this question.

Answer 1

Writer is an abstract class which PrintWriter extends. Throwable.printStackTrace takes a PrintWriter because it calls the println method on it which is not available in the Writer class.println is called because it needs to print the stack trace, one stack frame per line.