What's the meaning about this square frame around the “null” in eclipse

Question

I'm newbie in eclipse, what's this square frame around the "null" means.

Answer 1

That looks like an editing box. Sometimes when you do things like inserting code from a template or letting Eclipse add unimplemented abstract methods it will put these edit boxes around the default values that you're likely to change. If you click on it and hit enter it should go away.