Scanner input boxes wrap when Interaction scrollbar appears

short Java program to demonstrate this bug

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The problem is that the input box (which is a subclass of
JTextArea) has to be rectangular, so when the text gets too
long and the line in the Interactions Pane wraps, the entire
input box moves to the next line. The input box then fills
the available space in that new line and consumes the entire
width of the Interactions Pane, which makes it look like
there is a line break before the input box, even though
there isn't.

I think the optimal behavior that we can achieve is that the
input box remains on the line where it originally was and
only uses its original width, i.e. text that has wrapped to
the next line appears "indented"; the space beneath the text
to the left of the input box will remain empty.

To achieve this, I have tried to limit the maximum width of
the input box as returned by getMaximumSize(). This has
prevented the input box from consuming the entire width, but
as soon as it needs two lines of text, it still wraps to the
beginning of the next line. I don't know why, and I don't
know the Swing text document API well enough. It was lucky
enough to figure out how to fix the problem with the input
box disappearing when the user stepped through the program
with the debugger.

I would also like to point out that it will be impossible to
prevent the input box from being on the next line in all
cases: In the worst case, the text to the left of the input
box will consume the entire line except for one character.
If we want to prevent input boxes that are only a character
wide, we will have to set a minimum width, and in that case,
the text box will have to be on the next line.

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Mathias,

Thank you for your reply. I believe we are talking about
two different things. Your message was talking about the
case where the user input textbox appears and I type a very
long string into it. As you say, the textbox expands to a
second line. This seems like reasonable behavior and does
not bother me.

The case I'm describing is different. I'm talking about the
physical position of the textbox moving to the next line at
the moment where the overall interactions pane requires a
scrollbar. One way to reproduce this bug is to load DrJava
and type the following lines into the interactions pane:

import java.util.*;
Scanner c = new Scanner(System.in);
System.out.print("Input? "); s = c.nextLine();

Notice that the input box appears on the same line as the
"Input? " prompt. Now, without entering any text, resize
the interactions pane by dragging the vertical divider at
its top. Shrink the interactions pane to various sizes such
that its entire contents do not fit in the viewable area. A
scrollbar will appear on the right side of the interactions
pane (which is fine), but, the input textbox will jump to
the next line!

You might say, why should a person be resizing their
interactions pane while the program is running, anyway? But
the bug doesn't only occur when resizing. It also occurs if
you're running a program with several prompt/inputs, whose
output initially doesn't need as scrollbar but eventually
becomes long enough that it does. Suddenly, just as the
interactions pane scrollbar appears, all the previous input
textboxes wrap to the next line. This is undesirable
because it makes our students think they've inserted a stray
println statement or otherwise inserted an erroneous line break.

screenshot before wrapping occurs

screenshot after wrapping occurs

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That last post by "nobody" was me; I'd forgotten to log in.
I have now also attached two screenshots of the bug.

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Thanks for the detailed explanation; I understand the
problem now, even though I don't yet know how to fix it.

The input box somehow never shrinks. When the scrollbar
appears, the space becomes too small fo the input box, so it
wraps to the next line. There, it expands to fill the entire
width of the Interactions Pane, so even when the scrollbar
disappears, it remains too big and therefore on the next line.

Fixing the width to prevent the input box from expanding
beyond its original width helps a little bit: Input boxes
that were created when the scrollbar was visible stay in
their correct place, but those created when the scrollbar
was not there still move to the next line; however, if the
scrollbar disappears, they snap back to where they shou;d be.

I'll have to play around a little, but I'm confident we'll
have this problem removed pretty soon.

Thanks for helping us make DrJava better!

--Mathias

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We took the easy way out and simply configured the window to always include the scroll bar.

I am closing this bug.