从Java JTextArea读取

Question

Okay, thus may seen kind of odd, but I wanted to get some suggestions from everyone here. I am a beginning Java developer (after 2 years of ASP.NET web development) and I have recently began working on my first Java project - a calculator. I realize that their are tons of calculators out there, but I thought it would be a good beginner project.

Anyway, here is what I need help with. Currently, I am using a Scrolling JTextArea for display (instead of a simple JTextField) that is approximately 5 rows tall. I want the user to be able to scroll through the list to see previous entries and such. The format of the box will be equation on one line and the program will generate the answer on the next and so on.

My real question is, how is the best way to implement this? My fist idea was to read through the JTextArea when equals is pressed, down to the last line and try to search that line for the operator (+, -, etc.) and the operands. Is this the best way to go about this? Although, this would work would work, I think it could get cumbersome and sounds very inefficient. I am open to any suggestions, even possibly replacing the JTextArea is some other component would work better.

Thanks!

Answer 1

There's no need to read through the JTextArea contents - use JTextArea.append() to add to the end. Here are some examples of JTextArea content manipulation:

JTextArea ta = new JTextArea("Initial Text");

// Insert some text at the beginning
int pos = 0;
ta.insert("some text", pos);

// Insert some text after the 5th character
pos = 5;
ta.insert("some text", pos);

// Append some text
ta.append("some text");

// Replace the first 3 characters with some text
int start = 0;
int end = 3;
ta.replaceRange("new text", start, end);

// Delete the first 5 characters
start = 0;
end = 5;
ta.replaceRange(null, start, end);

Answer 2

If you are open to different interfaces, you might want to try something like a JTextField at the top of your view, from which you can receive as input your 'new' inputted equation, and then below it with the same width a JList that would scroll to have all of the previous equations and their results. That would make parsing of the current formula much easier, and you would also have an easy time of keeping your previous formula and their results in a scrollable list, with the easy option of keeping the most recent on top.

Answer 3

your idea is interesting. so you would have a line such as.

2+2

then when pressing calculate would add the line

4

and so on then you could type in another equation.

it could work but as you said it wouldn't be the most efficient implementation... but that's just a tradeoff of getting the desired functionality.

If i were going to implement it the way you discribed (with a JTextArea) I'd use scanner, and scan the value string a line at a time.

if the line has +/- in it then do the calculation and add both the original line and the answer to a string.

the new string is the new value of the text field.

this method would get pretty cumbersom as you would be continually recalculating the users old entries more were added.

I guess if you continually stored the last line of the document, when you run out of lines, calculate the last stored and append the answer, then it wouldn't be so bad.

---

Here's what I would do:

use a JTextField to enter in the calculations, and a JList to display the old ones and their answers.

Answer 4

You could treat each line as a single operation. That way you could use the String array returned directly by:

String [] operations = textArea.getText().split("\n");

And then you'll know that exactly each one of them as a complete operation ( may be invalid, but that' another story )

Is this what you asked or do I totally misread you?

Answer 5

I think a simpler solution would actually use two components. A TextArea to hold the "history" of what's happened so far, and a textfield where the user inputs new entries.

Answer 6

Thanks to everyone who replied. You all gave me some ideas to think about. I think right now, I am going to go with my original idea of using a single JTextArea and try to find ways to optimize the process. If that gets too difficult (which is very possible), I will follow the majority's advice and use two separate fields. Thanks for replying everyone!