|
|
Featured White Papers
Sponsored Links
-
Slow Apps? Overloaded DBMS? - FREE Download
FREE Download Feb 14 - March 7th Eliminate bottlenecks & maximize performance ScaleOut StateServer®
Make bad users behave by using JFC documents -- revisited
A reader asks for clarity on JFC documents; Java Q&A expert Tony Sintes responds
- Feedback
- Discuss
I just read your previous Java Q&A "Make Bad Users Behave by Using JFC Documents." Upon reading the insertString() method I was a little surprised to see that it checked only the offset at which characters were being inserted, not the length
of the document. I did a quick cut and paste and compiled the code. Sure enough: If you place the insertion point anywhere
but at the end of the text you can insert more than limit characters up until the insertion point reaches limit.
Also note that the main() method shown is missing an f.pack().
OK, that's not exactly a question. However, I thought it important to point out this reader's observations. It's also important
that I also address the observations.
Fixing the code
Let's look at the original code:
import javax.swing.text.*;
public class LimitDocument extends PlainDocument
{
private int limit;
public LimitDocument(int limit)
{
super();
setLimit(limit); // store the limit
}
public final int getLimit()
{
return limit;
}
public void insertString(int offset, String s, AttributeSet attributeSet)
throws BadLocationException
{
if(offset < limit) // if we haven't reached the limit, insert the string
{
super.insertString(offset,s,attributeSet);
} // otherwise, just lose the string
}
public final void setLimit(int newValue)
{
this.limit = newValue;
}
}
public static void main(String args[])
{
JFrame f = new JFrame("Limit Test");
JTextField text = new JTextField();
text.setDocument(new LimitDocument(10));
f.getContentPane().add(BorderLayout.NORTH,text);
f.show();
}
Sure enough: no f.pack()! And yes, I'm using the offset and not the string length.
First, let's fix the code:
import javax.swing.text.*;
public class LimitDocument extends PlainDocument
{
private int limit;
public LimitDocument(int limit)
{
super();
setLimit(limit); // store the limit
}
public final int getLimit()
{
return limit;
}
public void insertString(int offset, String s, AttributeSet attributeSet)
throws BadLocationException
{
int end = getEndPosition().getOffset() - 1; // get the position of where the string ends
StringBuffer sb = new StringBuffer(getText(0,end));
sb = sb.insert(offset,s);
String new_s = sb.toString();
if(new_s.length() >= limit)
{
new_s = new_s.substring(0,limit);
}
super.remove(0,end);
super.insertString(0,new_s,attributeSet);
}
public final void setLimit(int newValue)
{
this.limit = newValue;
}
}
public static void main(String args[])
{
JFrame f = new JFrame("Limit Test");
JTextField text = new JTextField();
text.setDocument(new LimitDocument(10));
f.getContentPane().add(BorderLayout.NORTH,text);
f.pack();
f.show();
}
Wow, quite a change from the old code. So what am I doing?
Each time we try to enter new text, I grab the preexisting text and throw it in a StringBuffer. Using the offset, I then insert the new text into the old buffer. Finally, I grab the new string, truncate it if necessary,
clear the old text, and write the new string.
As more requirements are added, the code becomes a bit more complex. The question in the previous column simply asked how to limit what is typed in, not what is pasted in. Pasting makes the answer much more complicated.
- Feedback
Resources
- "Make Bad Users Behave by Using JFC Documents," by Tony Sintes (JavaWorld, May 2000), from which this question arose, can be found by going to
http://www.javaworld.com/javaqa/2000-05/02-qa-0512-textbox.html - Want more? See the Java Q&A Index for the full Q&A catalog
http://www.javaworld.com/javaworld/javaqa/javaqa-index.html
About Us | Advertise | Contact Us | Terms of Service/Privacy
Copyright, 2006-2010 Infoworld, Inc. All rights reserved.