Name: mc57594 Date: 12/05/99


java version "1.3.0"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.3.0-I)
Java HotSpot(TM) Client VM (build 1.3-I, mixed mode)


I have a JTextArea in a JScrollPane. What I need to do is change the text
in the text area and then scroll to a point. If the difference in the length
of the text in the text area is big, things don't work right.

Reason:
The maximum size is first updated incorrectly. This negates the setValue
call as it will be reduced to a value less than the max. This also
disallows the setting the max manually, as it will also be overwritten.

Since this all happens in a procedure that is queued on the
EventDispatchThread,
it is much more complicated to get around. However, the setValue call
seems to work well if the errant maximum value does not get in the way.

As I was looking at how things actually happen in the scrollbar, another
inconsistency arose.

Running the sample program the following output is obtained:

Max = 0 New Max = 1717
Firing state changed to 3 listener(s).
Max = 1717 New Max = 1717
-------------------
Max = 1717 New Max = 1717
setText
scrollToValue
setValue: 3000
Max = 1717 New Max = 1717
Firing state changed to 3 listener(s).
Max = 3000 New Max = 1717
Firing state changed to 3 listener(s).
Max = 1717 New Max = 1717
Max = 1717 New Max = 17017
Firing state changed to 3 listener(s).
Max = 17017 New Max = 17017
Max = 17017 New Max = 17017
Firing state changed to 3 listener(s).

Issue 1:
The call to set a value greater than the max has an affect on the maximum
value. This is directly from the setRangeProperties() method the
DefaultBoundedRangeModel. I don't know if this was intentional or not.
There is an identical issue with the minumum value.

Issue 2:
Even though the call to update the text in the textArea has completed,
the max is still set back to the old value before it is set with the new
value.

It is issue 2 that is standing in my way. However, if it was not for Issue 1,
I would have not so easily seen that the max value is actually getting SET to
an older value. It is not just being ignored, but being set.

Conversely, issue 2 keeps issue 1 from being a problem, since the errant value
is not around for very long.

The behaviour also exists in:
java version "1.2.2"
HotSpot VM (1.0fcs, mixed mode, build E)

The program below demostrates the behaviour. JScrollPane is subclassed to
allow for a different BoundedRangeModel. The DBoundedRangeModel is virtually
identical to the DefaultBoundedRangeModel (of 1.2.2) except for the debug
output.

CODE:
-----------------
import javax.swing.event.*;
import javax.swing.*;
import java.awt.event.*;
import java.awt.*;

public class SunTest21 extends JFrame {

private String smallText;
private String largeText;
private JTextArea textArea;
private boolean small = true;
private DScrollPane scrollPane;
private JScrollBar verticalScrollBar;

public static void main(String[] args) {
SunTest21 s = new SunTest21();
s.setSize(600,400);
s.setVisible(true);
s.addWindowListener( new WindowAdapter() {
public void windowClosing(WindowEvent e) {
System.exit(0);
}
});
System.out.println("-------------------");
}
public SunTest21() {
StringBuffer sb;
sb = new StringBuffer(1400);
for (int i = 0; i < 100; i++)
sb.append("Small Text.\n");
smallText = sb.toString();

sb = new StringBuffer(14000);
for (int i = 0; i < 1000; i++)
sb.append("Large Text.\n");
largeText = sb.toString();

Container cp = getContentPane();
cp.setLayout(new BorderLayout());
JPanel p = new JPanel();
JButton b = new JButton("Switch");
b.addActionListener( new ActionListener() {
public void actionPerformed(ActionEvent e) {
if (small) {
setText(largeText);
small = false;
scrollToValue(3000);
}
else {
setText(smallText);
small = true;
scrollToValue(1000);
}
}
});

p.add(b);
cp.add(p,BorderLayout.NORTH);

textArea = new JTextArea();
textArea.setText(smallText);
textArea.setLineWrap(true);
textArea.setWrapStyleWord(true);
scrollPane = new DScrollPane
(textArea,DScrollPane.VERTICAL_SCROLLBAR_ALWAYS,DScrollPane.HORIZONTAL_SCROLLBAR
_ALWAYS);
verticalScrollBar = scrollPane.getVerticalScrollBar();
cp.add(scrollPane,BorderLayout.CENTER);

}
private void setText(String s) {
System.out.println("setText");
textArea.setText(s);
}
private void scrollToValue(int value) {
System.out.println("scrollToValue");
verticalScrollBar.setValue(value);
}
private static class DBoundedRangeModel implements BoundedRangeModel {
private ChangeEvent changeEvent;
private EventListenerList changeListeners;

private int value, extent, min, max;
private boolean isAdjusting = false;

public DBoundedRangeModel() {
changeListeners = new EventListenerList();
}
public void setMinimum(int newMin) {
setRangeProperties(value,extent,newMin,max,isAdjusting);
}
public void setMaximum(int newMax) {
System.out.println("setMaximum: " + newMax);
//Thread.dumpStack();
setRangeProperties(value,extent,min,newMax,isAdjusting);
}
public void setValueIsAdjusting(boolean adjusting) {
setRangeProperties(value,extent,min,max,adjusting);
}
public void setExtent(int newExtent) {
setRangeProperties(value,newExtent,min,max,isAdjusting);
}
public void setValue(int newValue) {
System.out.println("setValue: " + newValue);
setRangeProperties(newValue,extent,min,max,isAdjusting);
}
public void setRangeProperties(int newValue, int newExtent, int
newMin, int newMax, boolean adjusting) {
System.out.println("Max = " + max + " New Max = " +
newMax );
//Thread.dumpStack();
if (newMin > newMax)
newMin = newMax;

//Is this correct?
if (newValue > newMax)
newMax = newValue;

//Is this correct?
if (newValue < newMin)
newMin = newValue;

if (((long)newExtent + (long)newValue) > newMax)
newExtent = newMax - newValue;
if (newExtent < 0)
newExtent = 0;
            
/*
System.out.print( "\t\t\t" + !(newValue == value) );
System.out.print(" " + !(newExtent == extent));
System.out.print(" " + !(newMin == min));
System.out.print(" " + !(newMax == max));
System.out.println(" " + !(adjusting == isAdjusting));
*/

boolean isChange =
(newValue != value) ||
(newExtent != extent) ||
(newMin != min) ||
(newMax != max) ||
(adjusting != isAdjusting);

if (isChange) {
value = newValue;
extent = newExtent;
min = newMin;
max = newMax;
isAdjusting = adjusting;

fireStateChanged();
}
}
public int getValue() {
return value;
}
public int getExtent() {
return extent;
}
public int getMaximum() {
//System.out.println("getMaximum: " + max);
return max;
}
public int getMinimum() {
return min;
}
public boolean getValueIsAdjusting() {
return isAdjusting;
}
public void addChangeListener(ChangeListener l) {
changeListeners.add(ChangeListener.class, l);
}
public void removeChangeListener(ChangeListener l) {
changeListeners.remove(ChangeListener.class, l);
}
protected void fireStateChanged() {
Object[] listeners = changeListeners.getListenerList();
System.out.println("Firing state changed to " + (
listeners.length / 2) + " listener(s).");
for (int i = listeners.length - 2; i >= 0; i -= 2 ) {
if (listeners[i] == ChangeListener.class) {
if (changeEvent == null)
changeEvent = new ChangeEvent
(this);
((ChangeListener)listeners
[i+1]).stateChanged(changeEvent);
}
}
}
}
private static class DScrollPane extends JScrollPane {
public DScrollPane(Component c, int vp, int hp) {
super(c,vp,hp);
}
public JScrollBar createVerticalScrollBar() {
DBoundedRangeModel m = new DBoundedRangeModel();
JScrollBar sb = new JScrollBar(JScrollBar.VERTICAL);
sb.setModel(m);
return sb;
}
}
}
(Review ID: 97581)
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