Question

I’ve got my ‘virtual list’ in swing working well, but it seems to fail when I exceed some particular number of items. By ‘fail’ I mean that the scroll bar magically vanishes when the number of items is > Nmax, and it comes back when the number of items is <= Nmax; Nmax seems to be somewhere around 119,304,000 on my system.

What am I running up against?!?!

(Here’s a test program: on my computer, if I type in 119,304 it works ok, but I click the up arrow and the scroll bar disappears)

package com.example.test;  import java.awt.BorderLayout; import java.awt.Dimension; import javax.swing.AbstractListModel; import javax.swing.JFrame; import javax.swing.JLabel; import javax.swing.JList; import javax.swing.JPanel; import javax.swing.JScrollPane; import javax.swing.JSpinner; import javax.swing.SpinnerModel; import javax.swing.SpinnerNumberModel; import javax.swing.event.ChangeEvent; import javax.swing.event.ChangeListener;  // based on: // http://www.java2s.com/Tutorial/Java/0240__Swing/extendsAbstractListModel.htm // http://www.java2s.com/Tutorial/Java/0240__Swing/SpinnerNumberModel.htm // http://java.sun.com/j2se/1.4.2/docs/api/javax/swing/SpinnerNumberModel.html // http://www.java2s.com/Tutorial/Java/0240__Swing/ListeningforJSpinnerEventswithaChangeListener.htm // http://java.sun.com/products/jfc/tsc/tech_topics/jlist_1/jlist.html  public class BigVirtualList extends JFrame {      public static void main(String[] args) {         new BigVirtualList();     }      static final int initialLength = 1;     final private JList list1 = new JList();     final private BVLData bvldata = new BVLData(initialLength*1000);      public BigVirtualList() {         this.setTitle('Big virtual list');         this.getContentPane().setLayout(new BorderLayout());         this.setSize(new Dimension(400, 300));         list1.setModel(bvldata);          list1.setPrototypeCellValue(list1.getModel().getElementAt(0));           SpinnerModel model1 = new SpinnerNumberModel(initialLength,1,1000000,1);         final JSpinner spinner1 = new JSpinner(model1);          this.getContentPane().add(new JScrollPane(list1), BorderLayout.CENTER);         JLabel label1 = new JLabel('Length (1000s of items):');         JPanel panel1 = new JPanel(new BorderLayout());         panel1.add(label1, BorderLayout.WEST);         panel1.add(spinner1, BorderLayout.CENTER);         this.getContentPane().add(panel1, BorderLayout.SOUTH);                ChangeListener listener = new ChangeListener() {             public void stateChanged(ChangeEvent e) {                 Integer newLength = (Integer)spinner1.getValue();                 bvldata.setLength(newLength*1000);             }         };          spinner1.addChangeListener(listener);         setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);         setVisible(true);     } }  class BVLData extends AbstractListModel {     public BVLData(int length) { this.length = length; }      private int length;      public int getLength() { return length; }     public void setLength(int length) {         int oldLength = getLength();         this.length = length;         int newLength = getLength();          if (newLength > oldLength)             fireIntervalAdded(this, oldLength+1, newLength);         else if (newLength < oldLength)             fireIntervalRemoved(this, newLength+1, oldLength);           }         @Override     public Object getElementAt(int index) {         return 'Item '+index+' mod 107 = '+(index%107);     }      @Override     public int getSize() { return getLength(); }  } 

Answer 1

Well I don’t see the purpose but anyway …

I guess you break the integer max value somewhere in the scroll pane:

System.out.println('CellHeight:'+list1.getFixedCellHeight()); System.out.println('CellHeight*119304000:'+NumberFormat.getNumberInstance().format(list1.getFixedCellHeight()*119304000.0)); System.out.println('MAXINT:'+Integer.MAX_VALUE); 

Gives you the numbers:

 CellHeight:18 CellHeight*119304000:2.147.472.000 MAXINT:2.147.483.647 

As you can see adding another 18000 pixel in height will go beyond MAXINT … this gets you in trouble.