Setting the scrollbar to be by default in the middle of the scrollpane

Question

I was wondering if there was a way to set the JScrollBar to be at the middle of the scrollpane by default. I have a handle to the scrollbar and can determine the min and max of it's range, but I don't see a place to set the scrollbar position.

Answer 1

This is a runnable stand-alone app.
import java.awt.event.WindowEvent;
import java.awt.event.WindowListener;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.Dimension;
import java.awt.FlowLayout;
import java.awt.Component;
import java.awt.Color;
import java.awt.Font;
import javax.swing.*;
import javax.swing.table.*;
import java.util.*;
public class MarketBook extends JFrame implements WindowListener,
                                                  ActionListener{
     protected final int ROW_HEIGHT = 15;
     protected final int NUM_ROW = 14;
     protected final int PREF_WIDTH = 200;
     protected final int PREF_HEIGHT = 150;
     protected final int BID_COL = 1;
     protected final int OFFER_COL = 2;
     private String instrument;
     private String mkbkID;
     private String[] instArray = {"Item1", "Item2", "Item3"};
     private String[] colNames = {"Qty", "Bid", "Offer", "Qty"};
     private Vector<String> instrumentsList = new Vector<String>();
     private DefaultTableModel dm = new DefaultTableModel(colNames, NUM_ROW);
     private DefaultTableCellRenderer renderer = new DefaultTableCellRenderer();
     JPanel contentPane = new JPanel();
     JPanel topPanel = new JPanel();
     JComboBox instList = new JComboBox(instArray);
     JTable bidOffer = new JTable(){
          public boolean isCellEditable(int row, int column){
                    return false;
     JScrollPane bidOfferScroll = new JScrollPane(bidOffer);
     public MarketBook(String _mkbkID, Vector<String> _instList){
          super(_instList.firstElement());
          this.setDefaultCloseOperation(JFrame.HIDE_ON_CLOSE);
          this.mkbkID = _mkbkID;
          this.instrumentsList = _instList;
          this.instrument = instrumentsList.firstElement();
          buildGUI();
     private void buildGUI(){
          TableColumn tc = null;
          contentPane.setLayout(new BoxLayout(contentPane, BoxLayout.Y_AXIS));
          bidOfferScroll.setVerticalScrollBarPolicy(ScrollPaneConstants.VERTICAL_SCROLLBAR_AS_NEEDED);
          bidOfferScroll.setHorizontalScrollBarPolicy(ScrollPaneConstants.HORIZONTAL_SCROLLBAR_NEVER);
          bidOfferScroll.setPreferredSize(new Dimension(PREF_WIDTH,PREF_HEIGHT));
          System.err.println("Max: " + bidOfferScroll.getVerticalScrollBar().getMaximum());
          System.err.println("Min: " + bidOfferScroll.getVerticalScrollBar().getMinimum());
          System.err.println("Extent: " + bidOfferScroll.getVerticalScrollBar().getVisibleAmount());
          System.err.println("Value: " + bidOfferScroll.getVerticalScrollBar().getValue());
          bidOfferScroll.getVerticalScrollBar().setValueIsAdjusting(true);
          bidOfferScroll.getVerticalScrollBar().setValue(50);
          System.err.println("Value: " + bidOfferScroll.getVerticalScrollBar().getValue());
          System.err.println("Model: " + bidOfferScroll.getVerticalScrollBar().getModel());          
                    bidOfferScroll.getVerticalScrollBar().getMaximum()-
                    bidOfferScroll.getVerticalScrollBar().getMinimum())/2);*/
          topPanel.setLayout(new FlowLayout(FlowLayout.LEFT));
          topPanel.add(instList);
          instList.addActionListener(this);
          bidOffer.getTableHeader().setFont(new Font(null, Font.BOLD, 12));
          bidOffer.setAlignmentX(JTable.CENTER_ALIGNMENT);
          bidOffer.setModel(dm);
          bidOffer.getColumnModel().getColumn(0).setPreferredWidth(40);
          bidOffer.getColumnModel().getColumn(1).setPreferredWidth(60);
          bidOffer.getColumnModel().getColumn(2).setPreferredWidth(60);
          bidOffer.getColumnModel().getColumn(3).setPreferredWidth(40);               
          bidOffer.setRowHeight(ROW_HEIGHT);
          // Set table renderer
          for(int i = 0; i < bidOffer.getColumnCount(); i++){
               tc = bidOffer.getColumnModel().getColumn(i);
               tc.setCellRenderer(new CustomTableCellRenderer());
          contentPane.add(topPanel);
          contentPane.add(bidOfferScroll);
          JFrame.setDefaultLookAndFeelDecorated(true);
          this.setContentPane(contentPane);
          this.pack();
          this.setVisible(true);
     public void actionPerformed (ActionEvent e){
          JComboBox cb = (JComboBox)e.getSource();
          String selectedItem = (String)cb.getSelectedItem();
          updateSelectedInst(selectedItem);
     public void windowActivated(WindowEvent arg0) {
          // TODO Auto-generated method stub
     public void windowClosed(WindowEvent arg0) {
          // TODO Auto-generated method stub
     public void windowClosing(WindowEvent arg0) {
          // TODO Auto-generated method stub
          this.setVisible(false);
          this.dispose();
          System.exit(0);
     public void windowDeactivated(WindowEvent e) {
          // TODO Auto-generated method stub
     public void windowDeiconified(WindowEvent e) {
          // TODO Auto-generated method stub
     public void windowIconified(WindowEvent e) {
          // TODO Auto-generated method stub
     public void windowOpened(WindowEvent e) {
          // TODO Auto-generated method stub
     // Perform all updates necessary when new instrument is selected
     private void updateSelectedInst(String inst){
          this.setTitle(inst);
     class CustomTableCellRenderer extends DefaultTableCellRenderer{
          public Component getTableCellRendererComponent(JTable table,
                    Object value, boolean isSelected, boolean hasFocus,
                    int row, int column){
               Component cell = super.getTableCellRendererComponent(table,
                                   value, isSelected, hasFocus, row, column);
               if (column == BID_COL){
                    cell.setBackground(Color.red);
               else if (column == OFFER_COL){
                    cell.setBackground(Color.blue);
               //cell.setFont(f)
               return cell;
     public static void main(String args[]){
          Vector<String> tempVector = new Vector<String>();
          tempVector.add("item1");
          tempVector.add("item2");
          MarketBook marketBook1 = new MarketBook("mkbk1", tempVector);
}