ScrollBar在Swing中的JScrollpane中移动不流畅

看一下JScrollBar.setUnitIncrement，因为与

JPanels

JScollPane

JList

JTable

Jtextarea

例

import javax.swing.*;import java.awt.*;import java.awt.event.*;public class JScrollBarUnitIncrement {    public static void main(String[] args) {        final Jframe f = new Jframe("");        JPanel panel = new JPanel();        panel.setLayout(new GridLayout(2000, 1));        for (int i = 0; i != 2000; i++) { JButton btn = new JButton("Button 2"); panel.add(btn);        }        final JScrollPane sPane = new JScrollPane(panel);        final int increment = 50;        sPane.getVerticalScrollBar().setUnitIncrement(increment);        KeyStroke kUp = KeyStroke.getKeyStroke(KeyEvent.VK_UP, 0);        KeyStroke kDown = KeyStroke.getKeyStroke(KeyEvent.VK_DOWN, 0);        sPane.getInputMap(JComponent.WHEN_ANCESTOR_OF_FOCUSED_COMPONENT).put(kUp, "actionWhenKeyUp");        sPane.getActionMap().put("actionWhenKeyUp", new AbstractAction("keyUpAction") { private static final long serialVersionUID = 1L; public void actionPerformed(ActionEvent e) {     final JScrollBar bar = sPane.getVerticalScrollBar();     int currentValue = bar.getValue();     bar.setValue(currentValue - increment); }        });        sPane.getInputMap(JComponent.WHEN_ANCESTOR_OF_FOCUSED_COMPONENT).put(kDown, "actionWhenKeyDown");        sPane.getActionMap().put("actionWhenKeyDown", new AbstractAction("keyDownAction") { private static final long serialVersionUID = 1L; public void actionPerformed(ActionEvent e) {     final JScrollBar bar = sPane.getVerticalScrollBar();     int currentValue = bar.getValue();     bar.setValue(currentValue + increment); }        });        f.setDefaultCloseOperation(Jframe.EXIT_ON_CLOSE);        f.add(sPane);        f.pack();        SwingUtilities.invokeLater(new Runnable() { public void run() {     f.setVisible(true); }        });    }    private JScrollBarUnitIncrement() {    }}