Eu escrevi umMouseListener conforme definido abaixo, para que eu possa mover umJButton para reordenar os componentes que estão dentro doJPanel. oJPanel está dentro de umJScrollPane para que, quando vários componentes forem adicionados, eles possam ser rolados.

O problema que tenho é que, ao arrastar o componente e o mouse sair da janela de rolagem / janela de exibição, o componente retornará à sua posição dentro doJPanel então será desenhado no local correto. Suponho que esse comportamento seja devido ao fato de a Viewport chamar uma repintura de seus filhos quando eu ligoscrollRectToVisible()

Existe uma maneira de impedir que isso aconteça?

Observe que estou limitado ao Java 5

Ouvinte

import java.awt.Component;
import java.awt.Container;
import java.awt.MouseInfo;
import java.awt.Point;
import java.awt.Rectangle;
import java.awt.event.MouseEvent;
import javax.swing.JViewport;
import javax.swing.SwingUtilities;
import javax.swing.event.MouseInputAdapter;

public class DragListener extends MouseInputAdapter
{
    private Point location;
    private MouseEvent pressed;
    private MouseEvent dragged;
    private MouseEvent dropped;

    @Override
    public void mousePressed(MouseEvent me)
    {
        pressed = me;
    }

    @Override
    public void mouseDragged(MouseEvent me)
    {
        dragged = me;
        Component component = dragged.getComponent();
        Container parent = component.getParent();
        Container superParent = parent.getParent();

        if(superParent instanceof JViewport)
        {
            JViewport vp = (JViewport)superParent;
            Rectangle vpb = vp.getBounds();
            Point pt = MouseInfo.getPointerInfo().getLocation();
            SwingUtilities.convertPointFromScreen(pt, vp);

            if(!vpb.contains(pt))
            {
                int yDiff = (pt.y < vpb.y ) ? pt.y : pt.y - vpb.height;
                vpb.translate(0, yDiff);
                vp.scrollRectToVisible(vpb);
            }
        }

        location = component.getLocation(location);
        int x = location.x - pressed.getX() + me.getX();
        int y = location.y - pressed.getY() + me.getY();
        component.setLocation(x, y);
    }

    // Mouse release omitted
}

Gui (Criado no NetBeans)

import java.awt.Rectangle;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionAdapter;
import java.awt.event.MouseMotionListener;
import javax.swing.JButton;
import javax.swing.JPanel;

public class DragginTest extends javax.swing.JFrame
{
    public DragginTest()
    {
        initComponents();
        addListeners(jButton1, jButton2, jButton3, jButton4, jButton5, jButton6, jButton7, jButton8, jButton9);
    }

    private void addListeners(JButton... buttons)
    {
        DragListener drag = new DragListener();
        for(JButton b : buttons)
        {
            b.addMouseListener(drag);
            b.addMouseMotionListener(drag); 
        }   
    }

    @SuppressWarnings("unchecked")

    private void initComponents()
    {
        jLayeredPane1 = new javax.swing.JLayeredPane();
        jScrollPane1 = new javax.swing.JScrollPane();
        mainPanel = new javax.swing.JPanel();
        jButton1 = new javax.swing.JButton();
        jButton2 = new javax.swing.JButton();
        jButton3 = new javax.swing.JButton();
        jButton4 = new javax.swing.JButton();
        jButton5 = new javax.swing.JButton();
        jButton6 = new javax.swing.JButton();
        jButton7 = new javax.swing.JButton();
        jButton8 = new javax.swing.JButton();
        jButton9 = new javax.swing.JButton();

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
        setPreferredSize(new java.awt.Dimension(450, 450));

        mainPanel.setLayout(new java.awt.GridLayout(5, 2, 2, 2));

        // Below Repeated for buttons 1-9 (left out for conciseness)
        jButton1.setFont(new java.awt.Font("Tahoma", 1, 48)); // NOI18N
        jButton1.setForeground(new java.awt.Color(255, 0, 0));
        jButton1.setText("1");
        mainPanel.add(jButton1);
        // End Repeat

        jScrollPane1.setViewportView(mainPanel);

        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGroup(javax.swing.GroupLayout.Alignment.TRAILING, layout.createSequentialGroup()
            .addGap(40, 40, 40)
            .addComponent(jScrollPane1, javax.swing.GroupLayout.PREFERRED_SIZE, 205, javax.swing.GroupLayout.PREFERRED_SIZE)
            .addGap(38, 38, 38))
        );
        layout.setVerticalGroup(
        layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGroup(layout.createSequentialGroup()
            .addGap(40, 40, 40)
            .addComponent(jScrollPane1, javax.swing.GroupLayout.PREFERRED_SIZE, 226, javax.swing.GroupLayout.PREFERRED_SIZE)
            .addContainerGap(53, Short.MAX_VALUE))
        );

        pack();
    }

    public static void main(String args[])
    {
        /* Create and display the form */
        java.awt.EventQueue.invokeLater(new Runnable()
        {
            public void run()
            {
                new DragginTest().setVisible(true);
            }
        });
    }

    private javax.swing.JButton jButton1;
    private javax.swing.JButton jButton2;
    private javax.swing.JButton jButton3;
    private javax.swing.JButton jButton4;
    private javax.swing.JButton jButton5;
    private javax.swing.JButton jButton6;
    private javax.swing.JButton jButton7;
    private javax.swing.JButton jButton8;
    private javax.swing.JButton jButton9;
    private javax.swing.JLayeredPane jLayeredPane1;
    private javax.swing.JScrollPane jScrollPane1;
    private javax.swing.JPanel mainPanel;
}