JSlider问题

Question

我正在创建一个程序，使用滚动条选择标签的前景色，三个水平滚动条用于选择颜色的红色绿色和蓝色分量。我需要一个包含滚动条的面板上的标题边框。我只是开始了。我遇到了这个messagePanel的问题。

import java.awt.*;
import javax.swing.*;

public class MessagePanel extends JPanel
{
    //The message to be displayed
    private String message;
    //The x-Coordinate
    private int xCoordinate;
    //The y-Coordinate
    private int yCoordinate;
    //Centered
    private boolean centered;
    //Interval length for moving message horizontally and vertically
    private int interval = 10;

    public MessagePanel()
    {
    }

    //Construct message panel with a specific message
    public MessagePanel(String message)
    {
        this.message = message;
    }

    //Return that specific message
    public String getMessage()
    {
        return message;
    }

    //Set a new message
    public void setMessage(String message)
    {
        this.message = message;
        repaint();
    }

    //Return xCoordinate
    public int getXCoordinate()
    {
        return xCoordinate;
    }

    //Set a new xCoordinate
    public void setXCoordinate(int x)
    {
        this.xCoordinate = x;
        repaint();
    }

    //Return yCoordinate
    public int getYCoordinate()
    {
        return yCoordinate;
    }

    //Set a new yCoordinate
    public void setYCoordinate(int y)
    {
        this.yCoordinate = y;
        repaint();
    }

    //Return Centered
    public boolean isCentered()
    {
        return centered;
    }

    //Set a new Centered
    public void setCenetered(boolean centered)
    {
        this.centered = centered;
    }

    //Return interval
    public int getInterval()
    {
        return interval;
    }

    //Set a new interval
    public void setInterval(int interval)
    {
        this.interval = interval;
        repaint();
    }

    //Paint the Message
    protected void paintComponent(Graphics g)
    {
        super.paintComponent(g);

        if (centered)
        {
            //Current metrics for current font
            FontMetrics fm = g.getFontMetrics();

            //Find the center location to display                                               
            int stringWidth = fm.stringWidth(message);
            int stringAscent = fm.getAscent();

            //Get the position of the leftmost char in the baseline
            int xCoordinate = getWidth() / 2 - stringWidth / 2;
            int yCoordinate = getHeight() / 2 + stringAscent / 2;
        }

        //Draw String   
        g.drawString(message, xCoordinate, yCoordinate);
    }

    //Move the message to the left
    public void moveLeft()
    {
        xCoordinate -= interval;
        repaint();
    }

    //Move the message to the right
    public void moveRight()
    {
        xCoordinate += interval;
        repaint();
    }

    //Move the message up
    public void moveUp()
    {
        yCoordinate -= interval;
        repaint();
    }

    //Move the message down
    public void moveDown()
    {
        yCoordinate += interval;
        repaint();
    }

    //Override get method for preferredSize
    public Dimension getPreferredSize()
    {
        return new Dimension(200, 30);
    }
}

这可能是ScrollBar类：

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.border.TitledBorder;

public class ScrollBar extends JFrame
{
    //Creating scroll bars
    private JSlider jslHorz1 = new JSlider(JSlider.HORIZONTAL);
    private JSlider jslHorz2 = new JSlider(JSlider.HORIZONTAL);
    private JSlider jslHorz3 = new JSlider(JSlider.HORIZONTAL);

    //Creating the message panel
    private MessagePanel messagePanel = new MessagePanel("Show Color");

    //Adding scroll bars and message panel
    public ScrollBar(){
        //Creating UI
        setLayout(new BorderLayout(3, 3));

        //Adding messagePanel
        add(messagePanel, BorderLayout.CENTER);

        //Adding the scroll bars
        JPanel three = new JPanel(new GridLayout(3,1));
        three.add(new JLabel("Red"));
        three.add(jslHorz1);
        three.add(new JLabel("Green"));
        three.add(jslHorz2);
        three.add(new JLabel("Blue"));
        three.add(jslHorz3);
        add(three, BorderLayout.SOUTH);
        three.setBorder(new TitledBorder("Choose Color"));



    }

    //Main method
    public static void main(String[] args)
    {
        ScrollBar frame = new ScrollBar();
        frame.setTitle("Exercise 17_15");
        frame.setSize(300, 400);
        frame.setLocationRelativeTo(null);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    //  frame.pack();
        frame.setVisible(true);
    }
}