如何避免两个构造函数调用？

Question

我试图学习在Eclipse中开发插件，并在遵循Eclipse提供的教程之后，尝试通过编写一个简短的Java类来跟踪和显示文本区域上的鼠标移动来扩展代码。我从Oracle Java文档中获得了相应的代码。以下是我称之为鼠标跟踪类（MouseEventDemo）的java类：

package com.example.helloworld.handlers;

import org.eclipse.core.commands.AbstractHandler;
import org.eclipse.core.commands.ExecutionEvent;
import org.eclipse.core.commands.ExecutionException;
import org.eclipse.ui.IWorkbenchWindow;
import org.eclipse.ui.handlers.HandlerUtil;
import org.eclipse.jface.dialogs.MessageDialog;

/**
 * Our sample handler extends AbstractHandler, an IHandler base class.
 * @see org.eclipse.core.commands.IHandler
 * @see org.eclipse.core.commands.AbstractHandler
 */
public class SampleHandler extends AbstractHandler {
    /**
     * The constructor.
     */
    public SampleHandler() {
    }

    /**
     * the command has been executed, so extract the needed information
     * from the application context.
     */
    public Object execute(ExecutionEvent event) throws ExecutionException {
        IWorkbenchWindow window = HandlerUtil.getActiveWorkbenchWindowChecked(event);
        MouseEventDemo md = new MouseEventDemo();
        md.callStart();

        return null;
    }
}

接下来，在MouseEventDemo类中， callStart（）通过调用 createAndShowGUI（）启动GUI绘制，然后调用 MouseEventDemo 类构造函数并完成工作。

package com.example.helloworld.handlers;

import javax.swing.*;


import java.awt.GridLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.event.MouseListener;
import java.awt.event.MouseEvent;

public class MouseEventDemo extends JPanel implements MouseListener {
    BlankArea blankArea;
    JTextArea textArea;
    static final String NEWLINE = System.getProperty("line.separator");
    String  wString;
    public void callStart(){
         try {
             UIManager.setLookAndFeel("javax.swing.plaf.metal.MetalLookAndFeel");
         } catch (UnsupportedLookAndFeelException ex) {
             ex.printStackTrace();
         } catch (IllegalAccessException ex) {
             ex.printStackTrace();
         } catch (InstantiationException ex) {
             ex.printStackTrace();
         } catch (ClassNotFoundException ex) {
             ex.printStackTrace();
         }
         /* Turn off metal's use of bold fonts */
         UIManager.put("swing.boldMetal", Boolean.FALSE);
         createAndShowGUI();
         //Schedule a job for the event dispatch thread:
         //creating and showing this application's GUI.
         //creating threaded implementation
         /*javax.swing.SwingUtilities.invokeLater(new Runnable() {
             public void run() {
                 createAndShowGUI();
             }
         });*/
    }

    public MouseEventDemo(String xx){
        super(new GridLayout(0,1));
        wString = xx;
        JOptionPane.showMessageDialog (null, "assigned");
    }

    private static void createAndShowGUI() {
        //Create and set up the window.
        JFrame frame = new JFrame("MouseDemo");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        //Create and set up the content pane.
        JComponent newContentPane = new MouseEventDemo();
        newContentPane.setOpaque(true); //content panes must be opaque
        frame.setContentPane(newContentPane);

        //Display the window.
        frame.pack();
        frame.setVisible(true);
    }

    public MouseEventDemo(){
        JOptionPane.showMessageDialog (null, wString);
        blankArea = new BlankArea(Color.YELLOW);
        add(blankArea);
        textArea = new JTextArea();
        textArea.setEditable(false);
        JScrollPane scrollPane = new JScrollPane(textArea);
        scrollPane.setVerticalScrollBarPolicy(
                JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);
        scrollPane.setPreferredSize(new Dimension(200, 75));
        add(scrollPane);

        //Register for mouse events on blankArea and the panel.
        blankArea.addMouseListener(this);
        addMouseListener(this);
        setPreferredSize(new Dimension(450, 450));
        setBorder(BorderFactory.createEmptyBorder(20,20,20,20));    
    }


    void eventOutput(String eventDescription, MouseEvent e) {
        textArea.append(eventDescription + " detected on "
                + e.getComponent().getClass().getName()
                + "." + NEWLINE);
        textArea.setCaretPosition(textArea.getDocument().getLength());      
    }

    public void mousePressed(MouseEvent e) {
        eventOutput("Mouse pressed (# of clicks: "
                + e.getClickCount() + ")", e);
    }

    public void mouseReleased(MouseEvent e) {
        eventOutput("Mouse released (# of clicks: "
                + e.getClickCount() + ")", e);
    }

    public void mouseEntered(MouseEvent e) {
        eventOutput("Mouse entered", e);
    }

    public void mouseExited(MouseEvent e) {
        eventOutput("Mouse exited", e);
    }

    public void mouseClicked(MouseEvent e) {
        eventOutput("Mouse clicked (# of clicks: "
                + e.getClickCount() + ")", e);
    }
}

在所有这些中，有两个MouseEventDemo对象实例被创建。首先从 SampleHandler 调用 callStart（），然后再在createAndShowGUI方法中的MouseEventDemo类中调用。第一个在初始调用之后根本没有使用，似乎完全浪费和资源的低效使用（只是在MouseEventDemo中调用一个公共方法）。

有没有更好的方法来完成预定的任务？