的Java addMouseListener將接受甲骨文例如

奇怪的說法下面是使用從Oracle網站的MouseEvent的例子：的Java addMouseListener將接受甲骨文例如

我不希望任何人通過整個代碼讀取。我只是在下面的代碼的特定行感興趣：

addMouseListener(this); //WHY IS "this" ALLOWED AS AN ARGUMENT?

在這條線的甲骨文網站給出的代碼，他們正試圖添加的MouseListener的面板。這可以。但是，引用面板引用的this正被用作addMouseListener（）方法的參數。 爲什麼允許這樣做？

我檢查了addMouseListener API，它只允許一個MouseListener對象，爲什麼面板對象被允許在這裏？

addMouseListener將API：http://docs.oracle.com/javase/7/docs/api/java/awt/Component.html#addMouseListener(java.awt.event.MouseListener)

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

import javax.swing.*; 

public class MouseEventDemo extends JPanel 
     implements MouseListener { 
    BlankArea blankArea; 
    JTextArea textArea; 
    static final String NEWLINE = System.getProperty("line.separator"); 

    public static void main(String[] args) { 
     /* Use an appropriate Look and Feel */ 
     try { 
      //UIManager.setLookAndFeel("com.sun.java.swing.plaf.windows.WindowsLookAndFeel"); 
      //UIManager.setLookAndFeel("com.sun.java.swing.plaf.gtk.GTKLookAndFeel"); 
      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); 
     //Schedule a job for the event dispatch thread: 
     //creating and showing this application's GUI. 
     javax.swing.SwingUtilities.invokeLater(new Runnable() { 
      public void run() { 
       createAndShowGUI(); 
      } 
     }); 
    } 

    /** 
    * Create the GUI and show it. For thread safety, 
    * this method should be invoked from the 
    * event dispatch thread. 
    */ 
    private static void createAndShowGUI() { 
     //Create and set up the window. 
     JFrame frame = new JFrame("MouseEventDemo"); 
     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() { 
     super(new GridLayout(0,1)); 
     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);  //WHY IS "this" ALLOWED AS AN ARGUMENT? 
     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); 
    } 
}

來源

2015-02-11 user3437460

我花了40分鐘試圖弄清楚oracle如何以不兼容的數據類型作爲參數。沒有意識到他們實現了MouseListener。有時候我不能否認Oracle寫的非常雜亂的代碼。 '：（' – user3437460 2015-02-11 22:36:29

注意類聲明：

public class MouseEventDemo extends JPanel 
     implements MouseListener {

特別是，將你的注意力到implements條款。類別MouseEventDemo的實例是MouseListener s，因此它們是JPanel.addMouseListener()的有效參數。

來源

2015-02-11 22:32:43

您的類不延長只是一個JPanel。它還實現了MouseListener接口。因此，您可以將this作爲引用當前對象的參數。

來源

2015-02-11 22:32:13

我不敢相信我錯過了那條路。omg！ – user3437460 2015-02-11 22:32:55

因爲MouseEventDemo實現了MouseListener接口。因此MouseEventDemo的實例可以傳遞

來源

2015-02-11 22:32:19 Kode

的Java addMouseListener將接受甲骨文例如

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