JPanels沒有通過其他顯示如果語句

我試圖讓一個基本的看起來與左邊的按鈕，然後他們鏈接到的面板應該彈出，但即時通訊有一些問題，讓它正常工作JPanels沒有通過其他顯示如果語句

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

public class MtnDew extends JApplet implements ActionListener 
{ 
    JButton home, first, faq, contact; 
    Image img; 
JLabel title, logo, copyright, ntbkImg, firstMsg, ntbkDesc, infoSheets, welcomeMsg; 
JLabel basket; 
Color blackColor = new Color(10, 10, 10); 
Color greenColor = new Color(10,200,50); 
JPanel leftside, top, center, welcome, firstPanel,contactPanel, separator;                       
Jpanel faqPanel; 
public void init() 
{ 
    setLayout(new BorderLayout()); 
    doTitle(); 
    doLeftSide(); 
    doBottom(); 
    doCenter(); 
    setupFAQPanel(); 
} 
public void setupButton(JButton b) 
{ 
    b.setContentAreaFilled(false); 
    b.setBorderPainted (false); 
    b.setFocusable(false); 
    b.setForeground (blackColor); 
    b.addActionListener (this); 
    leftside.add(b); 
} 
public void doTitle() 
{ 
    title = new JLabel("<HTML>The DewMocracy",JLabel.CENTER); 
    img = getImage(getCodeBase(), "MtnDew1.jpeg"); 
    logo = new JLabel (new ImageIcon(img)); 
    img = getImage(getCodeBase(), "MtnDew2.jpeg"); 
    title = new JLabel (new ImageIcon(img)); 
    top = new JPanel (new FlowLayout()); 
    top.add(logo); 
    top.add(title); 
    top.setBackground (blackColor); 
    add(top, BorderLayout.NORTH); 
} 
public void doLeftSide() 
{ 
    //Links on left bar 
    leftside = new JPanel (new GridLayout(5, 1)); 
    leftside.setBackground(greenColor); 
    home = new JButton ("Home"); 
    first = new JButton ("First DewMocracy"); 
    faq = new JButton ("FAQ"); 
    contact = new JButton ("Contact Us"); 
    setupButton (home); 
    setupButton (first); 
    setupButton (faq); 
    setupButton (contact); 
    basket = new JLabel(new ImageIcon(getImage( getCodeBase(),"MtnDew3.jpeg"))); 
    leftside.add(basket); 
    add(leftside, BorderLayout.WEST); 
} 
public void doBottom() 
{ 
    copyright = new JLabel("<HTML>Text from dobottom",JLabel.CENTER); 
    copyright.setForeground(blackColor); 
    copyright.setOpaque(true); 
    copyright.setBackground(greenColor); 
    add(copyright, BorderLayout.SOUTH); 
} 

public void doCenter() 
{ 
    center = new JPanel (new BorderLayout()); 
    center.setBackground(blackColor); 
    separator = new JPanel(); 
    separator.setBackground (greenColor); 
    separator.setPreferredSize(new Dimension (10, 20)); 
    center.add(separator, BorderLayout.NORTH); 

    welcome = new JPanel(new FlowLayout()); 
    welcome.setOpaque(false); 
    welcomeMsg = new JLabel("<html><center>" 
      + "<H2>this is a welcome message</H2>"); 
    welcomeMsg.setForeground(greenColor); 
    welcome.add(welcomeMsg); 
    center.add(welcome,BorderLayout.CENTER); 
    add(center, BorderLayout.CENTER); 
} 
public void setupcontactPanel() 
{ 
    JLabel contactText = new JLabel ("<HTML><H1>FAQ</H1>" 
      + "contact panel test"); 
    contactPanel = new JPanel (new FlowLayout()); 
    contactPanel.setOpaque(false); 
    contactPanel.add(contactText); 
} 
public void setupFAQPanel() 
{ 
    JLabel faqText = new JLabel ("<HTML><H1>FAQ</H1>" 
      + "lots bla text can go here"); 
    faqPanel = new JPanel (new FlowLayout()); 
    faqPanel.setOpaque(false); 
    faqPanel.add(faqText); 
} 
public void actionPerformed (ActionEvent ae) 
{ 
    JButton src = (JButton)ae.getSource(); 
    center.removeAll(); 
    separator = new JPanel(); 
    separator.setBackground (greenColor); 
    separator.setPreferredSize(new Dimension (10, 20)); 
    center.add(separator, BorderLayout.NORTH); 
    if (src.equals(home)) 
    { 
     center.removeAll(); 
     center.add(welcome,BorderLayout.CENTER); 
    } 
    else if (src.equals(contact)) 
    { 
     center.removeAll(); 
     center.add(contactPanel, BorderLayout.CENTER); 
    } 
    else if (src.equals(faq)) 
    { 
     center.removeAll(); 
     center.add(faqPanel, BorderLayout.CENTER); 
    } 
    else if (src.equals(first)) 
    { 
     center.removeAll(); 
     center.add(firstPanel, BorderLayout.CENTER); 
    } 
    center.repaint(); 
    validate(); 
    repaint(); 
    } 

}

我一直試圖讓它工作，我甚至開始做一個簡單的版本，但它也不工作。這似乎是什麼與我的如果陳述，或即時通訊不瞭解的行動事件的關鍵要素

編輯：我改變了現在在代碼中的If語句，它仍然無法正常工作。我可以點擊家庭和常見問題，但我的其他兩個jbuttons似乎不工作。即時通訊試圖使用接觸按鈕

來源

2013-11-21 user3019370

我會大膽地猜測，並說這是因爲你不使用」 .equals'來評價您的謂詞。 '=='只檢查內存位置。 – Max

Contact Us和First DewMocracy按鈕不作爲NullPointerException的結果工作。 contactPanel和firstPanel從未初始化，當您嘗試將它們添加到面板actionPerformed()時，它們是null。

另外，請看A Visual Guide to Layout Managers。 CardLayout可能會有所幫助，而不是手動更換面板。

來源

2013-11-21 22:27:08 tenorsax

變化

Object src = ae.getSource();

到

Jbutton src = (JButton)ae.getSource();

然後

if(src.equals(home))

或

if(src.equals(contact))

，以測試它

等等......

來源

2013-11-21 21:30:40

您應該將它們添加到代碼頂部的容器中，初始化它們時，然後在其他if語句使用時將它們添加到容器中;

contactPanel.setVisible(true);

等，爲所有的人

來源

2013-11-21 22:28:19

JPanels沒有通過其他顯示如果語句

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