title: Java - Changing JLabel Frontcolor in extern function
body: <p>As a beginner in Java i try to create a Window Application "Game" with the help of windowsbuilder (eclipse plugin).
  Now as i try to change The label in an extern function (allblack()) the console gives out the following errors when i press the specific button (The window gets displayed correctly):</p>
  
  <pre><code>Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
      at Leiterspiel.allblack(Leiterspiel.java:81)
      at Leiterspiel$2.mouseClicked(Leiterspiel.java:234)
      at java.awt.AWTEventMulticaster.mouseClicked(Unknown Source)
      at java.awt.Component.processMouseEvent(Unknown Source)
      at javax.swing.JComponent.processMouseEvent(Unknown Source)
      at java.awt.Component.processEvent(Unknown Source)
      at java.awt.Container.processEvent(Unknown Source)
      at java.awt.Component.dispatchEventImpl(Unknown Source)
      at java.awt.Container.dispatchEventImpl(Unknown Source)
      at java.awt.Component.dispatchEvent(Unknown Source)
      at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
      at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
      at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
      at java.awt.Container.dispatchEventImpl(Unknown Source)
      at java.awt.Window.dispatchEventImpl(Unknown Source)
      at java.awt.Component.dispatchEvent(Unknown Source)
      at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
      at java.awt.EventQueue.access$500(Unknown Source)
      at java.awt.EventQueue$3.run(Unknown Source)
      at java.awt.EventQueue$3.run(Unknown Source)
      at java.security.AccessController.doPrivileged(Native Method)
      at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
      at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
      at java.awt.EventQueue$4.run(Unknown Source)
      at java.awt.EventQueue$4.run(Unknown Source)
      at java.security.AccessController.doPrivileged(Native Method)
      at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
      at java.awt.EventQueue.dispatchEvent(Unknown Source)
      at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
      at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
      at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
      at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
      at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
      at java.awt.EventDispatchThread.run(Unknown Source)
  Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
      at Leiterspiel.allblack(Leiterspiel.java:81)
      at Leiterspiel$2.mouseClicked(Leiterspiel.java:234)
      at java.awt.AWTEventMulticaster.mouseClicked(Unknown Source)
      at java.awt.Component.processMouseEvent(Unknown Source)
      at javax.swing.JComponent.processMouseEvent(Unknown Source)
      at java.awt.Component.processEvent(Unknown Source)
      at java.awt.Container.processEvent(Unknown Source)
      at java.awt.Component.dispatchEventImpl(Unknown Source)
      at java.awt.Container.dispatchEventImpl(Unknown Source)
      at java.awt.Component.dispatchEvent(Unknown Source)
      at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
      at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
      at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
      at java.awt.Container.dispatchEventImpl(Unknown Source)
      at java.awt.Window.dispatchEventImpl(Unknown Source)
      at java.awt.Component.dispatchEvent(Unknown Source)
      at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
      at java.awt.EventQueue.access$500(Unknown Source)
      at java.awt.EventQueue$3.run(Unknown Source)
      at java.awt.EventQueue$3.run(Unknown Source)
      at java.security.AccessController.doPrivileged(Native Method)
      at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
      at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
      at java.awt.EventQueue$4.run(Unknown Source)
      at java.awt.EventQueue$4.run(Unknown Source)
      at java.security.AccessController.doPrivileged(Native Method)
      at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
      at java.awt.EventQueue.dispatchEvent(Unknown Source)
      at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
      at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
      at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
      at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
      at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
      at java.awt.EventDispatchThread.run(Unknown Source)
  </code></pre>
  
  <p>I'd be greatful if anyone could explain it to me as the same code as in  "allblack()" works in "inizialize()".
  Thanks</p>
  
  <pre><code>[Pre-sampled import]
  public void allblack()
   {
      l1.setForeground(Color.black);
      l2.setForeground(Color.black);
   }
   public void initialize() {
  
      frmDasLeiterspiel = new JFrame();
      frmDasLeiterspiel.setResizable(false);
      frmDasLeiterspiel.setTitle("Das Leiterspiel");
      frmDasLeiterspiel.setBounds(100, 100, 420, 420);
      frmDasLeiterspiel.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frmDasLeiterspiel.getContentPane().setLayout(null);
  
      JLabel l1 = new JLabel("1");
      l1.setBackground(Color.LIGHT_GRAY);
      l1.setBounds(340, 190, 50, 50);
      l1.setHorizontalAlignment(SwingConstants.CENTER);
      frmDasLeiterspiel.getContentPane().add(l1, BorderLayout.CENTER);
  
      JLabel l2 = new JLabel("2");
      l2.setBackground(Color.LIGHT_GRAY);
      l2.setHorizontalAlignment(SwingConstants.CENTER);
      l2.setBounds(278, 190, 50, 50);
      frmDasLeiterspiel.getContentPane().add(l2);
      [....]
      JButton btnNewButton = new JButton("Roll the dice!");
      btnNewButton.addMouseListener(new MouseAdapter() {
          @Override
          public void mouseClicked(MouseEvent arg0) {
              allblack();
          }
      });
      btnNewButton.setBounds(12, 294, 378, 25);
      frmDasLeiterspiel.getContentPane().add(btnNewButton);
      [...]
      }
  </code></pre>