title: Java Swing: move JButton on click
body: <p>I'm in the process of learning to use swing components starting with the buttons. I'm trying to get a few buttons to move after clicking one of them. To set the initial location of the buttons, I have such code in my main class' constructor:</p>
  
  <pre><code>    setLayout(null);
      b1 = new JButton("Host");
      b1.setActionCommand("openServer");
      b1.addActionListener(this);
      b1.setBounds(300,10,200,30);
      add(b1);
  </code></pre>
  
  <p>And two more buttons. In the main method I</p>
  
  <pre><code>frame.setContentPane(newContentPane);
  </code></pre>
  
  <p>where the NewContentPane was set to be a new object of the main class. Which all works fine and beatifully. But then I click the button, the actionlistener starts its work. In its fine quest it again uses</p>
  
  <pre><code>b1.setBounds(-1,-1,0,0);
  b3.setBounds(30,30,50,30);
  </code></pre>
  
  <p>Or whatever, to hide b1 and make b3 appear which was hidden previously. This alone does nothing, as I expected. So I tried repainting the frame or the panel, which did nothing. So I thought, why not try the same old: setContentPane. And it works, the buttons move properly. But I get a bunch of errors as follows:</p>
  
  <pre><code>Exception in thread "AWT-EventQueue-0" java.awt.IllegalComponentStateException: contentPane cannot be set to null.
  at javax.swing.JRootPane.setContentPane(JRootPane.java:620)
  at javax.swing.JFrame.setContentPane(JFrame.java:693)
  at packtion.ButtStallion.actionPerformed(ButtStallion.java:86)
  at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2018)
  at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2341)
  at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
  at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
  at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252)
  at java.awt.Component.processMouseEvent(Component.java:6505)
  at javax.swing.JComponent.processMouseEvent(JComponent.java:3321)
  at java.awt.Component.processEvent(Component.java:6270)
  at java.awt.Container.processEvent(Container.java:2229)
  at java.awt.Component.dispatchEventImpl(Component.java:4861)
  at java.awt.Container.dispatchEventImpl(Container.java:2287)
  at java.awt.Component.dispatchEvent(Component.java:4687)
  at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4832)
  at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4492)
  at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4422)
  at java.awt.Container.dispatchEventImpl(Container.java:2273)
  at java.awt.Window.dispatchEventImpl(Window.java:2719)
  at java.awt.Component.dispatchEvent(Component.java:4687)
  at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:723)
  at java.awt.EventQueue.access$200(EventQueue.java:103)
  at java.awt.EventQueue$3.run(EventQueue.java:682)
  at java.awt.EventQueue$3.run(EventQueue.java:680)
  at java.security.AccessController.doPrivileged(Native Method)
  at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
  at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:87)
  at java.awt.EventQueue$4.run(EventQueue.java:696)
  at java.awt.EventQueue$4.run(EventQueue.java:694)
  at java.security.AccessController.doPrivileged(Native Method)
  at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
  at java.awt.EventQueue.dispatchEvent(EventQueue.java:693)
  at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:242)
  at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:161)
  at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:150)
  at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:146)
  at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:138)
  at java.awt.EventDispatchThread.run(EventDispatchThread.java:91)
  </code></pre>
  
  <p>I tried everything I could think of including googling. Google just gives links to how to set the initial location of buttons, could never find anything on how to change its location while the program is running.</p>
  
  <p>Thanks in advance.</p>