DataInputStream的问题，帮帮忙哈1

void jButtonSend_actionPerformed(ActionEvent e) {
    msgStr2=jTextArea_msg.getText();
    try {
      dout = new DataOutputStream(s.getOutputStream());///这儿报错了
      dout.writeUTF(msgStr2);
      dout.close();
    }
    catch (IOException ex) {
    }
}
dout 在这个类的最前面已经申明了的：
DataOutputStream dout;
还有s为Socket型，msgStr2为String型！
其中
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错误报告：
java.lang.NullPointerException at sslchat.Frame1.jButtonSend_actionPerformed(Frame1.java:177) at sslchat.Frame1_jButtonSend_actionAdapter.actionPerformed(Frame1.java:243) at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1786) at javax.swing.AbstractButton$ForwardActionEvents.actionPerformed(AbstractButton.java:1839) at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:420) at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:258) at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:245) at java.awt.Component.processMouseEvent(Component.java:5100) at java.awt.Component.processEvent(Component.java:4897) at java.awt.Container.processEvent(Container.java:1569) at java.awt.Component.dispatchEventImpl(Component.java:3615) at java.awt.Container.dispatchEventImpl(Container.java:1627) at java.awt.Component.dispatchEvent(Component.java:3477) at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:3483) at java.awt.LightweightDispatcher.processMouseEvent(Container.java:3198) at java.awt.LightweightDispatcher.dispatchEvent(Container.java:3128) at java.awt.Container.dispatchEventImpl(Container.java:1613) at java.awt.Window.dispatchEventImpl(Window.java:1606) at java.awt.Component.dispatchEvent(Component.java:3477) at java.awt.EventQueue.dispatchEvent(EventQueue.java:456) at java.awt.EventDispatchThread.pumpOneEventForHierarchy(EventDispatchThread.java:201) at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:151) at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:145) at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:137) at java.awt.EventDispatchThread.run(EventDispatchThread.java:100)