20170204Exception in thread "main" java.lang.NullPointerException

Exception in thread "main" java.lang.NullPointerException
 at com.txw.Ftest.getControlPanel(Ftest.java:28)
 at com.txw.Ftest.getJContentPane(Ftest.java:93)
 at com.txw.Ftest.initialize(Ftest.java:85)
 at com.txw.Ftest.<init>(Ftest.java:81)
 at com.txw.Ftest.main(Ftest.java:99)

public class Ftest extends JFrame {private JScrollPane scrollPane;private static final long serialVersionUID=1L;private JPanel jContentPane=null;private JTextArea jTextArea=null;private JPanel controlPanel=null;private JButton openButton=null;private JButton closeButton=null;private JTextArea getJTextArea(){if(jTextArea==null){jTextArea=new JTextArea();}return jTextArea;}private JPanel getControlPanel(){if(controlPanel==null){FlowLayout flowLayout=new FlowLayout();flowLayout.setVgap(1);controlPanel=new JPanel(); //缺少此行就会报错controlPanel.setLayout(flowLayout);controlPanel.add(getOpenButton(), null);controlPanel.add(getCloseButton(),null);}return controlPanel;}private JButton getOpenButton(){if(openButton==null){openButton=new JButton();openButton.setText("写入文件");openButton//.addActionListener(new java.awt.event.ActionListerner(){//java.awt.event.ActionListerner cannot be resolved to a type, "ActionListerner"字母写错，改为“ActionListener”.addActionListener(new java.awt.event.ActionListener(){public void actionPerformed(ActionEvent e){File file=new File("word.txt");try{FileWriter out=new FileWriter(file);String s=jTextArea.getText();out.write(s);out.close();}catch(Exception e1){e1.printStackTrace();}}});}return openButton;}private JButton getCloseButton(){if(closeButton==null){closeButton=new JButton();closeButton.setText("读取文件");closeButton.addActionListener(new java.awt.event.ActionListener(){public void actionPerformed(ActionEvent e){File file=new File("word.txt");try{FileReader in=new FileReader(file);char byt[]=new char[1024];int len=in.read(byt);jTextArea.setText(new String(byt,0,len));in.close();}catch(Exception e1){e1.printStackTrace();}}});}return closeButton;}public Ftest(){super();initialize();}    private void initialize(){    this.setSize(300,200);    this.setContentPane(getJContentPane());    this.setTitle("JFrame");    }    private JPanel getJContentPane(){    if(jContentPane==null){    jContentPane=new JPanel();    jContentPane.setLayout(new BorderLayout());    jContentPane.add(getScrollPane(), BorderLayout.CENTER);    jContentPane.add(getControlPanel(),BorderLayout.SOUTH);    }    return jContentPane;    }public static void main(String[] args) {// TODO Auto-generated method stub    Ftest thisClass=new Ftest();    thisClass.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);    thisClass.setVisible(true);}protected JScrollPane getScrollPane(){if(scrollPane==null){scrollPane=new JScrollPane();scrollPane.setViewportView(getJTextArea());}return scrollPane;}}

                                             
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