Question

您好我想将图表打印到applet窗口中，但在重新调整窗口大小之前图表是不可见的。

这是我的问题：我的代码有什么问题，我该如何解决这个问题？另外，我收到了以下行上的空指针异常

loop:for(int i=0; i <count.length; i++){

这是我的变量的问题，但我无法在此阶段修复它。我是一个初学者。

  public class Simple extends Applet implements ActionListener, KeyListener {

    Button analyze, reset, load;
    TextArea input, output;
    Panel panel, drawArea;
    JFileChooser fc;
    FileReader readFile;
    BufferedReader bufferedFile;
    String line = "";
    int count[];
    int length;
    int i ;
    int x  = 550;
    int y  = 320; 

      public void init() {
          setSize(800,600);
          setLayout (new BorderLayout());
          panel = new Panel(new GridLayout(0,3));
          panel.add(analyze = new Button("Analyze"));
          panel.add(load = new Button("Load"));
          panel.add(reset = new Button("Reset"));
          add(panel,BorderLayout.SOUTH);

          panel = new Panel(new GridLayout(2,1));
          panel.setPreferredSize(new Dimension(200,0));
          panel.add(input = new TextArea());
          panel.add(output = new TextArea());
          add(panel,BorderLayout.WEST);
      /*
          panel.add(drawArea = new Panel());
          add(drawArea,BorderLayout.CENTER);
          drawArea.getGraphics();
       */         
          analyze.addActionListener(this);
          analyze.setEnabled(false);
          load.addActionListener(this);
          reset.addActionListener(this);

          input.addKeyListener(this);
          output.setEditable(false);    

          fc = new JFileChooser();  

          setBackground(Color.cyan);

      }
      public void start() {
            System.out.println("starting...");
      }
      public void stop() {
            System.out.println("stopping...");
      }
      public void destroy() {
            System.out.println("preparing to unload...");
      }

        @Override
        public void keyPressed(KeyEvent e) {
            String inputGetText = input.getText();
            if (inputGetText != null) {
                analyze.setEnabled(true);                    
                } 
        }
        @Override
        public void keyReleased(KeyEvent e) {

        }
        @Override
        public void keyTyped(KeyEvent e) {

        }

    public void actionPerformed(ActionEvent event){
        if (event.getSource()==analyze) {
            input.setEditable(false);   
            analyze.setEnabled(false);
            wordProcess();
        }

        if (event.getSource()==load){
            fc.showOpenDialog(load);        

            File file = fc.getSelectedFile();

            try {
                readFile = new FileReader(file);
            } catch (FileNotFoundException e) {
                e.printStackTrace();
            }

            BufferedReader bufferedFile = new BufferedReader(readFile);

            try {
                String nLine = bufferedFile.readLine();
                while (nLine!=null){
                    line+=nLine + "\n";
                     nLine = bufferedFile.readLine();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }   

            input.setText(line);
            analyze.setEnabled(true);                       
        }

        if (event.getSource()==reset){
            input.setText(null);
            input.setEditable(true);    
            output.setText(null);
            //x = 50;
            line = "";
            analyze.setEnabled(false);                    
        }
    }

    public void wordProcess(){

        for(String retva1: input.getText().replaceAll("[^a-zA-Z]+"," ").split(" "))
                if(length < retva1.length())
                    length = retva1.length();

             count = new int [length+1];

        for(String retva2: input.getText().replaceAll("[^a-zA-Z]+"," ").split(" ")){
            count[retva2.length()]++;
            }
            String show = "";
            float average = 0;
            float sum = 0;
            float sum2 = 0;
            loop:   for(int i = 0; i <count.length; i++){
                if (count[i]==0||i==0){
                    continue loop;          
                }else{
                    show += (count[i]+" words of length "+i) + "\n";
                    sum2 +=i*count[i];
                    average +=count[i];                     
                }
                output.setText("There are: "+"\n"+show);
            }
            sum = sum2/average;
            String s2 = new Float(sum2).toString();
            String a = new Float(average).toString();

            output.append("\n"+"The mean word length: "+sum);
            output.append("\n"+s2);
            output.append("\n"+a);              
    }

    public void paint(Graphics g) {

            g.drawLine(250, 50, 250, 320);
            g.drawLine(250, 320, 520, 320); 

            g.drawLine(250, 340, 250, 610 );
            g.drawLine(250, 610, 520, 610);   

        loop:   for(int i=0; i <count.length; i++){
            if (count[i]==0||i==0){
                continue loop;          
            }else{

                int wordFreqency = count[i];
                int wordLenght = i;
                g.fillRect( x , y-(wordFreqency*5), 10, wordFreqency*5);          
                String scaleIndexX = new Integer(i).toString();
                g.drawString(scaleIndexX, x, 335);
                String scaleIndexY = new Integer(count[i]).toString();
                g.drawString(scaleIndexY, x, y-(wordFreqency*5+5));
            System.out.println(x);
            int move = 0;
            if (move<wordLenght){
                x+=20; 
                    }
                }
            } 
    }
}

Answer 1

count数组变量最初为null，仅当actionPerformed方法调用wordProcess()时才在按钮上创建。所以你的绘图例程试图使用null变量。解决方案：在尝试使用if进行绘制之前，使用if控件检查count是否为null。

if (count != null) {
  // can use count here
}

顺便说一句：你使用Swing而不是AWT会好得多。

此外，在获得绘制图表所需的所有信息后，请在actionPerformed方法中调用repaint()。

重新调整applet窗口大小时出现的Java图表

1 个答案: