爲什麼檢索系統信息返回異常的零點？

Question

我已經裝盤得到與Runtime.getRuntime().exec(cmd);

系統的信息，我得到以下錯誤：

java.lang.NullPointerException 
    at java.lang.Runtime.exec(Runtime.java:422) 
    at java.lang.Runtime.exec(Runtime.java:326) 
    at mytest.SystemInfoToTextArea.doInBackground(SystemInfoToTextArea.java:31) 
    at mytest.SystemInfoToTextArea.doInBackground(SystemInfoToTextArea.java:16) 

任何建議歡迎類

代碼

public class SystemInfoToTextArea extends SwingWorker<String, Void> { 
private JTextArea textArea; 
private String cmd; 

public SystemInfoToTextArea(JTextArea textArea, String cmd) { 
    textArea = textArea; 
    cmd = cmd; 
} 

@Override 
protected String doInBackground() throws Exception { 
    String outputMem = null; 
    try { 
     String lineMem; 
     outputMem = ""; 
     Process procMem = Runtime.getRuntime().exec(cmd); 
     BufferedReader input = 
       new BufferedReader 
         (new InputStreamReader(procMem.getInputStream())); 
     while ((lineMem = input.readLine()) != null) { 
      outputMem = (lineMem + "\n"); 

     } 

     input.close(); 
    } catch (Exception err) { 
     err.printStackTrace(); 
    } 
    return outputMem; 
} 

@Override 
protected void done() { 
    super.done(); 
    try { 
     textArea.append(get()); 
    } catch (InterruptedException e) { 
     e.printStackTrace(); 
    } catch (ExecutionException e) { 
     e.printStackTrace(); 
    } 

} 

public static void main(String... args){ 
    JFrame frame = new JFrame(); 
    frame.setSize(700,500); 
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 

    JPanel panel = new JPanel(); 
    JTextArea textArea = new JTextArea("System info"); 

    panel.add(textArea); 
    frame.setContentPane(panel); 

    frame.setVisible(true); 

    SystemInfoToTextArea systemInfoToTextArea = new SystemInfoToTextArea(textArea,"cmd /C dir"); 
    systemInfoToTextArea.execute(); 

} 
} 

Answer 1

你cmd一世顯然是null，因爲你的構造函數代碼是錯誤的。寫

this.cmd = cmd; 

相同的textArea。

Answer 2

您的構造並不做你認爲：

public SystemInfoToTextArea(JTextArea textArea, String cmd) { 
    textArea = textArea; 
    cmd = cmd; 
} 

這只是重新分配的參數，並且不設置領域具有相同名稱（自己的價值觀！）。你想要做的是用它作爲前綴：

public SystemInfoToTextArea(JTextArea textArea, String cmd) { 
    this.textArea = textArea; 
    this.cmd = cmd; 
} 

體面的IDE會警告你這個錯誤。