如何獲取JTextField以顯示文件中的文本

Question

我正在爲計算機類製作一個簡單的「腳本解釋器」，並且我希望當前在JTextField中顯示文件的內容，但我一直在空指針異常。 下面是代碼：

MainClass（它是由發射器類與主方法運行）

package ClydeInterpreter; 

import Input.ButtonManager; 

import gfx.Display; 

public class Interpreter extends Thread 
{ 
    private Handler handler; 
    private Display display; 
    private ButtonManager buttonManager; 

public Interpreter() 
{ 
    System.out.println("Interpreter is created"); 
    buttonManager = new ButtonManager(this); 
    handler = new Handler(this, buttonManager); 
    display = new Display(handler); 
    buttonManager.Update(this); 
    handler.Update(this); 
} 



public Handler getHandler() 
{ 
    return handler; 
} 



public void setHandler(Handler handler) 
{ 
    this.handler = handler; 
} 



public Display getDisplay() 
{ 
    return display; 
} 

public void setDisplay(Display display) 
{ 
    this.display = display; 
} 

} 

我的處理程序：

package ClydeInterpreter; 

import FileReader.FileInput; 
import Input.ButtonManager; 

public class Handler 
{ 
    private Interpreter interp; 
    private ButtonManager buttonManager; 

public Handler(Interpreter interp, ButtonManager buttonManager) 
{ 
    this.interp = interp; 
    this.buttonManager = buttonManager; 
} 

public Interpreter getInterp() 
{ 
    return interp; 
} 

public void setInterp(Interpreter interp) 
{ 
    this.interp = interp; 
} 

public ButtonManager getButtonManager() 
{ 
     return buttonManager; 
} 

public void setButtonManager(ButtonManager buttonManager) 
{ 
     this.buttonManager = buttonManager; 
} 


public void Update(Interpreter interpreter) 
{ 
    this.interp = interpreter; 
} 

}

我的FileInput類（讀取並輸出文件內容的類）：

package FileReader; 

import java.io.BufferedReader; 
import java.io.File; 
import java.io.FileInputStream; 
import java.io.FileNotFoundException; 
import java.io.FileReader; 
import java.io.IOException; 

import ClydeInterpreter.Handler; 
import ClydeInterpreter.Utils.Utils; 
public class FileInput 
{ 
FileInputStream fileReader; 
Handler handler; 
public FileInput(Handler handler) 
{ 
    this.handler = handler; 
} 

public void ReadFile(File file) 
{ 
    try { 
     BufferedReader in = new BufferedReader(new FileReader(file)); 
     StringBuffer stringBuffer = new StringBuffer(); 
     String str, line; 
     while ((str = in.readLine()) != null) 

      //stringBuffer.append("\n"); 
      process(str); 
     in.close(); 
    } catch (IOException e) { 
    } 
} 

private void process(String str) 
{ 
    System.out.println(str); 
    handler 
    .getInterp() 
    .getDisplay() 
    .getConsole() 
    .setText(str); 
} 

}

的Button Manager類（如文件輸入初始化）：

package Input; 

import java.awt.*; 
import javax.swing.*; 
import java.awt.event.*; 
import javax.sound.sampled.*; 
import java.io.*; 
import java.net.*; 

import javax.sound.sampled.AudioSystem; 
import javax.swing.JOptionPane; 

import ClydeInterpreter.Handler; 
import ClydeInterpreter.Interpreter; 
import ClydeInterpreter.Utils.Utils; 
import FileReader.FileInput; 
import gfx.Display; 

public class ButtonManager implements ActionListener 
{ 
Handler handler; 
static Interpreter interpreter; 
static Display display; 
static String loc; 
static FileInput fileInput; 
public ButtonManager(Interpreter interpreter) 
{ 
    this.interpreter = interpreter; 
    this.display = interpreter.getDisplay(); 
    this.fileInput = new FileInput(interpreter.getHandler()); 
} 

@Override 
public void actionPerformed(ActionEvent ae) 
{ 
    String dest; 
if (ae.getActionCommand().matches("open")) 
    { 
     FileDialog fd = new FileDialog(display.getF(), "Select Script", FileDialog.LOAD); 
     fd.setSize(300, 300); 
     fd.setVisible(true); 
     String s1 = ".clyde"; 
     /* 
     fd.setFilenameFilter(new FilenameFilter() 
     { 
      @Override 
      public boolean accept(File dir, String name) 
      { 
       return name.endsWith(".txt"); 
      } 
     }); 
     */ 
     String sng = fd.getFile(); 
     dest = fd.getDirectory() + fd.getFile(); 
     if (sng.toLowerCase().endsWith(s1)) 
     { 
      display.getTf().setText(sng); 
      display.setFile(new File(dest)); 


      //Utils.loadFileAsString(loc); 
     } 
     else 
     { 
      JOptionPane.showMessageDialog(display.getF(), "Select a valid file format"); 
     } 

     try 
     { 
      display.setFile(new File(dest)); 
     } catch (Exception e) 
     { 
      e.printStackTrace(); 
     } 
    } 

    else if(ae.getActionCommand().equals("debug")) 
    { 
     System.out.println("It works"); 
    } 

    else if (ae.getActionCommand().equals("run")) 
    { 
     fileInput.ReadFile(display.getFile()); 
    } 

} 

public void Update(Interpreter interpreter) 
{ 
    display = interpreter.getDisplay(); 
} 



} 

以下是錯誤：

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException at FileReader.FileInput.process(FileInput.java:40) at FileReader.FileInput.ReadFile(FileInput.java:30) at Input.ButtonManager.actionPerformed(ButtonManager.java:84) at javax.swing.AbstractButton.fireActionPerformed(Unknown Source) at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source) at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source) ...

如果有人能告訴我在哪裏，我搞砸了，或者更好的方式來做到這一點，這將是偉大的。提前致謝。

編輯 -I'm不問什麼是空指針，我問爲什麼我的handler.getInterp（）方法返回null。我忘了初始化它在哪裏。

Answer 1

java.lang.NullPointerException at

FileReader.FileInput.process(FileInput.java:40) at

您還沒有提供，你必須初始化FileReader.FileInput類的代碼和調用的方法process(String)但是你handler參考可能與null值 或handler.getInterp()被返回null值

handler 
.getInterp() 

初始化編輯：

第二次檢查

更新您的ButtonManager構造函數代碼，以檢查是否有非空處理或不

public ButtonManager(Interpreter interpreter) 
{ 
    this.interpreter = interpreter; 
    this.display = interpreter.getDisplay(); 
    // DEBUG CODE START 
    System.out.println("#### Handler : " + interpreter.getHandler()); 
    System.out.println("#### Interp : " + interpreter.getHandler().getInterp()); 
    // DEBUG CODE END 
    this.fileInput = new FileInput(interpreter.getHandler()); 
} 

如果SYSOUT空值，然後糾正它。

Answer 2

也許這將工作

try 
    { 
     FileReader file = new FileReader(".txt") ; 

     BufferedReader buffer = new BufferedReader(file); 

     String line = "" ; 

     while((line = buffer.readLine()) != null) 
     { 
      txt.setText(line) ; 
     } 

     buffer.close() ; 
    } 
    catch(IOException e) 
    { 
     System.out.println("A read error has occurred.") ; 
    }