如何在android中使用FileWriter数组：java.lang.NullPointerException:尝试写入null数组

我有多个文件要写入，因此我尝试使用

FileWriter

和

PrintWriter

数组。我甚至用try-and-catch来包围这些语句，但应用程序仍然崩溃并给出错误：

java.lang.NullPointerException:尝试写入空数组

这就是我所做的： 在主

活动中

类I声明了

文件编写器的数组

，以及

private FileWriter outStream[];
private PrintWriter printWriter[];

在

onCreate

函数中，我执行了以下操作：

try {
           outStream[0] = new FileWriter(finalFile_Acc, true);
           printWriter[0]= new PrintWriter(outStream[0]);
     } catch (IOException e) {
           e.printStackTrace();
     }
try {
           outStream[1] = new FileWriter(finalFile_Gyro, true);
           printWriter[1]= new PrintWriter(outStream[1]);
    } catch (IOException e) {
           e.printStackTrace();
    }

---

PS：我不能在同一个位置声明和初始化

文件编写器

和

打印编写器

。

对于打印编写器，您应该这样使用它

    PrintWriter printWriter[];
    int numberOfPrintWriters = 10;

    StringWriter stringWriter = new StringWriter();
    printWriter = new PrintWriter[numberOfPrintWriters];

    //using first printWriter
    PrintWriter printWriter[0] = new PrintWriter(stringWriter);
     try {
        printWriter[0].write(str, 0, 26);
        //or
        printWriter[0].print("ZZZ");
    }catch(Exception e){
      e.printStackTrace();
    }finally {
        printWriter[0].close();
    }

    //Similarly you can use other printWriters in array using their index like printWriter[i]

  int numberOfFileWriters = 10;
  FileWriter fWriter[];
  fWriter = new FileWriter[numberOfFileWriters];
  try{
     //using first fileWriter
     fWriter[0] = new FileWriter(file, true);
     fWriter[0].write("content");
     fWriter[0].flush();

  }catch(Exception e){
      e.printStackTrace();
  }finally{
     fWriter[0].close();
  }

  //Similarly you can use other fWriters in array using their index like fWriter[i]

对于FileWriter，您可以这样使用它

    PrintWriter printWriter[];
    int numberOfPrintWriters = 10;

    StringWriter stringWriter = new StringWriter();
    printWriter = new PrintWriter[numberOfPrintWriters];

    //using first printWriter
    PrintWriter printWriter[0] = new PrintWriter(stringWriter);
     try {
        printWriter[0].write(str, 0, 26);
        //or
        printWriter[0].print("ZZZ");
    }catch(Exception e){
      e.printStackTrace();
    }finally {
        printWriter[0].close();
    }

    //Similarly you can use other printWriters in array using their index like printWriter[i]

  int numberOfFileWriters = 10;
  FileWriter fWriter[];
  fWriter = new FileWriter[numberOfFileWriters];
  try{
     //using first fileWriter
     fWriter[0] = new FileWriter(file, true);
     fWriter[0].write("content");
     fWriter[0].flush();

  }catch(Exception e){
      e.printStackTrace();
  }finally{
     fWriter[0].close();
  }

  //Similarly you can use other fWriters in array using their index like fWriter[i]

如果您想在externalSDCard中写入文件，则

File file = new File(Environment.getExternalStorageDirectory() + " \filename.txt");

---

它是这样工作的，但我想使用FileWriter和PrintWriter数组。请参阅使用PrintWriter和FileWriter数组的修改答案。好的，谢谢，这很有效。只需添加这两行outStream=newfilewriter[2]；printWriter=新的printWriter[2]；