Question

我有多个要写入的文件，因此我尝试使用FileWriter和PrintWriter的数组。我甚至用try和catch包围了这些语句，但是应用程序仍崩溃并给出了错误：

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

这就是我所做的：在主Activity类中，我声明了一个FileWriter和

的数组

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

在onCreate函数中我做了这个：

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：我无法在同一位置声明并初始化FileWriter和PrintWriter。

Answer 1

对于PrintWriter，您应该像这样使用它

    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]

对于FileWriter，您可以像这样使用它

  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]

如果要在externalSDCard中写入文件，那么

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

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

1 个答案: