Question

这是一个大学课程作业，由TotalSales和TotalSalesTest类组成。在主程序中，我创建了一个二维数组，用于输出一个包含4行和5列交叉总数的列式布局。该程序为每个销售人员（1 - 4）逐行输出销售总额，并按产品（1-5）的列输出。我在数组中创建了额外的元素来存储行和列的总数。到目前为止，两个类都编译。问题是虽然PrintWriter创建了一个记事本文件，但它不会打印到它。我可以在这个问题上使用一些帮助。这是代码`

 //write program in a two diminsional array to output a columnar layout with cross-totals in 4 rows and 5 columns
 //program outputs sales totals by row for each sales person(1 - 4) and output by column for products(1 - 5)
 //create extra elements to store total for rows and columns 
 import java.util.Scanner;
 import java.io.*;
 public class TotalSales
 {
 private int salesPerson; //declare class variable  
 private int productNumber;//declare class variable
 private double totalSales;//declare class variable
 private double allSales;
//declare input and output variables
Scanner inFile; //declare inFile variable 
PrintWriter outFile;//declare outFile variable 



  double[][]sales = new double[6][7];//declare array sales


  public void initializer()
  {
  try
  {
  inFile  = new Scanner( new File( "assign06.txt" ) );
  outFile = new PrintWriter( "MonthlyTotalSales.txt" );
  outFile.flush(); 
  }
  catch (FileNotFoundException e)
  {
     System.out.println("The input file could not be found!");
     System.exit(1); 
  }

 while(inFile.hasNext()) //while there is data to process… 
  {
 salesPerson = inFile.nextInt();//reads salesPerson
 productNumber = inFile.nextInt();//reads productNumber
 totalSales = inFile.nextDouble();//reads totalSales
 sales[salesPerson][productNumber]+=totalSales;

 sales[salesPerson][6]+=totalSales;

 sales[5][productNumber]+=totalSales;

 allSales += totalSales;
  } //end while loop
 printDetails(sales);//call method printDetails
 finishUp();//call method finishUp

 }//end initializer

 public void printDetails(double[][] array)
 {
outFile.println("\t1\t2\t3\t4\t5");

 for (int salesPerson =1; salesPerson <5; salesPerson++)
{
  outFile.print(salesPerson+ "      ");
  for(int productNumber=1; productNumber <=array.length; productNumber++)
     outFile.print(array[salesPerson][productNumber]+"    ");

  //end inside loop
  outFile.println();
 }//end outside loop


 outFile.print("Total: \t  ");
 for(int salesTotal=1; salesTotal<array.length; salesTotal++)
 {   
  outFile.print(array[5][salesTotal] +" ");
 }
 outFile.print(allSales);


 outFile.println();


    outFile.print("  ");        

    outFile.println();

  }//end printDetails

 public void finishUp()
 {
 inFile.close();
 outFile.close();
 System.out.println("The program has finished.");

 }//end finishUp

}//end class TotalSales

以下是测试程序：

public class TotalSalesTest
{
    public static void main(String[] args)
    {
        TotalSales ts = new TotalSales();
        ts.initializer();
    }//end method main
}

以下是输入的文本文件：

Answer 1

在初始化作者之前致电printDetails ...在printDetails之后移动outFile = new PrintWriter( "MonthlyTotalSales.txt" );来电，应该没问题。但是，你应该包含你的构造函数，因为它现在是，我认为你的代码抛出NullPointerException，因为编写器从未被初始化。您还需要在写入之前关闭文件，或者至少需要刷新。

你的代码的整个结构都很糟糕，你不应该在类上有mainProgram这样的方法，你不应该只使用文件作为属性来在每个方法中使用它，你永远不应该在不同方法中分离创建和关闭i / o类。

Answer 2

似乎你没有调用outFile.close（）;

完成文件写入后，请调用finishUp（）方法。

Answer 3

我认为您的程序在

上使用nullpointer崩溃了

inFile.hasNext（）

因为你从未实际打开过甚至实例化输入文件以及try / catch块中的输出文件。糟糕！

变化

    try
    {
        outFile = new PrintWriter( "MonthlyTotalSales.txt" ); 
    }

到

    try
    {
        inFile = new Scanner(new File("Input.txt"));
        outFile = new PrintWriter( "MonthlyTotalSales.txt" ); 
    }

PrintWriter创建文件但不打印到文件

3 个答案: