Question

我正在尝试写一个程序的问题。我正在使用一个arraylist来存储字符串，并且在访问它时遇到问题并将其写入带有其他数据集的输出文件，以便它们形成统一的列。我遇到的问题是当我尝试访问arraylist中的数据并将其增加时，我得到的是数字1-10而不是实际的数据集。这是我的代码和输出文件。

import java.util.ArrayList;
import java.text.DecimalFormat;
import java.util.Scanner;
import java.io.*;

public class RobertGardner_6_12
{
   public static void main(String[] args) throws IOException
   {
      // Declare variables
      // File names
      final String INPUT_FILE_NAME = "RobertGardner_6_12_Input.txt";
      final String OUTPUT_FILE_NAME = "RobertGardner_6_12 _Output.txt";

      // Append current file boolean variable
  final boolean APPEND_INDICATOR = false; // Create a new file

  double savings = 0;     // The sum of the numbers
  double debt = 0;        // 20% towards debt
  double moneyForYou = 0; // 70% for spending
  double oneNumber = 0;   // A single number read from the file
  String processPhrase;   // Indicates appending or creating a file

  // Access the input and output files
  try
    {
        File inputDataFile = new File(INPUT_FILE_NAME);
        Scanner inputScanner = new Scanner(inputDataFile);
    }
    catch( FileNotFoundException e)
    {
        System.err.println( "Error opening file.");
    }
  File inputDataFile = new File(INPUT_FILE_NAME); //Access input
  Scanner inputScanner = new Scanner(inputDataFile);
  FileWriter outputDataFile = new FileWriter(OUTPUT_FILE_NAME, 
  APPEND_INDICATOR);
  PrintWriter outputFile = new PrintWriter(outputDataFile);

  // Access the Toolkit using the variable 'tools'
  Toolkit_General tools = new Toolkit_General();

  // Format numeric output
  DecimalFormat formatter = new DecimalFormat("#,##0.00");

  if(APPEND_INDICATOR)
     processPhrase = "Appending";
  else
     processPhrase = "Creating";

  // Display file information on console
  System.out.println("Reading file " + INPUT_FILE_NAME + "\n"
  + processPhrase + " file " + OUTPUT_FILE_NAME + "\n");

  // Display heading in output file
  if (inputScanner.hasNext())
  {
     outputFile.println("Yearly Income Report");
     outputFile.println("-----------------------");
  }

  outputFile.println("Name               Income    10% saved    " +
                      "20% to debt        Yours to spend");
  outputFile.println("------------------------------------------" +
                      "----------------------------------");
  ArrayList<String> list = new ArrayList<String>();
  list.add("Donald");
  list.add("Jean");
  list.add("Christopher");
  list.add("Martin");
  list.add("Thomas");
  list.add("Samuel");
  list.add("George");
  list.add("Quentin");
  list.add("Magaret");
  list.add("Toby");

  int nameCounter = 0; // 
  // Read the input file and sum the numbers
  while (inputScanner.hasNext())
  {
     oneNumber = inputScanner.nextDouble();
     savings = oneNumber * .1;
     debt = oneNumber * .2;
     moneyForYou = oneNumber *.7;
     list.get(nameCounter);
     nameCounter++;

     outputFile.println(nameCounter + tools.leftPad(oneNumber, 18, "#0", " ") +    
tools.leftPad(savings, 18, "#0", " ")
    + tools.leftPad(debt, 18, "#0", " ") + tools.leftPad(moneyForYou, 18, "#0", " "));
  }

  // Close files
  outputFile.close();
  inputScanner.close();

} //结束主要

} //结束课

当我输出数据时，它看起来像这样：

1 100000 10000 20000 70000

当我想要输出时说：

唐纳德100000 10000 20000 70000

使用arraylist中的所有字符串

等等。

Answer 1

int nameCounter = 0;
while (inputScanner.hasNext()) {
    //...
    list.get(nameCounter); //<-- This line returns something. 
                           //    But you never keep a reference to it!
                           //    So how do you expect to do anything with it?
    nameCounter++;
    //...
}

当我尝试访问arraylist中的数据并将其递增时“

您无法增加Strings。

我得到的只是数字1-10

那是因为在这里：

outputFile.println(nameCounter + tools.leftPad(...)...);
                   ^^^^^^^^^^^

您正在打印nameCounter，而不是您想要的名称

您可能要做的是将list.get(nameCounter)的值保存到String，然后在打印语句中使用该变量而不是nameCounter。

Answer 2

从list检索值时，不将其保存到变量

尝试

  String name = list.get (nameCounter);
  outputFile.println (name + ....

同时更改此代码

  // Access the input and output files
    try {
        File inputDataFile = new File(INPUT_FILE_NAME);
        Scanner inputScanner = new Scanner(inputDataFile);
    } catch (FileNotFoundException e) {
        System.err.println("Error opening file.");
    }
    File inputDataFile = new File(INPUT_FILE_NAME); //Access input
    Scanner inputScanner = new Scanner(inputDataFile);

到

  // Access the input and output files
    Scanner inputScanner = null;
    try {
        File inputDataFile = new File(INPUT_FILE_NAME);
        inputScanner = new Scanner(inputDataFile);
    } catch (FileNotFoundException e) {
        System.err.println("Error opening file.");
        e.printStackTrace();
        return;  // no point in continuing
    }

使用get命令访问arraylist并输入java中的输出文件

2 个答案: