Question

我必须创建一个程序，从两个已经按字母顺序排列的文件中读取名称和ID号，并将它们完全按字母顺序组合在第三个文件上。文件的组织方式如下......

姓氏，名字 ID（例如rbb091020）姓氏，名字 ID

由于某种原因，我的文件读取了两个文件并创建了第三个文件，但它没有向第三个文件写入任何内容。

这是我的代码......

import java.io.*;
import java.util.Scanner;

public class Combine_Files
{
public static void main(String[]args) throws IOException
{
    String filename1 = "";
    String filename2 = "";
    String combinedFileName = "";
    String response = "";
    String nextName1 = "";
    String nextName2 = "";
    String nextIDNumber1 = "";
    String nextIDNumber2 = "";
    boolean okToOverwrite = false;
    Scanner keyboard = new Scanner(System.in);

    System.out.println("What is the name of the first file?");
    filename1 = keyboard.nextLine();

    File file1 = new File(filename1);

    if (!file1.exists())
    {
        System.out.println(file1 + " does not exist.\nTerminating Program.");
        System.exit(0);
    }

    System.out.println("What is the name of the second file?");
    filename2 = keyboard.nextLine();

    File file2 = new File (filename2);
    if (!file2.exists())
    {
        System.out.println(file2 + " does not exist.\nTerminating Program.");
        System.exit(0);
    }   

    System.out.println("What is the name of the file that you wish to create?");
    combinedFileName = keyboard.nextLine();
    File combinedFile = new File (combinedFileName);

    while (combinedFile.exists() && !okToOverwrite)
    {
        System.out.println("\nError, a file named " +
            combinedFileName + " already exists." +
            "\nWould you like to overwrite this file?" +  
            "\nEnter Y for Yes or N for No.");
        response = keyboard.nextLine();

        // Add input validation on response

        if (response.equalsIgnoreCase("Y"))
        {
            okToOverwrite = true;
        }
        else 
        {
            System.out.println("Enter a new filename.");
            combinedFileName = keyboard.nextLine();
            combinedFile = new File(combinedFileName);
        }
    }

    if (file1.exists() && file2.exists())
    {

        Scanner list1 = new Scanner(file1);
        Scanner list2 = new Scanner(file2);
        PrintWriter outputFile = new PrintWriter(combinedFile);

            while (list1.hasNext() && list2.hasNext())
            {
                nextName1 = list1.nextLine();
                nextName2 = list2.nextLine();

                if(nextName1.compareToIgnoreCase(nextName2) <0)
                {
                    outputFile.print(nextName1);
                    nextName1 = list1.nextLine();
                    outputFile.print(nextName1);
                }
                else if(nextName1.compareToIgnoreCase(nextName2) >0)
                {
                    outputFile.println(nextName2);
                    nextName2 = list2.nextLine();
                    outputFile.println(nextName2);
                }
                else
                {
                    outputFile.println(nextName1);
                    nextName1 = list1.nextLine();
                    outputFile.println(nextName1);
                    outputFile.println(nextName2);
                    nextName2 = list2.nextLine();
                    outputFile.println(nextName2);
                }       
            }

            while (list1.hasNext() && !list2.hasNext())
            {
                outputFile.println(nextName1);
            }

            while (list2.hasNext() && !list1.hasNext())
            {
                outputFile.println(nextName2);
            }       
    }
}   
}

Answer 1

当您使用像PrintWriter这样的编写器类时，您需要确保每次要将某些内容打印到STDOUT或文件时调用flush()方法。所以基本上每当你调用它写入内部缓冲区的任何PrintWriter打印方法时，对flush()的调用就会将缓冲区发送到适当的输出流。

        while (list1.hasNext() && list2.hasNext())
        {
            nextName1 = list1.nextLine();
            nextName2 = list2.nextLine();

            if(nextName1.compareToIgnoreCase(nextName2) <0)
            {
                outputFile.print(nextName1);
                nextName1 = list1.nextLine();
                outputFile.print(nextName1);
            }
            else if(nextName1.compareToIgnoreCase(nextName2) >0)
            {
                outputFile.println(nextName2);
                nextName2 = list2.nextLine();
                outputFile.println(nextName2);
            }
            else
            {
                outputFile.println(nextName1);
                nextName1 = list1.nextLine();
                outputFile.println(nextName1);
                outputFile.println(nextName2);
                nextName2 = list2.nextLine();
                outputFile.println(nextName2);
            }
            outputFile.flush(); // <--- flush added here       
        }

        while (list1.hasNext() && !list2.hasNext())
        {
            outputFile.println(nextName1);
            outputFile.flush(); // <--- flush added here 
        }

        while (list2.hasNext() && !list1.hasNext())
        {
            outputFile.println(nextName2);
            outputFile.flush(); // <--- flush added here 
        }

对flush()的这些调用应该写入文件。

Answer 2

此程序存在逻辑错误。当我测试长度不均匀的文件时，它会在最后两个while循环之一中陷入无限循环，并且确实会写入输出文件，直到程序被强制终止。如果文件长度相同，则扫描程序无法读取其中一个if / else子句中的行。

为什么我的程序不会将信息写入文件？

2 个答案: