Question

我正在编写一个方法，它将接受一些命令行参数，验证它们，如果有效则会编辑机场的代码。机场名称及其代码存储在CSV文件中。一个例子是＆＃34;贝尔法斯特，BHD＆＃34;。命令行参数输入如下，java editAirport EA BEL Belfast，＆＃34; EA＆＃34;是2代码，使项目知道我想编辑机场的代码，＆＃34; BEL＆＃34;是新代码，贝尔法斯特是机场的名称。当我查看了这些文章并对其进行了验证后，我通读了该文件，并将它们存储在一个ArrayList中，如贝尔法斯特贝尔法斯特贝尔法斯特贝尔法斯特贝尔法斯特贝尔法斯特那样。然后我想通过删除文本文件中的行并转储到arraylist来更新文本文件，但我无法弄清楚如何做到这一点。有人可以使用简单的代码（没有高级的Java东西）向我展示如何实现这一点。这是我的程序

    import javax.swing.*;
    import java.io.*;
    import java.util.*;
    import java.text.*;
    public class editAirport
    {
      public static void main(String [] args)throws IOException
      {
        String pattern = "[A-Z]{3}";
        String line, line1, line2;
        String[] parts;
        String[] parts1;
        boolean found1 = false, found2 = false;
        File file = new File("Airports.txt"); // I created the file using the examples in the outline
        Scanner in = new Scanner(file);
        Scanner in1 = new Scanner(file);
        Scanner in2 = new Scanner(file);
        String x = args[0], y = args[1], z = args[2];
        //-------------- Validation -------------------------------
        if(args.length != 3) // if user enters more or less than 3 CLA's didplay message
          JOptionPane.showMessageDialog(null, "Usage: java editAirport EA AirportCode(3 letters) AirportName");
        else if(!(file.exists())) // if "Airports.txt" doesn't exist end program
            JOptionPane.showMessageDialog(null, "Airports.txt does not exist");
        else // if everything is hunky dory
        {
          if(!(x.equals("EA"))) //if user doesn't enter EA an message will be displayed
             JOptionPane.showMessageDialog(null, "Usage: java editAirport EA AirportCode(3 letters) AirportName");
          else if(!(y.matches(pattern))) // If the code doesn't match the pattern a message will be dislayed
            JOptionPane.showMessageDialog(null, "Airport Code is invalid");

          while(in.hasNext())
          {
             line = in.nextLine();
             parts = line.split(",");
             if(y.equalsIgnoreCase(parts[1]))
                found1 = true;  //checking if Airport code already is in use
             if(z.equalsIgnoreCase(parts[0]))
                found2 = true; // checking if Airport name is in the file
          }
          if(found1)
            JOptionPane.showMessageDialog(null, "Airport Code already exists, Enter a different one.");
          else if(found2 = false)
            JOptionPane.showMessageDialog(null, "Airport Name not found, Enter it again."); 
          else

            /*
            Creating the ArrayList to store the name,code.
            1st while adds the names and coses to arraylist, 
            checks if the name of the airport that is being edited is  in the line,
            then it adds the new code onto the name.
            sorting the arraylist.
            2nd for/while is printing the arraylist into the file
            */
            ArrayList<String> airport = new ArrayList<String>();
            while(in1.hasNext()) // 1st while
            {
                line1 = in1.nextLine();
                if(line1.contains(z))
                {
                    parts1 = line1.split(",");
                    parts1[1] = y;
                    airport.add(parts1[0] + "," + parts1[1]);
                }
                else
                    airport.add(line1);
            }
            Collections.sort(airport); // sorts arraylist
            FileWriter aFileWriter = new FileWriter(file, true);
            PrintWriter output = new PrintWriter(aFileWriter);
            for(int i = 0; i < airport.size();)
            {
                while(in2.hasNext()) // 2nd while
                {
                    line2 = in2.nextLine();
                    line2 = airport.get(i);
                    output.println(line2);
                    i++;
                }
            }
            output.close();
            aFileWriter.close();    
        }   
    }
}

}

Airports.txt文件是这个

    Aberdeen,ABZ
    Belfast City,BHD 
    Dublin,DUB 
    New York,JFK 
    Shannon,SNN 
    Venice,VCE

Answer 1

我认为你的问题可能在于两行：

line2 = in2.nextLine();
line2 = airport.get(i);

这会覆盖＆＃39; line2＆＃39;在内存中，但不在文件中。

如何使用ArrayList，Java更新文件

1 个答案: