java - 扫描仪不读取文件内容

Question

我试图在第一次创建一个名为 amountSessions 的文件时将数字 0 写入该文件，正如您在注释“第一次运行”下面的 if 语句中看到的那样，该语句到目前为止有效，但稍后在程序中(在 writeToFile 方法的末尾)在注释“每次运行增加数字”下面，我想在每次程序运行时将我之前讨论的 0 加 1。不幸的是，当我编译并运行该程序时，出现以下错误。为什么是这样？非常感谢大家!

Exception in thread "main" java.util.NoSuchElementException
at java.util.Scanner.throwFor(Scanner.java:862)
at java.util.Scanner.next(Scanner.java:1485)
at java.util.Scanner.nextInt(Scanner.java:2117)
at java.util.Scanner.nextInt(Scanner.java:2076)
at math_program.fileWriting.getInt(fileWriting.java:62)
at math_program.fileWriting.writeToFile(fileWriting.java:41)

//Test

package testing;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileWriter;
import java.io.IOException;
import java.util.Scanner;
import javax.swing.JOptionPane;

public class Kappa
{
    String numberFilePath = "/Users/john/Desktop/numProblems.txt";
    String sessionFilePath = "/Users/john/Desktop/amountSessions.txt";
    File testFile = new File(numberFilePath);
    File amountSessions = new File(sessionFilePath); 

    public void writeToFile() throws IOException
    {

        //On the first run
        if(!testFile.exists())
        {
            testFile.createNewFile();
        } else if(!amountSessions.exists())
        {
            amountSessions.createNewFile();
            FileWriter sessionWriter = new FileWriter(amountSessions);
            sessionWriter.write("0");
            sessionWriter.close();
        }

        FileWriter durationWriter = new FileWriter(testFile);
        FileWriter sessionWriter = new FileWriter(amountSessions);

        //Write Duration
        String ans = prompt();
        durationWriter.write(ans);
        durationWriter.close();

        //Increment number each run
        sessionWriter.write(getInt());
        sessionWriter.close();

        System.exit(0); 
    }

    public void grab() throws FileNotFoundException
    {
        Scanner numProblemsReader = new Scanner(new File("/Users/john/Desktop/numProblems.txt"));
        Scanner numSessionReader = new Scanner(new File("/Users/john/Desktop/amountSessions.txt"));
        int number = numProblemsReader.nextInt();
        int numSessions = (numSessionReader.nextInt() + 1);

        System.out.println("The number read from the file is: " + number);
        File replaceFile = new File("/Users/john/Desktop/session" + numSessions + ".txt");
        testFile.renameTo(replaceFile);
    }

    public String getInt() throws FileNotFoundException
    {
        Scanner numSessionReader = new Scanner(new File("/Users/john/Desktop/amountSessions.txt"));
        int numSessions = ((numSessionReader.nextInt()) + 1);
        String newNum = Integer.toString(numSessions);
        return newNum;
    }

    public String prompt()
    {
        String ans = JOptionPane.showInputDialog ("Enter the new amount of problems per training session (with number in minutes):");                        

        while(!ans.matches("[0-9]+"))
        {
            ans = JOptionPane.showInputDialog ("Please re-enter the new amount of problems per training session (with number in minutes):" ); 
        }    

        return ans;
    }
}

Answer 1

改变

} else if(!amountSessions.exists())

至

}
if(!amountSessions.exists())

否则，如果两者都不存在，则仅创建第一个文件。