我正在尝试打开,关闭和写入文件。每当我尝试打开文件时,如果它在我提供的路径中不存在,程序会告诉我。如果它存在,程序将读取内部的任何内容并显示它。如果用户不想查找文件,则可以选择创建文件并用数据填充。
它的工作原理到目前为止除了每当我读取文件时,在成功显示数据后,我得到一个未知的源扫描程序异常。到目前为止,这是我的代码:
import java.util.Scanner;
import java.io.File;
import java.io.IOException;
import java.io.PrintWriter;
public class FileIO {
public static void main(String[] args) throws IOException{
Scanner input = new Scanner(System.in);
while (true){
System.out.println("1. Load file from path of your choosing.");
System.out.println("2. Answer eight questions and save the answers into a file.");
System.out.println("3. Exit the program.");
int userChoice = input.nextInt();
switch (userChoice){
case 1:
loadFile();
break;
case 2:
answerQuestions();
break;
case 3:
System.out.println("Goodbye!");
break;
}
}
}
public static void loadFile() throws IOException{
System.out.println("What is the file name you want to try to read?");
Scanner input = new Scanner(System.in);
File f = new File(input.nextLine());
if (f.exists() && !f.isDirectory()){
System.out.println("The file exists!");
Scanner inputFile = new Scanner(f);
while (inputFile.hasNext()){
String answer = inputFile.next();
System.out.println(answer);
}
input.close();
}
else {
System.out.println("File does not exist at that given path!");
}
}
public static void answerQuestions() throws IOException{
Scanner input = new Scanner(System.in);
System.out.println("What is your name?"); // 1
String name = input.nextLine();
System.out.println("What is your favorite color?"); // 2
String color = input.nextLine();
System.out.println("What is your favorite type of music?"); // 3
String music = input.nextLine();
System.out.println("What is your favorite place?"); // 4
String place = input.nextLine();
System.out.println("What is your favorite food?"); // 5
String food = input.nextLine();
System.out.println("What is your favorite book?"); // 6
String book = input.nextLine();
System.out.println("What is your favorite programming language?"); // 7
String language = input.nextLine();
System.out.println("Do you prefer laptop or desktop computers?"); // 8
String computer = input.nextLine();
System.out.println("All the questions are answered. Name the file you want to save the answers to: ");
File f = new File(input.nextLine());
if (f.exists()){
System.out.println("File already exists!");
return;
}
PrintWriter output = new PrintWriter(f);
output.print(name + "\n");
output.print(color + "\n");
output.print(music + "\n");
output.print(place + "\n");
output.print(food + "\n");
output.print(book + "\n");
output.print(language + "\n");
output.print(computer + "\n");
output.close();
}
}
这是错误:
Exception in thread "main" java.util.NoSuchElementException
at java.util.Scanner.throwFor(Unknown Source)
at java.util.Scanner.next(Unknown Source)
at java.util.Scanner.nextInt(Unknown Source)
at java.util.Scanner.nextInt(Unknown Source)
at Lab4.main(Lab4.java:18)
究竟是什么问题?我尝试将第19行的扫描仪输入更改为input2,但这不起作用。该程序允许我选择尽可能多的菜单选项,如果在检查路径时文件不存在,所以我猜测程序在开始将内容打印到控制台的部分有问题(如果找到文件) 。但我不知道它可能是什么。我将不胜感激任何指导我处理此错误的提示或提示。谢谢你的时间。
答案 0 :(得分:1)
Scanner input = new Scanner(System.in);
/* other code here */
input.close();
关闭扫描仪也会关闭它使用的流。您已关闭System.in
。就像任何其他流一样,如果关闭,您就无法使用它。
理想的解决方案是创建一次扫描程序(在程序开始时),然后在每次想要读取输入时使用它。
答案 1 :(得分:0)
从input.close();
函数中删除loadFile()
,因为它关闭了引用的标准输入流,阻止了进一步的IO。