问题描述
该程序的基础是要有一个菜单,该菜单会导致需要完成的各种不同“课程”。 toMenu()方法将运行并正确地将值返回给main方法,并且 method3_13()的开始文本指出“请在下面输入一个正整数: ”,但之后会显示错误消息。这是错误消息:
Exception in thread "main" java.util.NoSuchElementException
at java.base/java.util.Scanner.throwFor(Scanner.java:937)
at java.base/java.util.Scanner.next(Scanner.java:1594)
at java.base/java.util.Scanner.nextInt(Scanner.java:2258)
at java.base/java.util.Scanner.nextInt(Scanner.java:2212)
at Chapter3ShortAnswers.method3_13(Chapter3ShortAnswers.java:67)
at Chapter3ShortAnswers.main(Chapter3ShortAnswers.java:15)
下面是我到目前为止编写的代码...请帮助;〜;
import java.util.Scanner;
public class Chapter3ShortAnswers {
public static void main(String []args) {
int lesson = toMenu(); //takes user to menu and returns user-inputted value
switch (lesson) { // switch statement that leads the user to each method's lesson
case 0: System.out.println("Thank you for running this program! Have a great day!");
case 1: method3_13();
case 2:
case 3:
case 4:
case 5:
case 6:
case 7:
case 8:
}
}
/**
* FINSH THIS AT THE END
* pre: none
* post: returns number to lesson
* while: accept user input number
*/
public static int toMenu() {
Scanner input = new Scanner(system.in);
int chapterNum;
System.out.println("Table of Contents ... Please type the number adjacent to the Lesson you would like to visit \n(Press 0 to go back to the menu,press 0 again to end the program): \n");
System.out.format("%-10s %8s","Lesson","Input Number\n"); // each lesson has a respective number the user
// this is the number the user inputs
System.out.format("%-10s %8s","3.13","1\n");
System.out.format("%-10s %8s","3.14","2\n");
System.out.format("%-10s %8s","3.15","3\n");
System.out.format("%-10s %8s","3.16","4\n");
System.out.format("%-10s %8s","3.18","5\n");
System.out.format("%-10s %8s","3.19","6\n");
System.out.format("%-10s %8s","3.20","7\n");
System.out.format("%-10s %8s","3.21","8\n");
System.out.println("\nType your number here: ");
chapterNum = input.nextInt();
input.close();
return chapterNum; // returns the user inputed number back to the main menu,which assigns it to variable "lesson"
}
/**
*
*/
public static void method3_13() {
int chapterNum = 0;
int user;
Scanner input = new Scanner(system.in);
System.out.println("Please enter a positive integer below: ");
user = input.nextInt();
if(user % 1 == 0 && user >= 0) {
System.out.println("Thank you for entering a number! To go back to the menu and choose another lesson,press 0. ");
} else {
while (user % 1 != 0 || user < 0) {
if(user % 1 != 0) {
System.out.println("This is not an integer. Please try again with an integer.");
} else if (user < 0) {
System.out.println("This is not a positive ineger. Please try again with a positive integer");
} else if (user % 1 != 0 && user < 0) {
System.out.println("This is not an integer,nor is it positive. Please try again with a positive integer.");
}
}
if (user % 1 == 0) {
System.out.println("Thank you for entering a number! To go back to the menu and choose another lesson,press 0.");
chapterNum = input.nextInt();
if(chapterNum == 0) {
toMenu();
}
}
}
input.close();
}
}
解决方法
@Mert是正确的,Scanner将关闭基础流(如果可关闭),并且由于您在实例化另一个Scanner时正在使用System.in,因此实际上是在传递闭合流,从而传递NotSuchElementException。请注意nextInt()的扫描仪文档:
@如果输入已用尽,则抛出NoSuchElementException。
对于close():
如果此扫描器尚未关闭,则如果其底层可读文件也实现了Closeable接口,则将调用该可读文件的close方法。
因此,只需在应用程序结束时关闭扫描仪即可。
,问题是您要使用toMenu方法中的input.close()关闭扫描仪,然后尝试再次使用扫描仪。你不能那样做。
尝试一下:
public static int toMenu() {
Scanner input = new Scanner(System.in);
int chapterNum;
System.out.println("Table of Contents ... Please type the number adjacent to the Lesson you would like to visit \n(Press 0 to go back to the menu,press 0 again to end the program): \n");
System.out.format("%-10s %8s","Lesson","Input Number\n"); // each lesson has a respective number the user
// this is the number the user inputs
System.out.format("%-10s %8s","3.13","1\n");
System.out.format("%-10s %8s","3.14","2\n");
System.out.format("%-10s %8s","3.15","3\n");
System.out.format("%-10s %8s","3.16","4\n");
System.out.format("%-10s %8s","3.18","5\n");
System.out.format("%-10s %8s","3.19","6\n");
System.out.format("%-10s %8s","3.20","7\n");
System.out.format("%-10s %8s","3.21","8\n");
System.out.println("\nType your number here: ");
chapterNum = input.nextInt();
return chapterNum; // returns the user inputed number back to the main menu,which assigns it to variable "lesson"
}
请确保在使用完扫描仪后始终将其关闭。