[英]Java Exception problem with scanner and method
我在 java 中遇到了一些問題,在 while 循環中將掃描儀放在輸出之后。 掃描器掃描要使用的方法,然后當它回到循環開始時重置變量。
我已經嘗試過這個,但沒有找到任何可以理解的解決方案(我對 Java 真的很陌生,這對我來說很難),或者自己解決。 這是完整的代碼(我知道代碼效率不高):
import java.util.Scanner;
public class Main {
public static void main(String[] args) {
int con = 1;
System.out.println("Hey!,welcome to my games!");
Scanner scanner = new Scanner(System.in);
String game;
while (con == 1) {
System.out.println(
"Here Some games i have(Enter the text for the one you want):\nto stop=0\n1)calculator=1\n2)!Soon! Random numbers");
game = scanner.nextLine();
calculator();
scanner.reset();
System.out.println(game);
// if(game.equals("0")) {
// con=0;
// }
// else if(game.equals("1")) {
// System.out.println("Welcome Back!");
// }
// else {
// System.out.println("There is a mistake in your text");
// }
}
scanner.close();
}
static void calculator() {
int num1, num2, con = 1, stop = 1;
String op, ad = "add", su = "sub", mul = "multi", di = "div";
Scanner af = new Scanner(System.in);
while (con == 1) {
stop = 1;
System.out.println("Write number 1");
num1 = af.nextInt();
System.out.println("Write number 2");
num2 = af.nextInt();
System.out.println(
"Write an operation (one of these):\nAddition=add\nSubtraction=sub\nMultiplication=multi\nDivision=div");
op = af.next();
op = op.toLowerCase();
int minus = num1 - num2;
int plus = num1 + num2;
if (op.equals(ad)) {
System.out.println("The Operation is:Addition\n" + num1 + "+" + num2 + "=" + plus);
} else if (op.equals(su)) {
System.out.println("The Operation is:Subtraction\n" + num1 + "-" + num2 + "=" + minus);
} else if (op.equals(mul)) {
System.out.println("The Operation is:Multiplication\n" + num1 + "*" + num2 + "=" + num1 * num2);
} else if (op.equals(di)) {
System.out.println("The Operation is:Division\n" + num1 + "/" + num2 + "=" + num1 / num2);
} else {
System.out.println("Um,Did you make a mistake in your text?\nDo you want the calculator again?");
String yn = af.next();
yn = yn.toLowerCase();
if (yn.equals("yes") || yn.equals("yep")) {
stop = 0;
}
}
if (stop == 1) {
con = 0;
}
}
af.close();
}
}
如您所見,我嘗試自己解決它,甚至對一些代碼進行了注釋,但是當它運行到該方法並返回時,它失敗了,因為掃描儀認為在我寫一些東西之前有一些東西要掃描。 這是例外-
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:1478)
at Main.main(Main.java:12)
do-while
循環,它保證至少執行一次其主體。 查看本教程以了解更多信息。Scanner::nextLine
而不是Scanner::next
、 Scanner::nextInt
等,因為它們不使用輸入中通過按Enter鍵創建的換行符。 查看此討論以了解更多信息。System.in
的Scanner
,因為它也會關閉System.in
並且無法在不重新啟動 JVM 的情況下再次打開它。 注意:如果您使用Scanner
掃描File
,請確保關閉它以釋放資源。演示:
import java.util.Scanner;
public class Main {
public static void main(String[] args) {
int option;
boolean valid;
Scanner input2 = new Scanner(System.in);
do {
valid = true;
System.out.println("Choose an option:\n" + "1-Addition\n" + "2-Subtraction\n" + "3-Exit");
try {
option = Integer.parseInt(input2.nextLine());
if (option < 1 || option > 3) {
throw new IllegalArgumentException();
}
// ...Place here the rest of code (which is based on the value of option)
} catch (IllegalArgumentException e) {
System.out.println("This is an invalid entry. Please try again.");
valid = false;
}
} while (!valid);
}
}
示例運行:
Choose an option:
1-Addition
2-Subtraction
3-Exit
x
This is an invalid entry. Please try again.
Choose an option:
1-Addition
2-Subtraction
3-Exit
10.5
This is an invalid entry. Please try again.
Choose an option:
1-Addition
2-Subtraction
3-Exit
1
你記得導入 java.util.Scanner 嗎? 或者你如何編譯你的源文件? 用 gradle 編譯時我有同樣的錯誤消息,我在 gradle 構建文件中遺漏了一小行。
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