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[英]How do I get this block of code to keep looping until a correct student number is entered?
[英]How do i make the program keep looping until the user has entered an integer
我正在嘗試修改程序,以便即使用戶輸入了字符串而不是程序崩潰,它也應繼續循環並要求用戶輸入必須為整數的考試成績,僅當用戶輸入了整數,程序應終止。 我指的是do-while塊中的代碼
import java.util.InputMismatchException;
import java.util.Scanner;
public class CatchingException {
public static void main(String[] args) {
Scanner scan = new Scanner(System.in);
int score;
String choice;
try {
System.out.println("Enter your percentage mark: ");
score = scan.nextInt();
do {
if(score <40) {
System.out.println("You FAILED");
}else if(score >=40 && score <50){
System.out.println("Your grade: PASS MARK");
}else if(score >=50 && score <60) {
System.out.println("Your grade: 2:2");
}else if (score >=60 && score <70) {
System.out.println("Your grade: 2:1");
}else {
System.out.println("Your grade: 1:1");
}
System.out.println("Do you want to enter another grade: ");
choice = scan.next();
if(choice.equalsIgnoreCase("yes")) {
System.out.println("Enter your percentage mark: ");
score = scan.nextInt();
System.err.println("Incorrect Input");
}
}while();
}catch(InputMismatchException e) {
System.err.println("Incorrect Input ");
}
System.out.println("program terminated");
scan.close();
}
}
使用布爾變量來跟蹤是否繼續循環。 例如:
boolean loop = true;
do {
// set loop to false when you want to end
} while(loop);
所以你可以這樣做:
int score = null;
boolean isInt = false;
do {
System.out.println("Enter your percentage mark:");
try {
score = scan.nextInt();
isInt = true;
} catch (InputMismatchException e) {
//Not An Integer
isInt = false;
}
} while(false)
//Do you if statements here if it gets out of the while loop which means the user entered an int
相反的假設inputed數為int
,你可以輸入它作為一個String
和循環,直到該字符串表示int
:
int intScore;
String score;
boolean gotInt = false;
while (!gotInt) {
score = scan.next();
try {
intScore = Integer.valueOf(score);
gotInt = true;
} catch (NumberFormatException e) {
// output some warning
}
}
您是否考慮過使用JOptionPane從用戶那里獲取輸入? 它能夠顯示一個帶有文本字段以及“確定”和“取消”按鈕的小窗口,非常適合您的需求。
這是JOptionPane#showInputDialog的文檔:
static String showInputDialog(Component parentComponent, Object message, String title, int messageType)
顯示一個對話框,該對話框請求以parentComponent為父級的用戶輸入,該對話框具有標題標題和消息類型messageType。
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