java - JAVA中try-catch的死循环

Question

所以我想做的是让用户在矩阵中输入一个有效的坐标，即大于-1的INT，

Scanner scanner = new Scanner (System.in);
int coordinates[] = new int[2];
coordinates[0]=-1;  
coordinates[1]=-1;
boolean check = true;
while (((coordinates[0]<0)||(coordinates[0]>R))  && check) {
    System.out.print("Please enter a valid row number:\t");
    try { 
        coordinates[0]=scanner.nextInt(); 
        break; 
    }
    catch (InputMismatchException e) {
    }
}
while (((coordinates[1]<0)||(coordinates[1]>C)) && check) {
    System.out.print("Please enter a valid col number:\t");
    try { 
        coordinates[1]=scanner.nextInt(); 
        break; 
    }
    catch (InputMismatchException e) {
    }       
}

问题是输入无效输入后会无限循环int R 是行的大小int C 是列的大小

Answer 1

您的问题是您没有处理您捕获的错误。如果您为 nextInt() 方法提供了错误的数字格式，则将抛出 InputMismatchException。然后，因为 catch 不执行任何操作，循环将继续(从头开始)，并且扫描器将读取相同的错误值，依此类推...

所以代替这个:

catch (InputMismatchException e) {
}  

试试这个:

catch (InputMismatchException e) {
    System.out.println("Wrong number entered.");
    scanner.nextLine();
}   

这样，您将强制扫描仪移过最后一个不正确的输入。

编辑:

你的循环也被破坏了，因为你在读取输入后break。在这种情况下，如果您输入负数，您也会中断并且不会检查循环条件。删除 break 语句，它将按预期工作:

while (((coordinates[0]<0)||(coordinates[0]>R))  && check) {
    System.out.print("Please enter a valid row number:\t");
    try { 
        coordinates[0]=scanner.nextInt(); 
    }
    catch (InputMismatchException e) {
        System.out.println("That's not a valid number.");
        scanner.nextLine();
    }
}

编辑2:

public static void main(final String args[])
{
    int maxRowsNumber = 10;
    int maxColsNumber = 10;
    Scanner scanner = new Scanner (System.in);
    int coordinates[] = new int[2];
    coordinates[0]=-1;  
    coordinates[1]=-1;
    boolean check = true;
    while (((coordinates[0]<0)||(coordinates[0]>maxRowsNumber))  && check) {
        System.out.print("Please enter a valid row number:\t");
        try { 
            coordinates[0]=scanner.nextInt(); 
        }
        catch (InputMismatchException e) {
            System.out.println("That's not a valid number.");
            scanner.nextLine();
        }
    }
    while (((coordinates[1]<0)||(coordinates[1]>maxColsNumber)) && check) {
        System.out.print("Please enter a valid col number:\t");
        try { 
            coordinates[1]=scanner.nextInt(); 
        }
        catch (InputMismatchException e) {
            System.out.println("That's not a valid number.");
            scanner.nextLine();
        }       
    }
    System.out.println("Inserted RowsNumber: " + coordinates[0]);
    System.out.println("Inserted RowsNumber: " + coordinates[1]);
}

输出:

Please enter a valid row number:    11
Please enter a valid row number:    22
Please enter a valid row number:    10
Please enter a valid col number:    11
Please enter a valid col number:    2
Inserted RowsNumber: 10
Inserted RowsNumber: 2