Java：Do-While循环中的Try-Catch语句

Question

I am trying to execute a bit of code that scans for a user input value. This action is contained in a custom method I wrote, named getTriangleDim(); the method reads in the users int value, makes sure it is within a certain range, and then returns the int value that was entered. The method works great and I have no issues with it.

The problem arises when I enter a non-int value for my getTriangleDim() method. It gives me an InputMismatchException error. I have written a try-catch statement into a do-while loop to attempt to fix this issue. But this is the first time I have ever used a try-catch statement, and I am apparently missing something.

Here is the code for the try-catch statement nested within the do-while loop:

//loop to scan for triangle dimension
        boolean bError = true;
        int triangle;

        do{
            try {
                triangle = getTriangleDim();
                bError=false;
                }
            catch (Exception e){
                System.out.println("You did not enter an integer, please enter an integer value");
                triangle = getTriangleDim();

                }
        }while (bError);

if i test it by entering a char value in place of the int, it actually catches the error once, and then prints my "you did not....." statement. But if I re-enter another non-int number, I get a runtime error again that says.......you guessed it........ InputMismatchException error.

The code for my method is here:

//method for scanning triangle dimensions from keyboard
    public static int getTriangleDim(){
        int triangle = 0;
        Scanner keyboard = new Scanner(System.in);
        do{
        System.out.print("Enter a non-zero integer length (+/-1 - +/-16): ");
        triangle = keyboard.nextInt();
        if((!(triangle <= 16 && triangle >= 1))&&(!(triangle >= -16 && triangle <= -1)))
            System.out.println("Inpute value outside of range");
        }while((!(triangle <= 16 && triangle >= 1))&&(!(triangle >= -16 && triangle <= -1)));
        return triangle;
    }

I need the Do-While loop to continue, but I keep getting these errors.

Answer 1

There's no need to ask for input in the catch block. You're already in a loop, so you can catch the exception, tell the user to give you valid input, and then you don't have to do anything else--you'll loop back around to the beginning.

do{
    try {
        triangle = getTriangleDim();
        bError=false;
    } catch (Exception e){
        System.out.println("You did not enter an integer, please enter an integer value");
        // Don't do anything else in here: we will loop back to the beginning again and get new input!
    }
}while (bError);

---

As a side note (and as you've noticed), your code won't currently compile if you try to use triangle outside of that try block, because "triangle might not have been initialized" . This is due to the fact that the compiler cannot determine at compile-time what your program will do at run-time : that is, the compiler cannot see that triangle will always be initialized within that loop. So your variable declaration ought to also set triangle to some default value. 0 is the normal default for int , but use whatever makes sense in your program (it looks like 0 is fine, based on your getTriangleDim code).

int triangle = 0;
do { // etc.

This way you can "promise" the compiler that triangle will have a value by the time you leave the loop, and you'll be able to use it elsewhere.