使用while循环验证布尔输入

Question

I'm doing some Java homework and I can't get this while loop to work correctly.

I've tried to editing the code, but it keeps giving errors.

while(true) {
            System.out.println("Is student a TA? (1: YES 0: NO): ");
                status = inReader.nextInt();
                    if (status == 1) {
                        status1 = true;
                    }
                    else if (status == 0) {
                            status1 = false;
                    }
                    else {
                        System.out.println("Please enter valid entry.");
                    } 
            Graduate grad = new Graduate(studentID, name, major, status1);
            grad.displayStudentData();
                }   
            }
        }
   }

I want the code to loop back if the user inputs anything other than a 0 or 1. It does loop back but the information gets outputted to the console. Which is not what I was hoping it would do.

Answer 1

I'm going to assume that what you are doing with the grad variable is the information you don't want displayed when you get an invalid answer. I'm also assuming you eventually want to exit the loop.

boolean doLoop = true;
Graduate grad = null;

while(doLoop) {
        System.out.println("Is student a TA? (1: YES 0: NO): ");
        status = inReader.nextInt();

        if (status == 1) {
            grad = new Graduate(studentID, name, major, true);
            doLoop  = false;
        }
        else if (status == 0) {
            grad = new Graduate(studentID, name, major, false);
            doLoop  = false;
        }
        else {
            System.out.println("Please enter valid entry.");
        } 

        if (grad != null){
            grad.displayStudentData();
        }
    }
}

Checking for a null allows you to only display something when there's something to display.

Getting rid of the status1 variable reduces the number of variables you need to mentally keep track of. That variable isn't necessary anyway, since there are better ways to deal with validating an input.

Setting the doLoop variable allows you to exit the while when you need to.

Also, the code you posted had a few extra close brackets. It's a good idea to make sure the code you post is either runnable or pseudo-code.

Answer 2

I suggest that you take a step back from writing code and describe the steps in English (or any other written human language). For example, you can write something like this:

while input is invalid
    get input
    check if input is valid
create a Graduate object
display data

This is called "pseudocode". Note how I use indentation similar to how we write code to indicate what steps are repeated in the while loop. This also shows how the last two steps should not be inside the while loop.

If you want to be able to do this for multiple students then there should be another loop around this one. Again, write the steps in words to figure out the exact structure that you need.

Answer 3

Solution :

boolean run = true;
while(run){

    boolean valid = true;
    System.out.println("Is student a TA? (1: YES 0: NO): ");
    status = inReader.nextInt();
    boolean status;
    if (status == 1) {
        status1 = true;
        run = false;
    }
    else if (status == 0) {
        status1 = false;
        run = false;
    }
    else {
        System.out.println("Please enter valid entry.");
        valid = false;
    } 
    if(valid){ //or if(valid == true)
        Graduate grad = new Graduate(studentID, name, major, status1);
        grad.displayStudentData();
    }
}  

Answer 4

What you have going on is that once input that is not 1 or 0 is inputted, you will execute the code in the else block. Then your code will execute

Graduate grad = new Graduate(studentID, name, major, status1);
grad.displayStudentData();

If you didn't want that to be executed, add continue; to the end of the else block.

Answer 5

You say it yourself,

I want the code to loop back if the user inputs anything other than a 0 or 1

so why not put that in the condition?

// initialize with invalid value so we enter the loop at least once
int input = -1;
while (input != 0 && input != 1) {
    System.out.println("Is student a TA? (1: YES 0: NO): ");
    input = inReader.nextInt();
}
// now you're guaranteed to have a 0 or 1 in the input
boolean status = input == 1; // will the true on 1, false on 0
Graduate grad = new Graduate(studentID, name, major, status);
grad.displayStudentData();