How to re-prompt user after invalid input in java?

Question

Problem:

Well, I need to write a program that will re-prompt the user after invalid input in java. Let’s say my program prompt value from the user and store in a variable. Then it will compare the variable and my desire value. If the value satisfies my condition it should print out directly, and if not it will ask for a re-prompt.
I hope I explained my problem clearly. Now, I am looking for a solution from you guys. Please, find my sample code below and check where I am doing wrong

System.out.println("What is your expected value?\n");
    value = userInput.nextInt();
    if((value > 100) || (value < 1)) {
        System.out.println("ERROR Please enter a valid value");
        System.out.println("");
        System.out.println("Put the value again, please\n");
        value = userInput.nextInt();
    }

Many thanks.

Answer 1

You need to remember that, the if-statement is a boolean type operator. In your case, you had to use a while-loop for getting the re-prompt option. Let’s replace the IF with a while-loop. 

while (true) {
    System.out.println("What is your expected value?\n");
    value = userInput.nextInt();
    if ((value > 100) || (value < 1))
        System.out.println("ERROR! Please enter a valid value\n");
    else
        break;
}

This while break keeps checking the user prompted value and compares with the condition. Once it satisfies the condition it breaks the loop.

Good Day!

Answer 2

You have to know that the if is the Boolean type operator.

Solutions:

 You have to use another loop like while, do-while loop to solve your problem.

Replace if with the while:

System.out.println("What is your age?\n");

age = userInput.nextInt();

while((age > 120) || (age < 1)) {//error message

    System.out.println("ERROR Please enter a valid age");

    System.out.println("");

    System.out.println("What is your age?\n");

    age = userInput.nextInt();

}//end i

If the user enters an invalid character like “E” or anything else which is not a number, then the loop will exit and if the age is less than 1 year or greater than 120 years then it will ask the user again to enter the correct values. The loop will continue to looping until the conditions are met.

Use the do-while loop:

boolean valid;

do {

     System.out.println("What is your age?\n");

     age = userInput.nextInt();

     valid = age > 1 && age < 120;

     if (!valid) {

       System.out.println("ERROR Please enter a valid age");

     }

}while (!valid);

 

To read the user input, it will prompt the user to type her input into the console and will continue to looping until the valid values found.

I hope this will help to solve your problem.