CODEWITHSUNDEEP
javaexception
MrGuerino
MrGuerino

Reputation: 11

Understanding Java Exception Handling: Simple Try Catch blocks

I'm trying to learn Java Exception handling. I wrote the following code:

import java.util.*;
public class Problem1
{
    static Scanner length = new Scanner(System.in);
    public static void main(String[] args)
    {
            double x;
            double y;

            System.out.println("Input a length in Feet and than Inches.");

            x = length.nextDouble();
            y = length.nextDouble();

            try
            {
                    System.out.println("Feet - Inches:" + x * 12);
                    System.out.println("Inches - Centimeters:" + y * 2.14);
            }

            catch (InputMismatchException imeRef)
            {
                    System.out.println("Do not use letters" + imeRef.toString());
            }
    }
}

The program simply converts inputs in Feet and Inches to just Inches. I try to break it by giving it an input of:

-1
e

The program breaks but I'm not properly catching and handling the exception. Any ideas what I'm doing wrong?

Thanks

Upvotes: 0

Views: 251

Answers (4)

Blake Caldwell
Blake Caldwell

Reputation: 311

A catch statement only catches exceptions that are thrown in its corresponding try block.

This is what you want. This prompts the user for each question, one at a time, and resets and asks again on bad input. Note the length.next() in the catch - that's needed to avoid an infinite loop - you have to advance past that bad token.

while (true) {
    try {
        System.out.println("Input a length in feet");
        double x = length.nextDouble();

        System.out.println("Input a length in inches");
        double y = length.nextDouble();

        System.out.println("Feet - Inches:" + x * 12);
        System.out.println("Inches - Centimeters:" + y * 2.14);

        break;
    }

    catch (InputMismatchException imeRef) {
        System.out.println("Do not use letters" + imeRef.toString());

        // need to purge the bad token
        length.next();
    }
}

Upvotes: 1

Mengjun
Mengjun

Reputation: 3197

You do not catch exception is because the exception is thrown when calling length.nextDouble() for variable x and y.

  x = length.nextDouble();
  y = length.nextDouble();

But You do not put them in try - catch code. Put the above 2 line code to try - catch, you will catch the exception.

Upvotes: 1

MD Sayem Ahmed
MD Sayem Ahmed

Reputation: 29166

Put the following two lines - 

 x = length.nextDouble();
 y = length.nextDouble();

inside your try block - 

try {
    x = length.nextDouble();
    y = length.nextDouble();

    System.out.println("Feet - Inches:" + x * 12);
    System.out.println("Inches - Centimeters:" + y * 2.14);
}
catch (InputMismatchException imeRef) {
    System.out.println("Do not use letters" + imeRef.toString());
}

A catch block only catches the matching exceptions thrown by the statements inside of its corresponding try block.

Upvotes: 1

Rahul
Rahul

Reputation: 45060

You need to move the 2 input statements which read the input from the user into the try block. The error will be thrown only when the input is read and to handle that in the catch, these statements need to be in the try block because the catch will handle only the exceptions thrown in its corresponding try block.

try {
    x = length.nextDouble(); // moved inside try
    y = length.nextDouble(); // moved inside try
    System.out.println("Feet - Inches:" + x * 12);
    System.out.println("Inches - Centimeters:" + y * 2.14);
}

Upvotes: 2

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