Thread: Try Catch Problems

Modified that last code a bit. I've got two problems. One, I don't know how to continue the loop so that when the user repeatedly enters the wrong input, it keeps asking again and again. My code just tells the user one time that they have entered the wrong input, then it will accept the second input even though it was wrong. I want it to continue looping until the right input has been entered.
My second question is if I wanted to add another input in, say an int instead of a double, how would I implement that into my try catch? So, I would have my original system.out.print "Enter a decimal number: " and then I would have another system.out.print asking the user to "Enter an integer: " after they input a decimal number. I want the exception phrases of the integer input to be the same as the decimal input. Example, "Invalid decimal number. Please enter a positive number." and for the integer input, "Invalid integer. Please enter a positive number."

import java.util.Scanner;
 
public class decimalNumber {
	public static void main(String[] args) {
		Scanner Input = new Scanner(System.in);
 
		String dec = null;
		double x = 0;
		int i = 0;
 
 
		boolean valid = true;
 
		System.out.println("Enter a decimal number: ");
 
			try {
				dec = Input.next();
				double i1 = Double.parseDouble(dec);
 
				if (i1 <= 0) {
					System.out.println("Invalid decimal number. Please enter a positive number.");
					dec = Input.next();
 
				}
				else  {
					System.out.println();
				}
 
			}
			catch (Exception e) {
				System.out.println("Invalid value. Must be a decimal number.");
				dec = Input.next();
			}
			System.out.println("You entered the decimal number " + dec);
 
	}
 
}

Originally Posted by Norm

Use the continue statement.

Use a separate try catch if you are asking for new data.

So if I had a string input, an integer input, and a double input, I would need to make 3 separate try catch statements for each one? Also, I read up a little on the continue statement, and when I tried putting it in my code, it gave an error saying I can't have it outside a loop. Even though it was in my if loop inside my try catch statement.

I modified my code again. This time I inserted an integer input. My code does not work as it should though. This is an example of the output for this code.
Enter a decimal number:
8.3
Invalid decimal number. Please enter a positive number. //why is it an error?
hi //reads in the wrong input
Enter an integer:
-1938
Invalid Integer value. Please enter a positive number. //this seems to be right
hi //again reads in the wrong input
You entered the decimal number hi and an integer number hi //output is wrong.

import java.util.Scanner;
 
public class bodyMassIndex {
	public static void main(String[] args) {
		Scanner Input = new Scanner(System.in);
 
		String integ = null;
		String dec = null;
		int i = 0;
		boolean valid = true;
 
		System.out.println("Enter a decimal number: ");
		do {
			try {
				dec = Input.next();
				double x1 = Double.parseDouble(dec);
 
				if (i<=0) {
					System.out.println("Invalid decimal number. Please enter a positive number.");
					dec = Input.next();
				}
				else  {
					System.out.println();
					valid = true;
				}
 
			}
			catch (Exception e) {
				System.out.println("Invalid value. Must be a decimal number.");
				dec = Input.next();
			}
 
			System.out.println("Enter an integer: ");
 
			try {
				integ = Input.next();
				double i1 = Integer.parseInt(integ);
 
				if (i1 <= 0) {
					System.out.println("Invalid Integer value. Please enter a positive number.");
					integ = Input.next();
 
				}
				else  {
					System.out.println();
				}
 
			}
			catch (Exception e) {
				System.out.println("Invalid Integer value. Must be a whole number.");
				dec = Input.next();
			}
			System.out.println("You entered the decimal number " + dec + " and an integer number " + integ);
		}while(valid);
	}
 
}

Hello Nuggets!
You have defined and initialized variable i (i = 0) which never changes its value.
In your first try...catch block you have:

		if (i<=0) {
			System.out.println("Invalid decimal number. Please enter a positive number.");
			dec = Input.next();
 
                }

Therefore the print statement will always execute since i is always 0. Maybe you want to test your

double x1 = Double.parseDouble(dec);

in your if statement.
And also your boolean variable valid should change its value to false at some time, otherwise your loop will be infinite.
Hope it helps.

Modified the code again. Everything seems to be working except I need it to keep checking whether the input is correct or not. It throws the exception once, then it will accept it the second time an "Invalid" message appears. For example,

Enter a decimal number:
lll
Invalid value. Must be a decimal number.
-19382
Enter an integer:
-83
Invalid Integer value. Please enter a positive number.
hii
You entered the decimal number -19382 and an integer number hii //see it keeps accepting the wrong input
How would I throw an exception every time there is a wrong input instead of just once?

import java.util.Scanner;
 
public class bodyMassIndex {
 
	public static void main(String[] args) {
		Scanner Input = new Scanner(System.in);
 
		String integ = null;
		String dec = null;
		boolean valid = true;
 
		System.out.println("Enter a decimal number: ");
 
	 do {
			try {
				dec = Input.next();
				double x1 = Double.parseDouble(dec);
 
 
				if (x1<=0) {
					System.out.println("Invalid decimal number. Please enter a positive number.");
					valid = false;
					dec = Input.next();
				}
				else  {
					System.out.println();
					valid = true;
				}
 
			}
			catch (Exception e) {
				System.out.println("Invalid value. Must be a decimal number.");
				valid = false;
				dec = Input.next();
			}
 
			System.out.println("Enter an integer: ");
 
			try {
				integ = Input.next();
				double i1 = Integer.parseInt(integ);
 
				if (i1 <= 0) {
					System.out.println("Invalid Integer value. Please enter a positive number.");
					valid = false;
					integ = Input.next();
 
				}
				else  {
					System.out.println();
				}
 
			}
			catch (Exception e) {
				System.out.println("Invalid Integer value. Must be a number.");
				valid = false;
				dec = Input.next();
			}
			System.out.println("You entered the decimal number " + dec + " and an integer number " + integ);
		} while(!valid);
	}
}

Modified code again. This time I put a do loop around each try catch block. Now, it does repeat the instances asking the user to input the right code over and over. But I must type the input twice for it to read. Why is that? Example of output:

Enter a decimal number:
-29
Invalid decimal number. Please enter a positive number.
lala // why did it ignore this input?
lala // had to enter it twice for the program to read it.
Invalid value. Must be a decimal number.

import java.util.Scanner;
 
public class bodyMassIndex {
 
	public static void main(String[] args) {
		Scanner Input = new Scanner(System.in);
 
		String dece;
		String integ = null;
		String dec = null;
		boolean valid = true;
 
		System.out.println("Enter a decimal number: ");
 
 
		do {
			try {
				dec = Input.next();
				double x1 = Double.parseDouble(dec);
 
 
				if (x1<=0) {
					System.out.println("Invalid decimal number. Please enter a positive number.");
					valid = false;
					dec = Input.next();
				}
				else  {
					System.out.println();
					valid = true;
 
				}
 
		}
			catch (Exception e) {
				System.out.println("Invalid value. Must be a decimal number.");
				valid = false;
				dec = Input.next();
			}
		}while(valid == false);
 
			System.out.println("Enter an integer: ");
 
		do {
			try {
				integ = Input.next();
				double i1 = Integer.parseInt(integ);
 
				if (i1 <= 0) {
					System.out.println("Invalid Integer value. Please enter a positive number.");
					valid = false;
					integ = Input.next();
 
				}
				else  {
					System.out.println();
				}
 
			}
			catch (Exception e) {
				System.out.println("Invalid Integer value. Must be a number.");
				valid = false;
				dec = Input.next();
			}
			System.out.println("You entered the decimal number " + dec + " and an integer number " + integ);
 
		} while(valid == false);
	}
 
}

The reason it asks twice is because your loop contains dec = input.next() twice. The only difference being that the second time it is not parsed and therefore not throwing an exception. I have looked through your different modifications and I must say I liked the first one most. Granted it did not work, it was almost there. I went ahead and made a project on my comp and got the code working nicely, I hate typing out explanations so I will use some sudocode (non syntax critical code-like text) to maybe help a bit.

class decimalNumber {
	main(String[] args) {
		Scanner Input = new Scanner;
 
		double decimal = 0;
		int integer = 0;
                boolean valid = false;
 
		do {
			try {
                                ask user to enter a decimal
				dec = input.nextDouble()
				if dec <= 0 then
                                    tell user they screwed up
				else
                                    they didn't screw up
			            valid = true
			}
			catch (e) {
				tell user they really screwed up
				Input.next()  // this is the kind of important part, makes the Scanner move on to the next input else it will not turn out so nice.
			}
		}while(!valid)

Hope this can help.


- Michael

The problem is when I change decimal to a double instead of a string, the program crashes when I enter a string as an input. For some reason it won't catch the error, just crashes the program. My catch statement remained the same. Everything else is fine though.

Nvm guys, I got the code working. I wasn't posting my real code btw. This program is for class and I didn't want to get in trouble if the wrong person saw it. My program works properly now. Much thanks to everyone who helped me in this thread! I will give thanks to everyone who contributed.

I'll attempt to piggyback on this thread with a quick catch question in case someone checks in.

My catch(InputMismatchException e) will catch decimal inputs. I'd like the decimals to pass through. Is there a way to avoid that?

Well, the loop looks like this. I'm trying to catch negative numbers and non-numbers, but it catches decimals like 5.5.

do{
 
		try {
 
			error = false;
 
 
			System.out.println("Enter a positive number");
			number = console.nextInt();
 
			while (number<= 0)
			{
				System.out.println("Invalid number value. Must be positive.");
				number = console.nextInt();
			}	
 
			}
 
		catch(InputMismatchException e)
		{
			error = true;
			console.nextLine();
			System.out.println("Invalid number value.  Must be a decimal number.");
 
		}
 
	} while(error);

I knew I was missing something stupid. Thanks a ton!