error handling

[cool dude]

i can catch errors but the problem i'm having is when i catch them the program just finishes. i tried putting all my code in a loop however once the error is caught it will repeat the very first question in the loop because it will just restart the loop. how can i get it to keep reasking for a valid input?

[wtd]

Show us the code you have.

[cool dude]

wtd wrote:

Show us the code you have.

well the code is kinda long so i don't think anyone wants to be looking through all the code. so i'll make a very small sample program right now so you guys can show me how this can be done so then i can implement the same thing into my program.

[cool dude]

Here is the sample program i just finished making. This is not my program its just an example to learn how to keep reasking the same question until valid input is received.

code:

import java.io.*; public class Sample {    public static void main(String[] args)    {              int num1, num2;                try                {                       BufferedReader myInput = new BufferedReader(new InputStreamReader(System.in));                       //asks for input from user - 2 numbers and operation                 System.out.println("Enter first number");                 num1 = Integer.parseInt(myInput.readLine());                 System.out.println("Enter second number");                 num2 = Integer.parseInt(myInput.readLine());                }                catch (NumberFormatException nfe) {                 System.out.println("can't convert: ");         }         catch (IOException f) {                 System.out.println("error reading input");         }             } }

[HellblazerX]

Why not use a flag? When your program gets the data it wants, just use the flag to exit out of the loop. Otherwise, just stay in the loop if the wrong data is given.

[wtd]

My suggestion would be to use "break" and "continue."

If break is encountered in a loop, it will cause control flow to exit that loop.

If continue is encountered, it will cause the loop to skip straight to the next iteration.

If you have a parsing operation, and then directly afterwards a "break" statement, and the whole thing is wrapped up in a try...catch construct, then if an exception is encountered parsing the string, control flow will skip straight to the appropriate "catch" block, bypassing the "break" entirely.

A further note: You have essentially the same operation repeated twice. You want to prompt the user repeatedly for a number until the input they give you is a valid number. You also wish to display an error message when bad input is given.

This is best factored out into a method which you could call twice.

[cool dude]

HellblazerX wrote:

Why not use a flag? When your program gets the data it wants, just use the flag to exit out of the loop. Otherwise, just stay in the loop if the wrong data is given.

that is exactly wat i did but the problem with that is that when the wrong data is given it will stay in the loop but it will cycle through the start of the loop so it will ask the very first question. however what if the wrong input is asked on the second question. then it will repeat the first question which won't make sense.

wtd i'm a little confused on what you said. care to elaborate

Thanks

[cool dude]

i just checked out your tutorial. Thank you for making one! i do appreciate it. i am kinda confused on things you did. for example:

Quote:

class UtilityClass {
public static int getInt(Scanner input, String prompt) {
int result = 0;

while (true) {
try {
System.out.print(prompt + " ");
result = input.nextInt();
break;
}
catch (InputMismatchException e) {
}
}

return result;
}

public static int getInt(Scanner input, String prompt, String errorMessage) {
int result = 0;

while (true) {
try {
System.out.print(prompt + " ");
result = input.nextInt();
break;
}
catch (InputMismatchException e) {
System.out.println(errorMessage);
}
}

return result;
}
}

These are constructors i'm assuming. however i don't understand why you make a loop and then you break to get out of the loop?
Also you made two constructors one which will go into if there is no error and one will go into if there is an error (i think). why can't you just assume there is an error and just make one constructor. if no error is found then the program will just continue so why is there two constructors?

Also does this mean i will have to make a class with constructors and all that work just to catch an error and reask the question? i don't really want to sound lazy but thats a lot of work just to catch an error which only motivates me to throw exceptions. Is there another way?[/code]

[cool dude]

wtd wrote:

My suggestion would be to use "break" and "continue."

If break is encountered in a loop, it will cause control flow to exit that loop.

If continue is encountered, it will cause the loop to skip straight to the next iteration.

If you have a parsing operation, and then directly afterwards a "break" statement, and the whole thing is wrapped up in a try...catch construct, then if an exception is encountered parsing the string, control flow will skip straight to the appropriate "catch" block, bypassing the "break" entirely.

A further note: You have essentially the same operation repeated twice. You want to prompt the user repeatedly for a number until the input they give you is a valid number. You also wish to display an error message when bad input is given.

This is best factored out into a method which you could call twice.

by what i understood you meant something like this:

code:

import java.io.*; public class Sample {    public static void main(String[] args)    {        int num1, num2;        while(true)        {                try                {                   BufferedReader myInput = new BufferedReader(new InputStreamReader(System.in));                   //asks for input from user - 2 numbers and operation                    System.out.println("Enter first number");                    num1 = Integer.parseInt(myInput.readLine());                    System.out.println("Enter second number");                    num2 = Integer.parseInt(myInput.readLine());                    break;                }                catch (NumberFormatException nfe) {                    System.out.println("can't convert: ");                    continue;                }                catch (IOException f) {                  System.out.println("error reading input");                  continue;                }               }    } }

This will work if the error is on the first input however, if the error is on the second input then it will reask the first question and then the second question.

[wtd]

cool dude wrote:

These are constructors i'm assuming.

In UtilityClass, they are not constructors. They are simply static methods. You would call them as "UtilityClass.getInt(...)".

[wtd]

cool dude wrote:

wtd wrote:

My suggestion would be to use "break" and "continue."

If break is encountered in a loop, it will cause control flow to exit that loop.

If continue is encountered, it will cause the loop to skip straight to the next iteration.

If you have a parsing operation, and then directly afterwards a "break" statement, and the whole thing is wrapped up in a try...catch construct, then if an exception is encountered parsing the string, control flow will skip straight to the appropriate "catch" block, bypassing the "break" entirely.

A further note: You have essentially the same operation repeated twice. You want to prompt the user repeatedly for a number until the input they give you is a valid number. You also wish to display an error message when bad input is given.

This is best factored out into a method which you could call twice.

by what i understood you meant something like this:

code:

import java.io.*; public class Sample {    public static void main(String[] args)    {        int num1, num2;        while(true)        {                try                {                   BufferedReader myInput = new BufferedReader(new InputStreamReader(System.in));                   //asks for input from user - 2 numbers and operation                    System.out.println("Enter first number");                    num1 = Integer.parseInt(myInput.readLine());                    System.out.println("Enter second number");                    num2 = Integer.parseInt(myInput.readLine());                    break;                }                catch (NumberFormatException nfe) {                    System.out.println("can't convert: ");                    continue;                }                catch (IOException f) {                  System.out.println("error reading input");                  continue;                }               }    } }

This will work if the error is on the first input however, if the error is on the second input then it will reask the first question and then the second question.

This is best factored out into a method which you could call twice.