[Java] Ignoring Letters

[Androme]

Is there a way to ignore letters when entered into an input that is storing the value as an integer? (if someone accidentally enters letters into the input) If so, a way to repeat the input message if letters were accidentally included?

There's an e.g. ans.equalsIgnoreCase statement but I can't find one for IgnoreLetters... ?

Thanks.

[Androme]

Also, how do you add more than one statement in the 'or' expression?

e.g.

I can do 2 statements so that only if both statements are true:

if (vote_three > vote_one && vote_three > vote_two)


but how would I do e.g. vote_three > vote_one OR vote_three > vote_two in the above statement and in the statement below?


if (zerovoters.equals("yes"))

^^ e.g. for above - if zerovoters == "yes or y" if you see what I mean?


Thanks.

[Phil^]

1) enclose it in a try-catch block, catch the NumberFormatException and make them enter it again if caught.
for instance

         int input = 0;
        boolean valid = false;
        do
        {
            try
            {
                input = Integer.parseInt(javax.swing.JOptionPane.showInputDialog(null,"gimmie a number")); // woo gui input! tho you can do this however you want
            }
            catch (NumberFormatException ex)
            {
                javax.swing.JOptionPane.showMessageDialog(null,"thats not a number");
                continue;
            }
            // if we get here, its valid
            valid = true;
        }
        while ( !valid );

2) use the || , luke!
|| = logical OR
&& = logical AND
putting a ! in front of a parameter makes it check if the inverse is true
for instance : if ( !water.equals("wet") )
would only trigger when water is not wet

if ( vote_three > vote_one || vote_three > vote_two )
if ( zerovoters.equals("yes") || zerovoters.equals("y") )
etc is what you want
it might be better to check to see if the first letter equals y though - as that would catch both cases with one stone

[Ramihyn]

Originally Posted by Phil^

it might be better to check to see if the first letter equals y though - as that would catch both cases with one stone

And also covers "Yeah", "Yay" etc.

/me cries

[Androme]

Thanks guys

[Floi]

has nothing to do with your problem, but:

Originally Posted by Androme2

if (zerovoters.equals("yes"))

is not a good idea

make it:
if ("yes".equals(zerovoters))

alway do it constant.equals(variable) NOT variable.equals(constant)

why?

if the variable is null, u will get an nullpointerexception, other way round it will say its not equal.

gl, Floi

[Phil^]

getting a null pointer exception is a good thing. Sometimes you want to be able to determine if something has gone seriously wrong with user input or otherwise, and catch it.
Its like an added signal - " its not only not equal, its nonexistant. dangerous to use this variable in further code. throw a wobby and demand it be fixed"
For instance, if in the example - when they are not equal it calls the objects .toString() method, it would still throw a null pointer exception but it wouldnt have been caught until that point which could be several objects and methods in, having been copied to numerous other objects as a reference etc etc

[Floi]

Exceptions in gerneral are not a bad thing. And if u handle them - everything is fine.

Just thought in the example above it was just an input that should be checked if its "yes" or not and then thrown away. Of course u need to handle it, if u need the variable later. And the earlier u do, the better.

Just wanted to point out, that he might get in problems, if he does it the way it was posted - and there was no hint for him to put a try-catch around it. (or at least i didnt see it)

[Phil^]

true, it would be much better in a try catch block
Rule number one of user input : the users are stupid. Never underestimate the power of stupidity in large numbers.

[Androme]

Originally Posted by Floi

make it:
if ("yes".equals(zerovoters))
alway do it constant.equals(variable) NOT variable.equals(constant)

if the variable is null, u will get an nullpointerexception, other way round it will say its not equal.

Can't I just make a new public and create my own error message? While I understand your formatting, it's just confusing me.

According to the Sun API, I can make a new public and set my own message if the variable is returned as being null.


public NullPointerException(String s)

Constructs a NullPointerException with the specified detail message.

[Androme]

Btw, is there a way to ignore numbers in an input (only accept letters)?

Would I use the same try and catch principle?

Thanks.

[pablissimo]

Use a regular expression in that instance. Something like ^[\w|\s]*$ maybe but I've done no regex stuff in years so someone else round here'd be better for that.

[Phil^]

or you could use a for loop to break the string down into chars and compare each one using Character.isDigit or Character.isLetter , as defined in http://java.sun.com/j2se/1.3/docs/ap...Character.html
use String.charAt() to get a char from a string
Its not a good idea to create your own exception class which overrules a default one, so dont use the name NullPointerException for one.
A try-catch here wont work unless you create a compare function which throws a custom defined exception like NotALetterException , that you create yourself

[Androme]

thanks

[Androme]

I'm having some problems

       do {
             for (int i=1; i<2; i++)
             {
             	 answer[0] = JOptionPane.showInputDialog(question[0]);
             	 
             	 
             	 
             	 if (answer[0].equalsIgnoreCase("yes"))
				 {
			        answer[2] = JOptionPane.showInputDialog(question[2]);
				 }
				   
				 else if (answer[0].equalsIgnoreCase("no"))
			     {
			       	answer[5] = JOptionPane.showInputDialog(question[5]); 
			     }
			       
			     else
			     {
			     	for (int j=1, j<=3, j++)
			        {
	                     answer[0].charAt(j)
	                     
	                     if (Character.isDigit(answer[0]))
					     {
					     	JOptionPane.showMessageDialog(null, "Number entered.");
					     }
					     
					     else
					     {
					       	JOptionPane.showMessageDialog(null, "You did not enter yes or no.\n\n Please go back and try again."); j--;
					     }
				     
				    }
				 
		          }
		          
		      }
		      		       
		  } while (!answer[0].equalsIgnoreCase("yes") || !answer[0].equalsIgnoreCase("no"));