String Comparison

[SJ Carter]

Hi everyone,

I am nearing completion on a program I am writing, but seem to have gone blank with regards to one last method.

I have got a string which contains 7 characters(a combination of letters and numbers). These characters should be stored either in the format 2 letters, 2 numbers, 3 letters or 1 letter, 3 numbers, 3 letters.

The method has to be able to determine whether the characters are stored in either of the above sequences, or it throws an exception. My problem is that I've managed to write code to compare the characters to the first format, but can't seem to get my head round being able to compare the string to both formats, and being able to distinguish between the two formats.

I have tried to use the StringTokenizer but as there is not obvious delimiter I don't know any other way of achieving this.

Any help will be greatly appreciated.

ps. I'm a newbie, so don't be too harsh with me

thanks

[Paul Sturrock]

Have a look at the java.util.regex package. If you are looking for a certain pattern, you can write a regular expression for each and match it against your string.

One quetion, when you say "there is not obvious delimiter" what do you mean by that? Does it mean that your three groups of characters can be delimited by absolutely anything, or that there is more than one delimiter allowed?

[Jason Kretzer]

You could use an if statement based on whether the second character is a letter or number to distinguish between the formats. Look at the Character class and the String charAt() method.

//pseudocode
if(character at position 1 is a letter)
{
    //then process the string for the first format
}
else
{
    //then process the string for the second format
}

Glad I could help with your homework.

[Jason Kretzer]

Also, don't forget to check for a null String or that the String length is long enough before trying to access any characters. Otherwise a NullPointerException or IndexOutOfBoundsExcpetion respectively, will be thrown.

 if(str != null && str.length() == 7) 

[Stan James]

I'd vote for the regular expression solution over the 2nd character solution. The first job of code is to communicate to humans what you meant to do. Being explicit about the two formats is a good thing and would give you full validation to boot.

[Jason Kretzer]

Generally, I would as well. However, since they said this in their original post:

ps. I'm a newbie, so don't be too harsh with me

I gave them a solution that did not require that they learn too much beyond Java i.e. regular expressions.

6 one way , half a dozen another...