Simple Java Email Harvester Program

[singular]

Hey guys, I am learning Java and am attempting a project from a book, but I have run into a problem. I don't have an issue when it comes to harvesting an address that has whitespace on both sides. My issues come when a) the input doesn't contain whitespace on either side of an address and b) the input doesn't have an address at all (my program recognizes an address as containing an @ and whitespace on either side.

How do I get the program to run without error considering my two issues and simply print an "@" if there is no email address present with using only the the methods I already have in my program (I can't use looping or conditional structures)?

Here is my code thus far:

import java.util.*;

public class Harvester
{
public static void main(String[] args)
{
// Title of program
System.out.println("Email Address Harvester");

// Set up input stream
Scanner scan = new Scanner(System.in);

// Prompt input from user
System.out.print("Input line: ");

// Scan input
String input = scan.nextLine();

// Set j to index of the first "@" in input
String searchString1 = "@";
int j = input.indexOf(searchString1, 0);

// Set i to minimal index in input such that all characters in positions i through j are nonblank
String searchString2 = " ";
int i = input.lastIndexOf(searchString2, j);

// Set k to maximal index in input such that all characters in positions j through k are nonblank
int k = input.indexOf(searchString2, j);

// Set email address to the substring of input with indices i through k
String emailAddress = input.substring(i, k);

// Print email address.
System.out.println("Extracted email address: " + emailAddress);
}
}

 

[chroot]

Design it the right way. Use a regular expression.

- Warren

 

[singular]

Design it the right way. Use a regular expression.

- Warren

Ok, but if I were to stay within the bounds of using only string operations and methods, how do you suggest I fix the problem of when the input doesn't contain an email address? How would I get the program to print only an @ under this condition?

 

[CaptainQuasar]

Really, you should just use a regular expression. I'm not familiar with the Java classes for doing that but there's usually a .Success boolean property that simply tells you whether there was a match or not. If you want to reinvent the wheel, unless you give a good reason to you may not find lots of help to be forthcoming.

⚛​

 

[chroot]

Ok, but if I were to stay within the bounds of using only string operations and methods, how do you suggest I fix the problem of when the input doesn't contain an email address? How would I get the program to print only an @ under this condition?

You're using indexOf() to find an @ sign. If there is no @ sign, indexOf() will return -1. You can check to see that the result is -1, and do something about it. As it stands, your program doesn't check it, and goes on to blindly use it in the next line of code, which then throws the exception.

- Warren

 

[singular]

You're using indexOf() to find an @ sign. If there is no @ sign, indexOf() will return -1. You can check to see that the result is -1, and do something about it. As it stands, your program doesn't check it, and goes on to blindly use it in the next line of code, which then throws the exception.

- Warren

Thanks for your help. I am going to forgo trying to find another solution (there doesn't seem to be one) and use an if-else statement to check the value like you suggested.

 

[DualCortex]

Try to read this "tutorial" entirely to get a hold of how regular expressions work and how to apply them:
http://www.regular-expressions.info/tutorial.html

In fact, right in the first page they show you an example of an email pattern

\b[A-Z0-9._%+-]+@[A-Z0-9.-]+\.[A-Z]{2,4}\b