Java Program - Email address verification using Strings and RegEx

Question

The problem statement goes like this:

We need to create a String data type called emailId

The email ID has to be set using appropriate setter methods.

The validation rules for the email ID check have to be implemented in the main().

Conditions are:

1. Overall length of the email ID must be >3 and <20.

2. The emailId must include "@" followed by a minimum of 1 and maximum of 2 "." characters.

3. The substring before "@" must contain a combination of Upper Case, Lower Case and "_"(underscore) symbols.

4. The first letter of the email Id must be in Upper Case.

If all the above conditions are valid, it should display "Email ID is valid" or else, it should display an appropriate error message

This is my code:

public class EmailCheck {

String emailId;
public void setEmailId(String emailId){
    this.emailId=emailId;
}
public String getEmailId(){
    return emailId;
}
public static void main(String[] args) {
    EmailCheck em = new EmailCheck();
    em.setEmailId("[email protected]");
    String email = em.getEmailId();
    int length = email.length();
    boolean flag1 = false;
    boolean flag2 = false;
    boolean flag3 = false;
    boolean flag4 = false;
    boolean flag5 = false;
    boolean flag6 = false;
    boolean flag7 = false;
    int count = 0;


    //Condition 1 
    if((length>3 && length<20)== true)
        flag1 = true;
    else 
        flag1 = false;

    //Condition 2
        int temp = email.length();
        if(email.contains("@")){
            flag2=true;
            int a=email.indexOf("@");
             for(int i=a;i<temp;i++){
        if(email.charAt(i)=='.'){
        flag3=true; 
        count=count+1;
        }
        }
        if(count<1||count>2){
        flag4=false;
        }
        else{
        flag4=true;
        }
        }
        else{
        flag2 =false;
        System.out.println("No @ symbol present");
        }


    //Condition 3
    if(email.matches("[A-Z a-z _]+@.*")) //Unable to get the right RegEx here!
        flag5 = true;
    else
        flag5 = false;

    //Condition4
    if(Character.isUpperCase(email.charAt(0))==true)
            flag6 = true;
    else
        flag6=false;

    if(flag1==true && flag2==true && flag3==true && flag4==true && flag5==true &&flag6==true)
        System.out.println("Email ID is valid");
    else{
        if(flag1==false)
            System.out.println("Inavlid length of Email ID");
        if(flag2==false||flag3==false||flag4==false)
            System.out.println("Invalid Position of Special Characters");
        if(flag5==false)
            System.out.println("Invalid combination for username");
        if(flag6==false)
            System.out.println("Invalid case of first letter");
    }


}
}

I'm not sure of the condition #2(the logic?) and condition #3(the RegExp part). A few of the test cases seem correct, the rest of them are wrong(owing to faulty logic in #2 and esp #3, I think.)

Please, tell me what changes have to be done here to get the right output. Thanks!

Solution

If you insist on using regex you can use this but without validating properly you could be in for all kinds of trouble

static Pattern emailPattern = Pattern.compile("[a-zA-Z0-9[!#$%&'()*+,/\-_\.\"]]+@[a-zA-Z0-9[!#$%&'()*+,/\-_\"]]+\.[a-zA-Z0-9[!#$%&'()*+,/\-_\"\.]]+");

public static boolean isValidEmail(String email) {

    Matcher m = emailPattern.matcher(email); return !m.matches();

}

Or alternatively you could use

public static boolean isValidEmailAddress(String email) {
   boolean result = true;
   try {
      InternetAddress emailAddr = new InternetAddress(email);
      emailAddr.validate();
   } catch (AddressException ex) {
      result = false;
   }
   return result;
}

Which is a core java utility which would be better...

Note that neither of these will guarentee an address is actually valid, just that it is correctly formed and so hypothetically could exist

String email_regex = "[A-Z]+[a-zA-Z_]+@\b([a-zA-Z]+.){2}\b?.[a-zA-Z]+";
String testString = "[email protected]";
Boolean b = testString.matches(email_regex);
System.out.println("String: " + testString + " :Valid = " + b);

will check for the last three constraints which you can then combine with

string.length()>3 && string.length()<20

Comments

[SLaks]

Every one of your validation rules is wrong. Don't do this.

[Maroun]

Side note: if((length>3 && length<20)== true) should be if(length>3 && length<20)

[user2377778]

@Slaks Can you please suggest what I should improve on?

[Kyle]

Wrong is subjective. That could be right under certain circumstances. Sounds like class work though

[SLaks]

Get rid of them all. The rules for valid email addresses are extremely complicated; you should use commons.apache.org/proper/commons-validator/apidocs/org/apac‌​he/…

[Brian Roach]

stackoverflow.com/questions/201323/…

[SLaks]

@Kyle: I can't think of any sane circumstances in which any of the rules would be right.

[user2377778]

@SLaks :( Oh! I will look into it. I'm just a beginner at Java, coding this for a java 101 class, so we've been provided with a few rules to get the grip of programming, that's all.

[user2377778]

@Kyle : Yes, this is classwork. Basics of Java Programming.

[aran]

this code is so wrong my JVM is crying

[Kyle]

[A-Z][a-zA-Z_]*(?<=_)(?<=[A-Z])(?<=[a-z])@.{1,2}(?<=.{4,19}) ill throw out a one liner.

[user2377778]

@Kyle All the 4 conditions need not be in the same reg-expression. Just the RegExp for Condition #3 would suffice.

[user2377778]

Thank you so much @thegrinner

[Joseph]

Maybe you could update your answer with the last example from here howtodoinjava.com/regex/java-regex-validate-email-address otherwise good explanation you gave there.