Check if string contains an @ symbol or if the string is null

Question

Basically, I have a form where people can enter stuff in, and there is one part where they input an email address. Sometimes, people just put in their name and don't put an actual email address. Sometimes they do not fill it out at all.

Is there any easy way to check to see if the string has an @ symbol in it and check to see if its Null?

Any help is appreciated

Actually it should be the other way round!!: `str != null && str.contains("@")` — jokster, Jan 11 '19 at 16:04
@achAmháin if str is null, then this will throw NPE.. check for null first. — kscherrer, Jan 11 '19 at 16:04
Why would you need java to do a front end validation? I think you are better off looking for a JavaScript answer. — Nicholas K, Jan 11 '19 at 16:16

score 1 · Accepted Answer · answered Jan 11 '19 at 16:06

1

Use an AND boolean operator.

str != null && str.contains("@")

We first check the string is not null, then check that it contains '@'. Note: The reason that the null check is first is so that we do not attempt to access the string if it is null.

answered Jan 11 '19 at 16:06

James Conway

339
3
20

This answer is what I needed - how do I mark it as a verified answer? – xearow Jan 11 '19 at 16:25
Click the grey tick and it will become green. – James Conway Jan 11 '19 at 16:32

score 0 · Answer 2 · answered Jan 11 '19 at 16:05

0

String s = "email@email.it";
    if(s!= null && !s.isEmpty() && s.contains("@") ) {
        System.out.println("ok");
    }
    else System.out.println("ko");
}

answered Jan 11 '19 at 16:05

Matteo Tomai

174
9

1

`!s.isEmpty()` is not needed. When s contains "@", it is never empty – kscherrer Jan 11 '19 at 16:06
yes, but he want to check if it's null, so I thought to check even if it was empty – Matteo Tomai Jan 11 '19 at 16:08

score 0 · Answer 3 · edited Jun 20 '20 at 09:12

The String class contains a contains method to check the @ symbol, and you can simply check for null with a != null call:

public static void main(String[] args) {
    String a = "should be false";
    String b = "should be @true";
    String c = null;
    System.out.println(checkString(a));
    System.out.println(checkString(b));
    System.out.println(checkString(c));
}

static boolean checkString(String str) {
    return str != null && str.contains("@");
}

Output:

false

true

false

score 0 · Answer 4 · answered Jan 11 '19 at 16:19

Here is some really simple code to achieve this:

String ourString = "example@emailIsCool.com";
if(/* Check if our string is null: */ ourString != null &&
   /* Check if our string is empty: */ !ourString.isEmpty() &&
   /* Check if our string contains "@": */ ourString.contains("@")) {
    System.out.println("String Fits the Requirements");
} else {
    System.out.println("String Does Not Fit the Requirements");
}

For future reference, this is extremely broad for Stack Overflow, and you should try checking the javadoc before you make a post asking for the answer. For example, here is the javadoc for the String class: https://docs.oracle.com/javase/7/docs/api/java/lang/String.html

Javadocs provided by Oracle detail every method and attribute for all of the classes included in the standard java library. Here is a link to the javadoc homepage for Java 7. https://docs.oracle.com/javase/7/docs/api/overview-summary.html

Oh wow, I did not know that was a thing. I'll have to get familiar with looking through that. — xearow, Jan 11 '19 at 16:25

score 0 · Answer 5 · answered Jan 11 '19 at 16:31

I think use Optional is the best way to do this.

Codes like this:

String nullEmail = null;
System.out.println(Optional.ofNullable(nullEmail).filter(s -> s.contains("@")).isPresent());

String rightEmail = "478309639@11.com";
System.out.println(Optional.ofNullable(rightEmail).filter(s -> s.contains("@")).isPresent());

String wrongEmail = "chentong";
System.out.println(Optional.ofNullable(wrongEmail).filter(s -> s.contains("@")).isPresent());

The output is:

false
true
false

Check if string contains an @ symbol or if the string is null

5 Answers5