How to check a string is not null?

Question

if(string.equals(""))
{

}

How to check if the string is not null?

if(!string.equals(""))
{

}

http://stackoverflow.com/questions/2601978/how-to-check-if-my-string-is-equal-to-null — Yaneeve, Mar 31 '11 at 12:28
insignificant but, string.length() == 0 is probably better than say equals to "" — MeBigFatGuy, Mar 31 '11 at 13:03

score 42 · Accepted Answer · answered Mar 31 '11 at 12:26

42

Checking for null is done via if (string != null)

If you want to check if its null or empty - you'd need if (string != null && !string.isEmpty())

I prefer to use commons-lang StringUtils.isNotEmpty(..)

answered Mar 31 '11 at 12:26

Bozho

588,226
146
1,060
1,140

2

+1 for StringUtils, again. Everyone of us should spend a couple of minutes a day reading what apache commons can do for us! – Pablo Grisafi Mar 31 '11 at 15:40

score 5 · Answer 2 · answered Mar 31 '11 at 12:26

5

You can do it with the following code:

 if (string != null) {

 }

answered Mar 31 '11 at 12:26

RoflcoptrException

51,941
35
152
200

score 2 · Answer 3 · edited Apr 10 '18 at 00:11

Nothing really new to add to the answers above, just wrapping it into a simple class. Commons-lang is quite all right but if all you need are these or maybe a few more helper functions, rolling your own simple class is the easiest approach, also keeping executable size down.

public class StringUtils {

  public static boolean isEmpty(String s) {
    return (s == null || s.isEmpty());
  }

  public static boolean isNotEmpty(String s) {
    return !isEmpty(s);
  }
}

score 2 · Answer 4 · answered Mar 31 '11 at 12:31

2

Checking for null is done by:

string != null

Your example is actually checking for the empty string

You can combine the two like this:

if (string != null && !string.equals("")) { ...

But null and empty are two different things

answered Mar 31 '11 at 12:31

brain

5,496
1
26
29

score 1 · Answer 5 · edited Jun 28 '17 at 06:02

1

if(str != null && !str.isEmpty())

Be sure to use the parts of && in this order, because java will not proceed to evaluating the the second if the first part of && fails, thus ensuring you will not get a null pointer exception from str.isEmpty() if str is null.

Beware, it's only available since Java SE 1.6.

You have to check str.length() == 0 or str.equals("") on previous versions.

edited Jun 28 '17 at 06:02

Jarvis

8,494
3
27
58

answered Oct 14 '13 at 13:08

Kalpana

491
1
7
21

Kishan Vaghela · Answer 6 · 2015-09-06T13:10:04.860

1

Use TextUtils Method.

TextUtils.isEmpty(str) : Returns true if the string is null or 0-length. Parameters: str the string to be examined Returns: true if str is null or zero length

if(TextUtils.isEmpty(str)){
    // str is null or lenght is 0
}

Source of TextUtils class

isEmpty Method :

 public static boolean isEmpty(CharSequence str) {
        if (str == null || str.length() == 0)
            return true;
        else
            return false;
    }

edited Sep 06 '15 at 13:10

answered Mar 09 '15 at 06:02

Kishan Vaghela

7,678
5
42
67

U can found here : http://developer.android.com/reference/android/text/TextUtils.html – Kishan Vaghela Sep 06 '15 at 13:05

score 0 · Answer 7 · edited Jun 20 '20 at 09:12

0

The best way to check a String is :

import org.apache.commons.lang3.StringUtils;

if(StringUtils.isNotBlank(string)){
....
}

From the doc :

isBlank(CharSequence cs) :

Checks if a CharSequence is empty (""), null or whitespace only.

edited Jun 20 '20 at 09:12

Community

1
1

answered May 26 '18 at 07:52

aayoustic

99
9

You should specify its library full name, Commons, and be more specific on the method behaviour. Imho, you should improve the answer a bit. Regards – Fabiano Tarlao May 26 '18 at 08:17
1

@FabianoTarlao Sure buddy, have updated the answer ! – aayoustic May 28 '18 at 05:27

score 0 · Answer 8 · answered Mar 31 '11 at 14:54

As everyone is saying, you'd have to check (string!=null), in objects you're testing the memory pointer.

because every object is identified by a memory pointer, you have to check your object for a null pointer before testing anything else, so:

(string!=null && !string.equals("")) is good

(!string.equals("") && string !=null) can give you a nullpointerexception.

if you don't care for trailing spaces you can always use trim() before equals() so " " and "" gives you the same result

score 0 · Answer 9 · answered Sep 09 '19 at 06:47

You can use Predicate and its new method (since java 11) Predicate::not

You can write code to check if string is not null and not empty:

Predicate<String> notNull = Predicate.not(Objects::isNull);
Predicate<String> notEmptyString = Predicate.not(String::isEmpty);
Predicate<String> isNotEmpty = notNull.and(notEmptyString);

Then you can test it:

System.out.println(isNotEmpty.test(""));      // false
System.out.println(isNotEmpty.test(null));    // false
System.out.println(isNotEmpty.test("null"));  // true

score 0 · Answer 10 · answered Oct 04 '20 at 18:05

A common way for testing null string in Java is with Optionals:

Optional.ofNullable(myString).orElse("value was null")

Optional.ofNullable(myString).ifPresent(s -> System.out.println(s));

Optional.ofNullable(myString).orElseThrow(() -> new RuntimeException("value was null"));

And to test if it is null or empty you can use Apache org.apache.commons.lang3 library that gives you the following methods:

StringUtils.isEmpty(String) / StringUtils.isNotEmpty(String): It tests if the String is null or empty (" " is not empty)
StringUtils.isBlank(String) / StringUtils.isNotBlank(String): Same as isEmpty bt if the String is only whitespace it is considered blank

And applied to Optional you get:

Optional.ofNullable(myString).filter(StringUtils::isNotEmpty).orElse("value was null or empty");

Do not do this. It is only complicated without any benefit over the accepted answer. — Donat, Oct 04 '20 at 20:32
It's a one-liner that does the same as ```java if(myString != null){ ... } ``` That you find it complicated it's a thing but I assume you find Java lambda complicated to read too ? — m4nu56, Oct 05 '20 at 20:30

score 0 · Answer 11 · edited Aug 01 '22 at 18:03

0

Try using Strings.isNullOrEmpty("") from com.google.common.base.Strings this method returns boolean value and checks for both null and empty string.

edited Aug 01 '22 at 18:03

Ashok kumar Ganesan

1,098
5
20
48

answered Jul 29 '22 at 15:52

Sanjay Rao

9
4

score -2 · Answer 12 · answered Mar 31 '11 at 12:28

-2

if(string != null)

or

if(string.length() == 0)

or

if(("").equals(string))

answered Mar 31 '11 at 12:28

David Machel

286
2
12

2

Not really. Only the first is really true. – RoflcoptrException Mar 31 '11 at 12:30

Akshatha · Answer 13 · 2013-03-23T07:56:49.480

-4

u can try this

if(string != null)

edited Mar 23 '13 at 07:56

answered Mar 31 '11 at 12:29

Akshatha

599
2
10
26

what about multiple spaces – Nayn Mar 21 '13 at 12:19

How to check a string is not null?

13 Answers13

Linked