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Check whether a string is not null and not empty


Question

How can I check whether a string is not null and not empty?

public void doStuff(String str)
{
    if (str != null && str != "**here I want to check the 'str' is empty or not**")
    {
        /* handle empty string */
    }
    /* ... */
}
2017/09/12
1
495
9/12/2017 6:26:53 PM

Accepted Answer

What about isEmpty() ?

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

Be sure to use the parts of && in this order, because java will not proceed to evaluate the second part 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 on previous versions.


To ignore whitespace as well:

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

(since Java 11 str.trim().isEmpty() can be reduced to str.isBlank() which will also test for other Unicode white spaces)

Wrapped in a handy function:

public static boolean empty( final String s ) {
  // Null-safe, short-circuit evaluation.
  return s == null || s.trim().isEmpty();
}

Becomes:

if( !empty( str ) )
2018/10/06
900
10/6/2018 8:16:20 PM

Use org.apache.commons.lang.StringUtils

I like to use Apache commons-lang for these kinds of things, and especially the StringUtils utility class:

import org.apache.commons.lang.StringUtils;

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

if (StringUtils.isBlank(str)) {
    ...
} 
2020/06/20

Just adding Android in here:

import android.text.TextUtils;

if (!TextUtils.isEmpty(str)) {
...
}
2013/01/24

To add to @BJorn and @SeanPatrickFloyd The Guava way to do this is:

Strings.nullToEmpty(str).isEmpty(); 
// or
Strings.isNullOrEmpty(str);

Commons Lang is more readable at times but I have been slowly relying more on Guava plus sometimes Commons Lang is confusing when it comes to isBlank() (as in what is whitespace or not).

Guava's version of Commons Lang isBlank would be:

Strings.nullToEmpty(str).trim().isEmpty()

I will say code that doesn't allow "" (empty) AND null is suspicious and potentially buggy in that it probably doesn't handle all cases where is not allowing null makes sense (although for SQL I can understand as SQL/HQL is weird about '').

2012/10/30

str != null && str.length() != 0

alternatively

str != null && !str.equals("")

or

str != null && !"".equals(str)

Note: The second check (first and second alternatives) assumes str is not null. It's ok only because the first check is doing that (and Java doesn't does the second check if the first is false)!

IMPORTANT: DON'T use == for string equality. == checks the pointer is equal, not the value. Two strings can be in different memory addresses (two instances) but have the same value!

2010/08/30

Almost every library I know defines a utility class called StringUtils, StringUtil or StringHelper, and they usually include the method you are looking for.

My personal favorite is Apache Commons / Lang, where in the StringUtils class, you get both the

  1. StringUtils.isEmpty(String) and the
  2. StringUtils.isBlank(String) method

(The first checks whether a string is null or empty, the second checks whether it is null, empty or whitespace only)

There are similar utility classes in Spring, Wicket and lots of other libs. If you don't use external libraries, you might want to introduce a StringUtils class in your own project.


Update: many years have passed, and these days I'd recommend using Guava's Strings.isNullOrEmpty(string) method.

2017/06/01

Source: https://stackoverflow.com/questions/3598770
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