73

I am passing an accountid as input from an XML file as shown, which will be parsed later and will be used in our code:

<accountid>123456</accountid>
<user>pavan</user>

The issue is that if nothing is passed (null value in accoutnid) is passed as accountid, I could not able to handle that situation in Java code. I tried this but I was not successful:

if (acct != null||acct==""||acct.equals("")) 
{
    // the above is not working 
}

I was able to handle this successfully using the following approach:

if(!acct.isEmpty())
{
   // thisis working 
}

Can we rely on the String.isEmpty() method for checking the null condition of a String? Is this valid?

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7 Answers 7

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172

No, absolutely not - because if acct is null, it won't even get to isEmpty... it will immediately throw a NullPointerException.

Your test should be:

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

Note the use of && here, rather than your || in the previous code; also note how in your previous code, your conditions were wrong anyway - even with && you would only have entered the if body if acct was an empty string.

Alternatively, using Guava:

if (!Strings.isNullOrEmpty(acct))
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7 Comments

Some also like this version of the same check: "".equals(acct)
Hi Jon , I tried with a sample Program , String str = ""; System.out.println(str.isEmpty()); , here it returned true , it didn't throw NullPointerException . so why cant we use isEmpty for Checking Null values ?? Could you please clarify this ??
@Kiran: Because "" isn't the same as a null reference. Try it with String str = null; and then you'll get a NullPointerException. It's very important to understand the difference between a string reference which is null and a string reference which refers to an empty string.
@AlexZam: You'd still want to also check whether it's null. The point is to check whether the string has any content.
Thank you Jon , i tried with this code you told , if (acct != null && !acct.isEmpty()) , but still it is not able to handle when no accountid is passed .
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37

Use StringUtils.isEmpty instead, it will also check for null.

Examples are:

 StringUtils.isEmpty(null)      = true
 StringUtils.isEmpty("")        = true
 StringUtils.isEmpty(" ")       = false
 StringUtils.isEmpty("bob")     = false
 StringUtils.isEmpty("  bob  ") = false

See more on official Documentation on String Utils.

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3 Comments

Link only answers should be posted as comments instead
but therefore i need more reputation
StringUtils.isEmpty() is deprecated now!!! ;(
9

You can't use String.isEmpty() if it is null. Best is to have your own method to check null or empty. 

public static boolean isBlankOrNull(String str) {
    return (str == null || "".equals(str.trim()));
}
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4 Comments

I would recommend using StringUtils from commons-lang instead of writing your own.
+1 I would not recommend adding commons-lang to your project (unless you are already including it) only for such a simple method.
Reading the above answers, how about str == null || str.trim().isEmpty()?
@ardila which is exactly what this answer is checking
3

No, the String.isEmpty() method looks as following:

public boolean isEmpty() {
    return this.value.length == 0;
}

as you can see it checks the length of the string so you definitely have to check if the string is null before.

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2

I think the even shorter answer that you'll like is: StringUtils.isBlank(acct);

From the documentation: http://commons.apache.org/proper/commons-lang/javadocs/api-2.6/org/apache/commons/lang/StringUtils.html#isBlank%28java.lang.String%29

isBlank
public static boolean isBlank(String str)
Checks if a String is whitespace, empty ("") or null.

 StringUtils.isBlank(null)      = true
 StringUtils.isBlank("")        = true
 StringUtils.isBlank(" ")       = true
 StringUtils.isBlank("bob")     = false
 StringUtils.isBlank("  bob  ") = false
 
Parameters:
str - the String to check, may be null
Returns:
true if the String is null, empty or whitespace
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1 
String s1=""; // empty string assigned to s1 , s1 has length 0, it holds a value of no length string

String s2=null; // absolutely nothing, it holds no value, you are not assigning any value to s2

so null is not the same as empty.

hope that helps!!!

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1 Comment

The Question is not about whether Null and empty are same. The OP is instead asking if he can rely on String isEmpty method to check for null.
0

You could use TextUtils.isEmpty to check both nullable and empty string.

TextUtils.isEmpty(acct)

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