Can we rely on String.isEmpty for checking null condition on a String in Java?

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?

Solution 1:

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))

Solution 2:

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.

Solution 3:

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()));
}

Solution 4:

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.

Solution 5:

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