String null check

Question

I have tried this for 2 hours , but I've given up. I am checking the value of a String this way:

if(value.equals("")||value.length()<0||value==null)
{
    value = "Anynomous"
}

But still the string is printing the value null.

Please see this program code here

<HTML>
<BODY>

<%!
String value ;
%>

<%

value = (String)request.getAttribute("retunval");
System.out.println("Inside New fgdf JSP");
if(value.equals("")||value.length()<0||value==null)
value = "Anonymuos";


%>
Hello <%=value%>

<BR>
</BR>

<BR>
</BR>

<a href="Test.jsp">Try Again</a>
</BODY>
</HTML>

Try this: if (value==null || value.trim().length()==0 || value.equalsIgnoreCase("null")) {value = "Anonymuos";} — Alex K
– Alex K, Commented Sep 23, 2011 at 12:00
Your order of conditions is wrong, First check ==null. In this case if value == null you gets NullPointerException because of value.equals("") is executed first. if (value == null || value.length() == 0) value = "Anonymous"; should be OK. Likely you set value by string "null" somewhere somehow. For example value = String.format("%s", somethingThatIsNull) will result in value == "null". — Salw
– Salw, Commented Sep 23, 2011 at 12:00
possible duplicate of One step check for null value & emptiness of a string — Alex K.
– Alex K., Commented Sep 23, 2011 at 12:03

ig0774 · Accepted Answer · 2011-09-23 11:58:55Z

5

Check whether value is null first. Otherwise value.equals() will throw a NullPointerException.

 if (value == null || value.equals("")) {
     value = "Anonymous";
 }

answered Sep 23, 2011 at 11:58

ig0774

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1 Comment

ig0774 Over a year ago

@ante.sabo: True, but it's probably actually better to use something like Apache Commons StringUtils#isBlank() to cover that, as others suggested...

Thomas · Accepted Answer · 2011-09-23 11:58:53Z

3

First you need to reorder your if condition, otherwise you could run into NPEs. Additionally, the string length can never be lower than 0, so that check is not needed:

value==null||value.equals("")

Alternatively, if you can use Apache Commons Lang you could use StringUtils.isEmpty(value) which handles all the relevant cases for you.

answered Sep 23, 2011 at 11:58

Thomas

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Comments

Ed Staub · Accepted Answer · 2011-09-23 12:24:53Z

3

You need to add

||value.equals("null")

Somewhere something already did a toString() on the null value. Note the other answers as well - but this is the cause of the specific problem you're reporting.

So you'd end up with, as one option:

if ( value==null || value.isEmpty() || "null".equals(value) )

Because of the null-check, inverting the .equals() isn't necessary in this case - but it's a good habit to get into.

edited Sep 23, 2011 at 12:24

answered Sep 23, 2011 at 12:00

Ed Staub

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1 Comment

Ash Over a year ago

its still a good practice to always use a literal as the first operand in equals comparison

Ankit Bansal · Accepted Answer · 2014-05-23 04:30:18Z

2

i think

value = (String)request.getAttribute("retunval");

is returning you a "null" string. When you try to do if tests that you have mentioned, it will return false because you are not checking

value.equals("null")

so that's why you get output as null.

edited May 23, 2014 at 4:30

answered Sep 23, 2011 at 12:00

Ankit Bansal

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3 Comments

Ed Staub Over a year ago

While the fix is correct, the diagnosis is not. "null" is not a null string. It's not returning a null string - it's returning the 4-character string "null".

Ash Over a year ago

all is well in this world and this is the accepted answer but i would just like to add here that while string checks its should always be "null".equals(value). i.e. the literal should always be the first operand.. that way you avoid NullPointerException

Ankit Bansal Over a year ago

by null string, i also meant "null" string only and I think that is too obvious based on the check value.equals("null") I have talked about.

Sean Patrick Floyd · Accepted Answer · 2011-09-23 11:59:24Z

1

if(value.equals("")||value.length()<0||value==null)
  value = "Anynomous"

The second and third condition can never evaluate to true! (A String's length can never be less than zero, and if value was null, value.equals("") would have caused a NullPointerException)

try this instead:

if(value==null||"".equals(value))

answered Sep 23, 2011 at 11:59

Sean Patrick Floyd

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Comments

Péter Török · Accepted Answer · 2011-09-23 11:59:45Z

1

value.length()<0 will never be true - use value.length()==0 instead. However, in this case, the previous check (value.equals("")) is equivalent to this one, so you can omit it. Apart from this, the condition should detect empty/null strings (except that the null check should be first, to avoid dereferencing a null pointer).

Is it possible that value contains the text "null"?

answered Sep 23, 2011 at 11:59

Péter Török

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Comments

Mike C · Accepted Answer · 2011-09-23 12:00:35Z

0

Is it possible that the value of the string is 'null'? (That is, not null, but a string which reads 'null')

answered Sep 23, 2011 at 12:00

Mike C

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Sean Patrick Floyd · Accepted Answer · 2011-09-23 12:03:33Z

0

Reorder as Thomas and ig0774 suggested or use the StringUtils.isEmpty() method of Apache Commons Lang.

edited Sep 23, 2011 at 12:03

Sean Patrick Floyd

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answered Sep 23, 2011 at 12:02

palacsint

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2 Comments

mrkhrts Over a year ago

Using a third-party library for something as simple as checking for null seems a little superfluous to me.

palacsint Over a year ago

Checking for null and empty string. I think the code is more readable with StringUtils and there are other useful method in this lib. With maven just a few clicks to import a dependency, it's a not a big deal.

Satya · Accepted Answer · 2011-09-23 12:22:28Z

0

Use this :

   if(value == null || value.trim().length() <=0 || value.trim().equals("null")){
     value ="Ananymous";
   }

edited Sep 23, 2011 at 12:22

answered Sep 23, 2011 at 12:08

Satya

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Comments

Ganesh Varahade · Accepted Answer · 2011-09-23 12:34:35Z

0

I think this would be the best condition to check for it

if(value==null || value.trim().length()==0 || value.equals("null"))

it also eliminate fact if value=" " contains spaces.

answered Sep 23, 2011 at 12:34

Ganesh Varahade

1

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