Android Java exception even after string null or empty check

Question

I really don't understand why java.lang.NumberFormatException: Invalid long: "null" happens here.

The problem snippet is like followings.

try {
        userid = ((JSONObject) msg.obj).getString("userid");
        if (userid.equals("") || userid.isEmpty() || null==userid) {
                onClickLogout();
                return;
        } else {
            client.setUserid(Long.parseLong(userid));
       }
    } catch (JSONException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
            onClickLogout();
            return;
    }

the line client.setUserid(Long.parseLong(userid)); gets following exception

java.lang.NumberFormatException: Invalid long: "null"
at java.lang.Long.invalidLong(Long.java:125)
at java.lang.Long.parse(Long.java:362)
at java.lang.Long.parseLong(Long.java:353)
at java.lang.Long.parseLong(Long.java:319)
at client.setUserid(Long.parseLong(userid));

The point is that the null exception occurs even after null and empty check of the userid in the code. What's wrong with me here? please check it out experts!

Check first if the userid is null instead of calling equals otherwise you may run into a NPE — Pedro Oliveira
– Pedro Oliveira, Commented Oct 10, 2014 at 14:43
I've edited your question, please check. This could avoid a possible NullPointerException. In addition, you should add @laalto 'sanswer. — Juan Aguilar Guisado
– Juan Aguilar Guisado, Commented Oct 10, 2014 at 14:49
Oops, thank you. It was my first edit. I didn't know this. Sorry — Juan Aguilar Guisado
– Juan Aguilar Guisado, Commented Oct 10, 2014 at 15:05
Thanks guys! The strange thing here is that userid = ((JSONObject) msg.obj).getString("userid"); gets only "" or some numbers. "" case covers that there is no related userid number. the null case is sort of impossible case here actually. and this case happens in rare. I've seen this case just through google report. I'll try @laalto 's solution this time. Thanks! — Marcel Kim
– Marcel Kim, Commented Oct 10, 2014 at 15:39

laalto · Accepted Answer · 2014-10-10 14:43:59Z

2

The string value and not reference is null.

You can add "null".equals(userid) to test for the literal null value in the if where you check for various forms of "no value".

answered Oct 10, 2014 at 14:43

laalto

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1 Comment

Marcel Kim Over a year ago

Thanks guys! The strange thing here is that userid = ((JSONObject) msg.obj).getString("userid"); gets only "" or some numbers. "" case covers that there is no related userid number. the null case is sort of impossible case here actually. and this case happens in rare. I've seen this case just through google report. I'll try your solution this time. Thanks!

ToYonos · Accepted Answer · 2014-10-10 14:47:42Z

2

Always check first for null value in your condition

if (null==userid || userid.isEmpty() || userid.equals("null") {

Then, in the next element of your condition, you are sure that userid is not null and no NullPointerException will be thrown

Also, in your case, check that userid does not contain the "null" String

Moreover userid.equals("") and userid.isEmpty() are the same thing.

answered Oct 10, 2014 at 14:47

ToYonos

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1 Comment

Marcel Kim Over a year ago

Thanks for your comment! laalto stole your thunder!

Dovydas Šopa · Accepted Answer · 2016-05-25 07:05:13Z

0

You can check null with utility method isEmpty from TextUtils,

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

isEmpty(CharSequence str) method check both condition, for null and length.

edited May 25, 2016 at 7:05

Dovydas Šopa

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answered May 25, 2016 at 6:19

NSK

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