null value in if condition and null pointer exception java

Question

I want to do something like below in java.

String subject=null,receiver=null,subject_db=null,receiver_db=null,cc=null,cc_db=null;
suject=msg.getSubject();
sub_db=rs.getString("subject");
receiver=msg.getreceiver();
receiver_db=rs.getString("receiver");
cc=msg.getcc();
cc_db=rs.getString("cc"); String foldername;

if((subject.equals(sub_db)) && (receiver.equals(receiver_db)) && (cc.equals(cc_db)))
  foldername="spam";
else
  foldername="Inbox";

As you can see here, any of the variables can be null. If this happens then it throws me NullPointerException. Is there any way I can do like, String s1=null and String s2=null and if I compare if(s1.equals(s2)) then it returns me true... I know above code is not gonna work to achieve this. But how do I do that in some other way ?

I am really sorry if I have failed to explain my problem properly...

I would appreciate any help..

Thank you..

nybbler · Accepted Answer · 2012-02-16 16:06:34Z

4

How about something like…

private boolean nullsOrEquals(string s1, string s2)
{
  if (s1 == null)
    return (s2 == null);

  return s1.equals(s2);
}

if (nullsOrEquals(subject, sub_db) && [etc])
  foldername="spam";
else
  foldername="Inbox";

edited Feb 16, 2012 at 16:06

nybbler

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answered Feb 16, 2012 at 16:00

raveturned

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Comments

ggrigery · Accepted Answer · 2012-02-16 16:27:31Z

3

if((s1 == null && s2 == null) || s1.equals(s2))

edited Feb 16, 2012 at 16:27

answered Feb 16, 2012 at 15:54

ggrigery

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4 Comments

Buhake Sindi Over a year ago

This should be a comment. No? :p

ggrigery Over a year ago

Or more precisely, to cover your example and avoid the NPE... if((s1 == null & s2 == null) || s1.equals(s2))

ggrigery Over a year ago

@Elite, Sorry, just joined and can't comment until I get some rep :( Try to help when I can but I'm only able to post answers at the moment.

Mooing Duck Over a year ago

Edit the full expression into the answer please

STM · Accepted Answer · 2012-02-16 15:57:10Z

1

If I understand you want to compare Strings even if they are null.

For that just add a condition in the if statement like:

if((string1 == null && string2==null) || string1.equals(s2))
{
//Your code
}

answered Feb 16, 2012 at 15:57

STM

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1 Comment

Ragini Over a year ago

Thanks all for your response..Finally I ddid it like. private static boolean nullsOrEquals(String s1, String s2) { if(s1 == null) { if(s2 == null) { return true; } return false; } if(s2 == null) { return false; } return s1.equals(s2); }

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