Null String and Empty String problem

Hello everyone,
since i am totally new in JSP, i am getting problem in handling strings.
Suppose i have a variable users = ""; then
I want to ask when to use:
if (users.equals(""))
and
if(users == "")
in my code, variable users has value "regional" for regional users.
and i am checking this code as:
if (users.equals{"regional")) {
out.print ("I am inside code");
at that time, the code is throwing error (run time error)
and when i changed the code as:
if (users == "regional") {
out.print ("I am inside code");
this time, the code is not generating error but the part message "I am inside code " is not displaying. The code do not inserts inside the if condition
I hope u understand my problem. Can anybody help me out with this.

This has basically nothing to do with JSP, but with basic Java knowledge.
When using the '==' operator to compare Objects (yes, String is actually a subclass of Object), then it will look if they are of the same reference. Using the '==' operator to compare primitive datatypes (int, boolean, char, etc) will look if they have the same value.
That is why the Object class has the equals() method to give the ability compare with another objects. And you can only invoke it when the Object is actually instantiated. So if it is not null.
if (string != null && string.equals("somevalue")) {
// or
if ("somevalue".equals(string)) {
}should work.
Edit rym82: this will not throw a NPE, but an ordinary compilation error ;)
Message was edited by:
BalusC

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Find out varchar2 string NULL columns and Empty columns

Hi dev's ,
my requiremnt is to find out the string columns Names of whose storing NULL values and EMPTY strings. for that i had written below code. it's getting some error.
SET ECHO OFF;
SET FEEDBACK OFF;
SET SERVEROUTPUT ON;
SET VERIFY OFF;
SET PAGES 0;
SET HEAD OFF;
spool D:\stringnull.csv
DECLARE
v_tab_indent NUMBER(5);
v_col_indent NUMBER(5);
v_val1       VARCHAR2(20);
v_val2       VARCHAR2(20);
v_query1     VARCHAR(500);
v_query2     VARCHAR(500);
BEGIN
--DBMS_OUTPUT.ENABLE(100000);
SELECT MAX(LENGTH(table_name))+1,MAX(LENGTH(column_name))    +1
INTO v_tab_indent,v_col_indent
FROM user_tab_columns
WHERE data_type='VARCHAR2';
FOR i IN
(SELECT table_name,
    column_name
FROM user_tab_columns
WHERE data_type IN ('NVARCHAR2', 'CHAR', 'NCHAR', 'VARCHAR2')
ORDER BY table_name,
    column_name
LOOP
    v_query1:='SELECT NVL('||i.column_name||',0) AS VAL
              FROM '||i.table_name||' where '||i.column_name||' IS NULL';
    v_query2:='SELECT '||i.column_name||' AS VAL
              FROM '||i.table_name||' where '||i.column_name||'=''''';
    --dbms_output.put_line(v_query1);
   -- dbms_output.put_line(v_query2);
    EXECUTE immediate v_query1 INTO v_val1;
    EXECUTE immediate v_query2 INTO v_val2;
    dbms_output.put_line (rpad(i.table_name,v_tab_indent,' ')||','||rpad(i.column_name,v_col_indent,' ')||' ,'||v_val1||','||v_val2);
END LOOP;
END;
Spool OFF
Set echo on
Set feedback onERROR:
Error report:
ORA-01403: no data found
ORA-06512: at line 31
01403. 00000 - "no data found"
*Cause:
*Action:
set feedback onpls help me on this issue..
Thanks,

Example:
SQL> DECLARE
2    v_val       VARCHAR2(20);
3    v_query1     VARCHAR(32767);
4 BEGIN
5   FOR i IN (SELECT table_name, column_name FROM user_tab_columns
6             WHERE data_type IN ('NVARCHAR2', 'CHAR', 'NCHAR', 'VARCHAR2')
7             ORDER BY table_name, column_name
8            )
9   LOOP
10     v_query1 := 'SELECT count(*) FROM '||i.table_name||' where '||i.column_name||' IS NULL';
11     EXECUTE immediate v_query1 INTO v_val;
12     dbms_output.put_line(rpad(i.table_name,30,' ')||' : '||rpad(i.column_name,30,' ')||' : '||v_val);
13   END LOOP;
14 END;
15 /
CHILD_TAB                      : DESCRIPTION                    : 0
DEPT                           : DNAME                          : 0
DEPT                           : LOC                            : 0
EMP                            : ENAME                          : 0
EMP                            : JOB                            : 0
MYEMP_OLD                      : ENAME                          : 0
MYEMP_OLD                      : JOB                            : 0
MYNULLS                        : ENAME                          : 0
MYNULLS                        : JOB                            : 4
PARENT_TAB                     : DESCRIPTION                    : 0
T                              : CHAR_VALUE                     : 0
TABLE1                         : COL1_DESC                      : 0
PL/SQL procedure successfully completed.

Difference between null vector and empty Vector

What is the diffrence between null vector and empty vector.

null vector means the JVM doesn't allocate memory.It doesn't exist
in memory. NO instance!
empty vector means the JVM allocated memory.It exists in memory.
it's a instance than is accessabel.But only have on elements.
GL&HF.

Oracle, Null and empty Strings

Currently I'm facing problems with a class, which contains a String, which
is set to "" (empty String).
When the class is persistent, oracle writes null to the table column
(which seems to be common oracle behaviour) and when retrieving the class,
the field is set to null as well, giving me a lot of null-pointer
exceptions.
Anyway ... I can cope with that (just a lot of extra work)
far worse is the problem, wenn searching objects, that have this field set
to "" oder null.
Oracle can't find the records because JDO creates Querys "where
string=null" or "where string=''" , where oracle expects "where string is
null" to find the records.
Is there a workaround or solution ?

Yeah, that would work as well, thx, but since I have to cope with
null-Strings now everywhere in my program, it doesn't hurt just to forbid
empty strings on the program side.
In future times I'll test on Oracle first, then porting to DB/2 - this way
I suppose work is far less to garant compability.
Nevertheless ... having to set the bankcode into quotes is a kodo bug in
my opinion.
Kodo knows the type of classfields (in this case string) and shouldn't
send the parameter as a BigDecimal to the database.
Given that, and having only bankcodes of null (only neccesary when using
Oracle), the method would look like:
public Collection getAccounts (String bankCode)
throws Exception
return getAccounts (Account.class, "bankcode=="+bankcode);
which is how a transparent persistent layer, um, should be , um , I mean
... just transparent ;-D
Marc Prud'hommeaux wrote:
Stefan-
Couldn't you just do something like:
public Collection getAccounts (String bankCode)
throws Exception
String filter;
if (bankCode == null || bankCode.length () == 0)
filter = "(bankCode == null || bankCode == "")";
else
filter = "bankCode == "" + bankCode + """;
return getAccounts (Account.class, filter);
If I understand the problem correctly, this should work for all the
databases.
In article <[email protected]>, Stefan wrote:
What operations are you performing to cause this SQL to be issued? You
say you are having trouble removing objects, but this is clearly not a
DELETE statement. Is this the SQL that is issued when looking up
objects by identity?I'm not removing objects, I was removing just quotes from parameters ;-)
A string column... is it also represented as a string field in your class?Yeah ... just to give you an impression of the code:
First we have a class, representing a bank account:
public class Account {
private AccountMgr myAccountMgr;
private String bankCode;
private String id;
Note, that in nearly all cases bankCode will be a number or null.
I have a second class "AccountMgr", which does all of the persistant stuff
(seaching, making persistent etc.)
This class has two methods, one versatile (protected) to retrieve accounts
by a given filterString and one who just returns accounts by bankCode,
building the expected filterstring. Here is my current working version:
public class AccountMgr {
public Collection getAccounts(String bankCode) throws Exception {
if (bankCode!=null) {
if (bankCode.equals("")) {
throw new Exception("check code, bankCode='' not allowed to get
same behavior from DB2 and Oracle");
// if set, quote the bankCode
bankCode="""+bankCode+""";
return getAccounts(Account.class,"bankCode=="+bankCode);
protected Collection getAccounts(Class accountClass, String filterAdd)
throws Exception {
PersistenceManager pm = MyHelper.getPersistenceManager();
String filter="";
if (filterAdd!=null && !filterAdd.trim().equals("")) {
filter+=filterAdd + " && ";
filter += "myAccountMgr==_accMgr";
Query query = pm.newQuery(accountClass, filter);
query.declareParameters("AccountMgr _accMgr");
return (Collection) query.execute(this);
As you can see, in the first method I have to set the bankCode into
quotes, when it's not null.
This is because otherwise a filter like "bankCode=1234" will be translated
in a way, where 1234 is send as a BigDecimal to the database:
[...] executing statement <4239745>: (SELECT [...] FROM JDO_ACCOUNT t0
WHERE t0.BANKCODE = ? : [reused=1;params={(BigDecimal) 1234}]
Marc Prud'hommeaux [email protected]
SolarMetric Inc. http://www.solarmetric.com

How to distinguish NULL and Empty Strings

Hi,
Just to set the context right; I'm an experienced C programmer trying labview for the first time. As such I ran in to a problem being that Labview has no concept of NULL-pointers and more specifically appears to have no concept of the difference between a NULL-string and an empty-string
I'm trying to make a structure (bundle) of strings (in it's most basic form key-value pairs) which i'd like to (for instance) URI encode in order to send it to a web server. For those who are not familiar with URI encoding; there is a distinguished difference between setting a key to an empty string and setting a key with no value. In C I would use a pointer to an empty string vs a NULL string pointer to symbolize this.
In essence I need an elegant way to distinguish between a defined but empty string and an undefined string (hmmm this is actually describing the same problem but now in terms of perl).
Anybody have any pointers (pun not intended) for me ?

This is a bit depending on the interface you have with your encoder. The whole issue is that LV has no pointers at all (and you will like it, as you will never have any Null-Pointer exeptions and the like).
Assuming that you use a dll (so the Call Library node).
Use CString as input -> NULL-Terminated String.
Use I32 as input and pass 0 -> NULL string.
Felix
www.aescusoft.de
My latest community nugget on producer/consumer design
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NULL and Empty String

Hi There,
As far as I know, Null is not the same as an empty string; however, when I try this out, I get some unexpected results (well, at least unexpected for my liking):
SQL> CREATE TABLE TS (MID NUMBER,
2 MDESC VARCHAR2(20) DEFAULT '' NOT NULL);
Table created.
SQL> INSERT INTO TS VALUES(1,'');
INSERT INTO TS VALUES(1,'')
ERROR at line 1:
ORA-01400: cannot insert NULL into ("TT"."TS"."MDESC")So, according to the above scenario, I can't insert an empty string!! However, an empty string is a valid string that doesn't have tuples/data!!
How come Oracle translates the null string '' as NULL?
Thanks

William Robertson wrote:
There is a special case to do with CHAR values, whereby '' counts as a string and so gets blank-padded, whereas NULL does not.Are you referring to:
SQL> DECLARE
2      flag CHAR(2);
3      PROCEDURE check_null (p_flag IN CHAR)
4      IS
5      BEGIN
6        IF p_flag = ' '
7        THEN
8          dbms_output.put_line ('flag is equal to '' ''');
9        ELSIF p_flag IS NULL
10        THEN
11          dbms_output.put_line ('flag is null');
12        ELSE
13          dbms_output.put_line ('other');
14        END IF;
15      END;
16    BEGIN
17      flag := '';
18      check_null (flag);
19      flag := NULL;
20      check_null (flag);
21    end;
22 /
flag is equal to ' '
flag is null
PL/SQL procedure successfully completed.
SQL> alter session set events '10932 trace name context forever, level 16384';
Session altered.
SQL> DECLARE
2      flag CHAR(2);
3      PROCEDURE check_null (p_flag IN CHAR)
4      IS
5      BEGIN
6        IF p_flag = ' '
7        THEN
8          dbms_output.put_line ('flag is equal to '' ''');
9        ELSIF p_flag IS NULL
10        THEN
11          dbms_output.put_line ('flag is null');
12        ELSE
13          dbms_output.put_line ('other');
14        END IF;
15      END;
16    BEGIN
17      flag := '';
18      check_null (flag);
19      flag := NULL;
20      check_null (flag);
21    end;
22 /
flag is null
flag is null
PL/SQL procedure successfully completed.
SQL> SY.
P.S. Don't ask me why normal (or at least consistent) behavior is not the default.

Null and empty string not being the same in object?

Hello,
I know that null and empty string are interpreted the same in oracle.
However I discovered the strange behaviour concerning user defined objects:
create or replace
TYPE object AS OBJECT (
value VARCHAR2(2000)
declare
xml xmltype;
obj object;
begin
obj := object('abcd');
xml := xmltype(obj);
dbms_output.put_line(xml.getStringVal());
obj.value := '';
xml := xmltype(obj);
dbms_output.put_line(xml.getStringVal());
obj.value := null;
xml := xmltype(obj);
dbms_output.put_line(xml.getStringVal());
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When creating xml from object, all not-null fields are transformed into xml tag.
I supposed that obj.value being either '' or null will lead to the same result.
However this is output from Oracle 9i:
<OBJECT_ID><VALUE>abcd</VALUE></OBJECT_ID>
<OBJECT_ID><VALUE></VALUE></OBJECT_ID>
<OBJECT_ID/>
Oracle 10g behaves as expected:
<OBJECT><VALUE>abcd</VALUE></OBJECT>
<OBJECT/>
<OBJECT/>
However Oracle 9i behaviour leads me to the conclusion that oracle
must somehow distinguish between empty string and null in user defined objects...
Can someone clarify this behaviour?
Thus is it possible to test if object's field is empty or null?

However Oracle 9i behaviour leads me to the conclusion that oracle
must somehow distinguish between empty string and null in user defined objects...
Can someone clarify this behaviour?
Thus is it possible to test if object's field is empty or null?A lot of "fixes" were done, relating to XML in 10g and the XML functionality of 9i was known to be buggy.
I think you can safely assume that null and empty strings are treated the same by Oracle regardless. If you're using anything less than 10g, it's not supported any more anyway, so upgrade. Don't rely on any assumptions that may appear due to bugs.

Difference in Null and Empty String

Hi,
I have been wondering about the difference between Null and Empty String in Java. So I wrote a small program like this:
public class CompareEmptyAndNullString {
     public static void main(String args[]) {
          String sNull = null;
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               } else {
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This program throws Exception: java.lang.NullPointerException
     at practice.programs.CompareEmptyAndNullString.main(CompareEmptyAndNullString.java:10)
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Can anyone explain why this would happen ?
Thanks in Advance !!

JavaProwler wrote:
Saish,
Whether you do any of the following code, the JUnit Test always passes: I mean he NOT Sign doesnt make a difference ...
assert (! "".equals(null));
assert ("".equals(null));
You probably have assertions turned off. Note the the assert keyword has nothing to do with JUnit tests.
I think that older versions of JUnit, before assert was a language keyword (which started in 1.4 or 1.5), had a method called assert. Thus, if you have old-style JUnit tests, they might still compile, but the behavior is completely different from what it was in JUnit, and has nothing to do with JUnit at all.
If you turn assertions on (-ea flag in the JVM command line, I think), the second one will throw AssertionError.

Differnce between null string and an empty string??

what is the major difference between null string and an empty string??
I wrote the following simple program and I could see some different output.
Other than that, any other differences that we should pay attention to???
C:\>java TestCode
Hello
nullHello
public class TestCode
     public static void main(String[] s)
     {     String s1 = "";
          String s2 = null;
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          System.out.println(s2 + "Hello");
}

There's a big difference between the two. A null String isn't pointing to an object, but an empty String is. For example, this is perfectly fine:
public class TestCode
    public static void main(String[] args)
        String s = "";
        System.out.println(s.length());
} It prints out 0 for the length of the String, just as it should. But this code will give you a NullPointerException:
public class TestCode
    public static void main(String[] args)
        String s = null;
        System.out.println(s.length());
} Since s isn't pointing to anything, you can't call its methods.

What is difference between Null String and Empty String ?

Hi
Just i have little confusion that the difference bet'n NULL String and Empty String ..
Please clear my doubte.
Thankx

For the same reason I think it's okay to say "null
String" and "empty String "as long as you know they
really mean "null String reference" and "empty String
object" respectively. Crap. It's only okay to say that as long as *the one you're talking to" knows what it really means. Whether you know it or not is absolutely irrelevant. And there is hardly any ambiguity about the effects that a statement like "assign an object to a reference" brings. "Null String" differs in that way.

Difference between null string and empty string??

what is the major difference between null string and an empty string??
I wrote the following simple program and I could see some different output.
Other than that, any other differences that we should pay attention to???
C:\>java TestCode
Hello
nullHello
public class TestCode
     public static void main(String[] s)
     {     String s1 = "";
          String s2 = null;
          System.out.println(s1 + "Hello");
          System.out.println(s2 + "Hello");
}

The difference is that an empty String is just empty but a null String has no value (i.e. it is not instantiated) this has signifigance since all Strings are objects.

VARCHAR2:: How to differnciate between NULL and empty string '' ?

Hello to all,
I'm looking for a possibility to differnciate between NULL and empty string '' in column of type VARCHAR2.
I have an application relying on that there is a difference between NULL and ''.
Is it possible to configure ORACLE in some way ?
Thanx in advance,
Thomas

try check if a varchar variable has an empty string
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DECLARE
v_test VARCHAR2(10);
BEGIN
v_test := '';
DBMS_OUTPUT.put_line(LENGTH(v_test));
v_test := NULL;
DBMS_OUTPUT.put_line(LENGTH(v_test));
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NULL vs. Empty String

I am new to ORACLE, moving over from MS SQL Server. Is it true that you cannot enter an empty string into a NOT NULL VARCHAR2?
I am trying to convert data from an existing DB and I NEED to be able to have an empty string as much of the code base is using this to validate data (vs. a NULL). Is there any solution at all for this problem? I really do not want to keep my existing DB running but there is too much time involved converting code.
Thanks, In Advance

Bryna,
In Oracle database, Oracle treats NULL and empty string
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Thanks
Martha

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Hi, I have this problem:
PreparedStatement bookedQtyPS = null;
String qry="SELECT * from djwsearch where djwitem=?;
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if(item.equals(""){ //item is an empty String
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}else{
bookedQtyPS.setString(1,item);
My problem is that I need to set space insteadOf empty String, but I think that I can not use PreparedStatement to do this. I have performance problems (my query is much more complicated than this one) so I choose PreparedStatement and not Statement.
How can I do? Is this bug solved using PreparedStatement?
Thanks.

you can do it with the help of PreparedStatement.
Here the type of field(djwitem) and setmethod is should be match..i mean if the type of ur field is String then you need to use the setSting method.
you can do one thing specify one string variable.
String space=" ";
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What is the difference between string constant which does not contain any value and the Empty string constant?
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Please Reply
prabhakant
Regards
Prabhakant Patil

Readability.
Functionally, they are the same. From a coding standpoint, the Empty String Constant is unambiguous.
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