Doubt in Hashmap key

Hi All,
I have got few long in HashMap as key. So in my code I wrote
long temp= Long.parseLong((String)tempmap.get(key)But at this time Iam getting number format exception but when I do
long temp= String.valueOf(tempmap.get(key))it works fine.The above is a pseudo code and not right way of extracting key-value from hashmap. My question as hashmap key is an object
and casting it to String and then Long.parseLong fails but String.valueOf succeeds why?
How both treat objects differently.
Thanks for the advice in advance

My actual code was
Map.Entry ent=(Map.Entry)itr.next();
Long.parseLong(String.valueOf(ent.getKey()))
The key is a long. I just wrote a pseudo code and not exact code as my doubt why when I do
Map.Entry ent=(Map.Entry)itr.next();
Long.parseLong((String)(ent.getKey())) it fails but the first code gives results.So how String casting and String.valueOf treats object.

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Hi BalusC,
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jsp:
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Problem using dynamic variable as HashMap key

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Basic doubt about Primary Keys/Foreign Keys in Oracle Tables

Hi,
I have a doubt whether Primary Keys/Foreign Keys are allowed in Oracle or not. I have been informed that Oracle does not encourage having Primary Keys/Foreign keys in its database tables. Instead it urges users to have unique constraints on the requisite columns.
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FYI,
There is seprate forum for Core Sql quieries
PL/SQL
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Hello,
It's very possible I'm missing some things here, but I've attempted to review your code.
Let me just define the specs of the code as I see them:
Method useZone accepts String input, which is "supposed" to be the key to a hashmap.
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The value is of type Integer.
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Map<String, Integer> hm = new HashMap<String, Integer>();And you can get rid of the casts. I would also suggest renaming the hashmap to something that describes what it holds, rather than it's object type. Maybe something like timeZoneMap - or offsetMap. I would also consider renaming "use" to something that describes the data it might hold, instead of something that describes the workflow.
Variable naming is very difficult! I would suggest renaming all of your variables, but I think those are the only ones I kept!
Edited by: Adam_Schaible on Nov 28, 2007 12:09 PM

Doubt on hashmap

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That's right. After the loop you'll only have two
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Strings as hashmap keys

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that is ...
image is read in from a file
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Make sense?

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Doubt with PRIMARY KEY in sql!

Dear friends,
Can you please explain me this scenario's problems
create table a ( eno number);
alter table a add( eno1 number primary key);
alter table a drop primary key;when i describe the table still the column eno1 is showing as NOT NULL. and i cannot modify it as NULL also by sayin
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Regards,
Manoj

bluefrog --
Did you repeat the OP's test case exactly? Here is both yours and the OP's on an 11.2.0.2 system and they behave differently.
SQL> create table a(eno number primary key);
Table created.
SQL> desc a;
Name                                                                                      Null?    Type
ENO                                                                                       NOT NULL NUMBER
SQL> alter table a drop primary key;
Table altered.
SQL> desc a;
Name                                                                                      Null?    Type
ENO                                                                                                NUMBER
SQL> select * from v$version;
BANNER
Oracle Database 11g Enterprise Edition Release 11.2.0.2.0 - 64bit Production
PL/SQL Release 11.2.0.2.0 - Production
CORE    11.2.0.2.0      Production
TNS for Solaris: Version 11.2.0.2.0 - Production
NLSRTL Version 11.2.0.2.0 - Production
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Table dropped.
SQL> create table a(eno number);
Table created.
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Table altered.
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Name                                                                                      Null?    Type
ENO                                                                                                NUMBER
ENO1                                                                                      NOT NULL NUMBER
SQL> alter table a drop primary key;
Table altered.
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Name                                                                                      Null?    Type
ENO                                                                                                NUMBER
ENO1                                                                                      NOT NULL NUMBER
SQL>

Doubt with primary key

How can we update the primary key column in the master table and referential integrity in the child table ,
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ERROR at line 1:
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Hi,
Why don't you just disable the foreign key constraint?
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Table created.
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1 row updated.
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         2Cheers
Legatti

Doubt in hashmap?

we may have many null keys in hashmap

But not "many", as the OP seems to be (?) asking...Yeah I tried to guess what the OP was asking and picked a question for him / her :o)
If the OP had been meaning whether it is possible to have multiple null keys simultaneously in the same map, then obviously the answer would be no.
Hopefully the OP didn't mean that though - as thats just crazy :o)

How to get the value in a hashmap with a key of expression "123-456"?

Hi all,
I new to java and having a problem with getting values from a hashmap.here is the code which i wrote
Map map = new HashMap();
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boolean b = map.get(String.valueOf(m) + "-" + String.valueOf(n));Can someone help me how to pass this expression as key in the hashamp

Hi corlettk,
Thanks for your reply. I have defined my map as Map<String, Boolean> selectedIds = new HashMap<String, Boolean>();
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How to get first item of hashMap w/out knowing the key

Hi
can someone tell me if there is a way to get first item from a hashMap when you dont know what the key is. as the get method expects a defined 'key'
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I am using struts 2 UI <s:radio> tag. this tag takes a hashmap and creates radio maps. it has a 'value' attribute and if something is passed to this attribute then that radio button is checked by default. the list that contains radio buttons is created dynamically so i dont know what is actually in the hashMap key's. but i do know that key's are string.
so just wondering if there is a way to get first item from a hashmap without knowing the key...

thanks for the quick reply.
posted in java forums because thought it was a java API/workaround question. gave a little history because i didnt want people to start questioning my use of HashMap for this purpose..
anywhose..i've found a workaround.
If someone has a similar problem:
as the hashmap is being populated dynamically....set a String member of class to contain the first key thats being put in the hashmap. then have struts tag pick up that value.
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Requirement for object key for HashMap

Hi,
I would like to put the object to HashMap keyed by my own object. what is the requirement for the class to be key? I have a method boolean equals(Object o) defined in the key class, My key is composed by 2 ids, so in the equals method I compared the 2 ids. but it seems can't get the value out. Please help. Thanks

How do I supposed to do the hashCode? If myKey1.equals(myKey2) returns true, then myKey1.hashCode() must return the same value as myKey2.hashCode(). One consequence of this is that if something is not used to compuate equals(), then it must not be used to compute hashCode(). (Note that the reverse is not true. That is, if two objects are not equal, they can still return the same value from hashCode(), and hence, if some data is used for equals() it may still be left out of hashCode().)
You want hashCode to be 1) quick & easy to compute and 2) "well distributed" or "mostly unique. If you know how hashcodes are used (in the general sense, not just the Java hashCode() method) then you should understand why those properties are desirable. If not, just ask.
The most common approach is to use some subset of the object's fields in computing the hashCode. If you have a Person object with lastName, firstName, birthdate, height, weight, address, phone number, you probably wouldn't use all those fields. You could just lastName, or maybe a combination of lastName and firstName.
One generally combines multiple pieces by taking XORing (the "^") operator the individual pieces (for primitives) or their hashcodes (for objects). For example, in the Person example: public int hashCode() {
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Doubt in Hashmap key

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