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difference between hashtable and hashMap ?

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  difference between hashtable and hashMap ? Rishipal Singh <95rishipal@gmail.com> - 2014-08-23 23:03 -0700
    Re: difference between hashtable and hashMap ? Andreas Leitgeb <avl@auth.logic.tuwien.ac.at> - 2014-08-24 08:09 +0000
    Re: difference between hashtable and hashMap ? Josip Almasi <joe@vrspace.org> - 2014-08-24 11:41 +0200
    Re: difference between hashtable and hashMap ? Eric Sosman <esosman@comcast-dot-net.invalid> - 2014-08-24 08:13 -0400
      Re: difference between hashtable and hashMap ? Arne Vajhøj <arne@vajhoej.dk> - 2014-08-24 08:48 -0400
        Re: difference between hashtable and hashMap ? Eric Sosman <esosman@comcast-dot-net.invalid> - 2014-08-24 09:28 -0400
          Re: difference between hashtable and hashMap ? Arne Vajhøj <arne@vajhoej.dk> - 2014-08-24 14:31 -0400
            Re: difference between hashtable and hashMap ? Roedy Green <see_website@mindprod.com.invalid> - 2014-08-24 22:35 -0700
              Re: difference between hashtable and hashMap ? Arne Vajhøj <arne@vajhoej.dk> - 2014-08-25 20:41 -0400
              Re: difference between hashtable and hashMap ? Jeff Higgins <jeff@invalid.invalid> - 2014-08-26 04:21 -0400
            Re: difference between hashtable and hashMap ? "Qu0ll" <Qu0llSixFour@gmail.com> - 2014-08-31 10:27 +1000
              Re: difference between hashtable and hashMap ? Arne Vajhøj <arne@vajhoej.dk> - 2014-09-07 22:10 -0400
                Re: difference between hashtable and hashMap ? "Qu0ll" <Qu0llSixFour@gmail.com> - 2014-09-08 13:41 +1000
    Re: difference between hashtable and hashMap ? Arne Vajhøj <arne@vajhoej.dk> - 2014-08-24 08:52 -0400
      OT: Re: difference between hashtable and hashMap ? Wayne <nospam@all.invalid> - 2014-08-24 18:04 -0400
    Re: difference between hashtable and hashMap ? Roedy Green <see_website@mindprod.com.invalid> - 2014-08-24 22:36 -0700
    Re: difference between hashtable and hashMap ? Brixomatic <brixomatic@yahoo.com> - 2014-08-30 14:07 +0200
      Re: difference between hashtable and hashMap ? Eric Sosman <esosman@comcast-dot-net.invalid> - 2014-08-30 16:39 -0400
        Re: difference between hashtable and hashMap ? Brixomatic <brixomatic@yahoo.com> - 2014-08-31 09:42 +0200

#29830 — difference between hashtable and hashMap ?

what is difference between hashtable and hashMap ;
 please explain with examples

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#29831

Rishipal Singh <95rishipal@gmail.com> wrote:
> what is difference between hashtable and hashMap ;
>  please explain with examples

HashTable is OLD - don't use it for new code.

(same as Enumeration and Vector)

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#29833

On 08/24/2014 08:03 AM, Rishipal Singh wrote:
> what is difference between hashtable and hashMap ;
>   please explain with examples

Hashtable is synchronized, and HashMap is not.
However, Hashtable's iterators are not synchronized, meaning it's rather 
useless - use ConcurrentHashMap instead.
Google ConcurrentHashMap examples.

Regards...

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#29835

On 8/24/2014 2:03 AM, Rishipal Singh wrote:
> what is difference between hashtable and hashMap ;
>   please explain with examples

     If by "hashtable" you actually mean "HashTable", the latter is
probably the class "java.util.HashTable", a key-to-value map that
has been around since the very first versions of Java.

     If by "hashMap" you actually mean "HashMap", the latter is
probably the class "java.util.HashMap", another key-to-value map
of more recent (Java 1.2, 1998) vintage.

     Both are used in similar ways: You can add and remove key/value
pairs, offer a key and retrieve its associated value, change the
value associated with a key, iterate over all the keys, all the
values, or all the pairs, and so on.  There are differences in
detail, most notably that HashTable methods are "synchronized"
while HashMap methods are not, but the two are broadly similar.

     Prefer HashMap unless you have a compelling reason to choose
HashTable instead -- for example, if you're using an old API that
specifically requires HashTable, you have no choice and must use
one.  But for new work, choose HashMap instead.  Also, if your
classes expose a key/value map to their clients, prefer to expose
it as a Map even if you actually use HashMap internally; that way,
you can change to a different kind of map later on (if that seems
a good idea) without disturbing your clients.


-- 
esosman@comcast-dot-net.invalid

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#29836

On 8/24/2014 8:13 AM, Eric Sosman wrote:
> On 8/24/2014 2:03 AM, Rishipal Singh wrote:
>> what is difference between hashtable and hashMap ;
>>   please explain with examples
>
>      If by "hashtable" you actually mean "HashTable", the latter is
> probably the class "java.util.HashTable",

Never heard of that one ...

>                                          a key-to-value map that
> has been around since the very first versions of Java.

If you ignore case then there is such a class ...

:-)

Arne

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#29838

On 8/24/2014 8:48 AM, Arne Vajhøj wrote:
> On 8/24/2014 8:13 AM, Eric Sosman wrote:
>> On 8/24/2014 2:03 AM, Rishipal Singh wrote:
>>> what is difference between hashtable and hashMap ;
>>>   please explain with examples
>>
>>      If by "hashtable" you actually mean "HashTable", the latter is
>> probably the class "java.util.HashTable",
>
> Never heard of that one ...

     <facepalm>"java.util.Hashtable", of course.</facepalm>

-- 
esosman@comcast-dot-net.invalid

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#29840

On 8/24/2014 9:28 AM, Eric Sosman wrote:
> On 8/24/2014 8:48 AM, Arne Vajhøj wrote:
>> On 8/24/2014 8:13 AM, Eric Sosman wrote:
>>> On 8/24/2014 2:03 AM, Rishipal Singh wrote:
>>>> what is difference between hashtable and hashMap ;
>>>>   please explain with examples
>>>
>>>      If by "hashtable" you actually mean "HashTable", the latter is
>>> probably the class "java.util.HashTable",
>>
>> Never heard of that one ...
>
>      <facepalm>"java.util.Hashtable", of course.</facepalm>

Given that hash and table are two words (in English) then
I guess it should have been with capital T, but ...

Arne

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#29848

On Sun, 24 Aug 2014 14:31:51 -0400, Arne Vajhøj <arne@vajhoej.dk>
wrote, quoted or indirectly quoted someone who said :

>
>Given that hash and table are two words (in English) then
>I guess it should have been with capital T, but ...

This business of capital letters in the middle of words was unknown
until WordPerfect did it.  Now it is everywhere.
-- 
Roedy Green Canadian Mind Products http://mindprod.com
Errors using inadequate data are much less than those using no data at all. 
~ Charles Babbage (born: 1791-12-26 died: 1871-10-18 at age: 79)

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#29854

On 8/25/2014 1:35 AM, Roedy Green wrote:
> On Sun, 24 Aug 2014 14:31:51 -0400, Arne Vajhøj <arne@vajhoej.dk>
> wrote, quoted or indirectly quoted someone who said :
>> Given that hash and table are two words (in English) then
>> I guess it should have been with capital T, but ...
>
> This business of capital letters in the middle of words was unknown
> until WordPerfect did it.  Now it is everywhere.

I would tend to consider Hashtable/HashTable for two words with
no space in between.

Where traditional Java convention is to capitalize both words.

Arne

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#29855

On 08/25/2014 01:35 AM, Roedy Green wrote:
> On Sun, 24 Aug 2014 14:31:51 -0400, Arne Vajhøj <arne@vajhoej.dk>
> wrote, quoted or indirectly quoted someone who said :
>
>>
>> Given that hash and table are two words (in English) then
>> I guess it should have been with capital T, but ...
>
> This business of capital letters in the middle of words was unknown
> until WordPerfect did it.  Now it is everywhere.
>
This article is asking for improvements.
<http://en.wikipedia.org/wiki/CamelCase#Computer_programming>

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#29876

"Arne Vajhøj"  wrote in message 
news:53fa2fa3$0$292$14726298@news.sunsite.dk...

> Given that hash and table are two words (in English) then
> I guess it should have been with capital T, but ...

I have always been fascinated by the naming of the System.out.println() 
method.

What naming rules does it follow other than "copy from C/C++ and Pascal"?

--
And loving it,

-Qu0ll (Rare, not extinct)
_________________________________________________
Qu0llSixFour@gmail.com
[Replace the "SixFour" with numbers to email me] 

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#29930

On 8/30/2014 8:27 PM, Qu0ll wrote:
> "Arne Vajhøj"  wrote in message
> news:53fa2fa3$0$292$14726298@news.sunsite.dk...
>
>> Given that hash and table are two words (in English) then
>> I guess it should have been with capital T, but ...
>
> I have always been fascinated by the naming of the System.out.println()
> method.
>
> What naming rules does it follow other than "copy from C/C++ and Pascal"?

None that I can think of.

It should have been printLine.

But I think it is a fair guess that this method may have been
implemented way before anybody had started thinking about
coding conventions.

Arne

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#29932

"Arne Vajhøj"  wrote in message 
news:540d102e$0$298$14726298@news.sunsite.dk...

>> I have always been fascinated by the naming of the System.out.println()
>> method.
>>
>> What naming rules does it follow other than "copy from C/C++ and Pascal"?
>
> None that I can think of.
>
>It should have been printLine.

I totally disagree - there's no "printing" of any kind happening here.

My choice would be "outputLine".

> But I think it is a fair guess that this method may have been
> implemented way before anybody had started thinking about
> coding conventions.

Probably, or at least when several different sets of conventions were 
floating around.

--
And loving it,

-Qu0ll (Rare, not extinct)
_________________________________________________
Qu0llSixFour@gmail.com
[Replace the "SixFour" with numbers to email me] 

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#29837

On 8/24/2014 2:03 AM, Rishipal Singh wrote:
> what is difference between hashtable and hashMap ;
>   please explain with examples

Hashtable - old, should not be used in new code if you can avoid it
HashMap - new, what you should use today

The reason for the two classes are historical/evolutionary.

Technically the main difference is that the methods in Hashtable
are synchronized while the methods in HashMap are not.

The benefit of single method calls being synchronized is
zero in single threaded context and often very small in
a multi-threaded context. And it do come with some overhead.
But in my opinion the false feeling of safety is a bigger problem
than the actual overhead.

Arne

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#29842 — OT: Re: difference between hashtable and hashMap ?

On 8/24/2014 8:52 AM, Arne Vajhøj wrote:
> On 8/24/2014 2:03 AM, Rishipal Singh wrote:
>> what is difference between hashtable and hashMap ;
>>   please explain with examples
> 
> Hashtable - old, should not be used in new code if you can avoid it
> HashMap - new, what you should use today
> 
> The reason for the two classes are historical/evolutionary.
> 
> Technically the main difference is that the methods in Hashtable
> are synchronized while the methods in HashMap are not.
> 
> The benefit of single method calls being synchronized is
> zero in single threaded context and often very small in
> a multi-threaded context. And it do come with some overhead.
> But in my opinion the false feeling of safety is a bigger problem
> than the actual overhead.
> 
> Arne
> 
> 

There is also synchronizedMap (created with java.util.Collections).
But if you care about current access, you are probably better of
with java.util.concurrent.ConcurrentHashMap.

-- 
Wayne

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#29849

On Sat, 23 Aug 2014 23:03:26 -0700 (PDT), Rishipal Singh
<95rishipal@gmail.com> wrote, quoted or indirectly quoted someone who
said :

>what is difference between hashtable and hashMap ;
> please explain with examples
 see http://mindprod.com/jgloss/hashtable.html
http://mindprod.com/jgloss/hashmap.html

This smells like homework.

http://mindprod.com/jgloss/homework.html
-- 
Roedy Green Canadian Mind Products http://mindprod.com
Errors using inadequate data are much less than those using no data at all. 
~ Charles Babbage (born: 1791-12-26 died: 1871-10-18 at age: 79)

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#29874

In article <a32f3a08-49ca-48dc-88c6-1b58aacbf1e5@googlegroups.com>, 
Rishipal Singh (95rishipal@gmail.com) says...
> 
> what is difference between hashtable and hashMap ;
>  please explain with examples

The HashTable is synchronized (not including the iterator), which is not 
needed usually. 
If you need synchronization you can use 
Map<K,V> synchMap = Collections.sychronizedMap(unsynchMap);
to wrap any map in a decorator/proxy map that adds synchronization (and 
is backed by the original you provided). One might think that with this 
the original HashTable is not needed anymore, but that's not entirely 
true.

The major advantage of java.util.HashTable to java.util.HashMap is that 
you can have a custom load factor with the HashTable, which might help 
you in improving the behavior in cases where you need to sacrifice some 
speed in favor of space. 
An increased load factor will slow the table down as hash collisions get 
more likely, but the table will not grow in size that fast, OTOH a lower 
load factor will make the table grow faster to provide more space for 
less hash collisions. 

Usually the load factor is a non issue and synchronization is not 
needed, which means that HashMap should be your standard map 
implementation. In rare cases, if you really need to fine tune a map, wi 
ch means you need some special property that HashMap doesn't supply 
(altering the load factor, iterating in the order in that the elements 
were added, removing duplicates and/or ordering according to a custom 
comparator stragety, lightly multithreaded access, heavy multithreaded 
access, values that become free for garbage collection if their keys are 
not referenced anymore, etc.) you might have a look at other Map 
implementations, such as HashTable, ConcurrentHashMap, TreeMap or 
WeakHashMap. But you should really know what you're doing there, which 
means (regarding your novice question), probably not yet.

Kind regards,
Wanja

-- 
..Alesi's problem was that the back of the car was jumping up and down 
dangerously - and I can assure you from having been teammate to 
Jean Alesi and knowing what kind of cars that he can pull up with, 
when Jean Alesi says that a car is dangerous - it is. [Jonathan Palmer]

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#29875

On 8/30/2014 8:07 AM, Brixomatic wrote:
> In article <a32f3a08-49ca-48dc-88c6-1b58aacbf1e5@googlegroups.com>,
> Rishipal Singh (95rishipal@gmail.com) says...
>>
>> what is difference between hashtable and hashMap ;
>>   please explain with examples
>
> The HashTable is synchronized (not including the iterator), which is not
> needed usually.

     It's "Hashtable", not "HashTable" (I made the same mistake, so
I can sympathize ...)

>[...]
> The major advantage of java.util.HashTable to java.util.HashMap is that
> you can have a custom load factor with the HashTable, which might help
> you in improving the behavior in cases where you need to sacrifice some
> speed in favor of space.

     Um, er, why do you think HashMap's load factor can't be customized?
Is the HashMap(int,float) constructor lying to us?

-- 
esosman@comcast-dot-net.invalid

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#29877

In article <lttcqr$1l4$1@dont-email.me>, Eric Sosman (esosman@comcast-
dot-net.invalid) says...

>      Um, er, why do you think HashMap's load factor can't be customized?
> Is the HashMap(int,float) constructor lying to us?

Dang! How could I miss that?
My bad.

Kind regards,
Wanja

-- 
..Alesi's problem was that the back of the car was jumping up and down 
dangerously - and I can assure you from having been teammate to 
Jean Alesi and knowing what kind of cars that he can pull up with, 
when Jean Alesi says that a car is dangerous - it is. [Jonathan Palmer]

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