HashMap Keys?

5 Message(s) by 5 Author(s) originally posted in java developer

From: kk_oop

Date: Thursday, July 01, 2004

Hi. I'm looking for advice on using key

1. <database> A value used to identify a {record} in a
	database, derived by applying some fixed function to the
	record.  The key is often simply one of the {fields} (a
	{column} if the database is considered as a table with records
	being rows, see "{key field}").  Alternatively the key may be
	obtained by applying some function, e.g. a {hash function}, to
	one or more of the fields.  The set of keys for all records
	forms an {index}.  Multiple indexes may be built for one
	database depending on how it is to be searched.

	2. <cryptography> A value which must be fed into the
	{algorithm} used to decode an encrypted message in order to
	reproduce the original {plain text}.  Some encryption schemes
	use the same (secret) key to encrypt and decrypt a message,
	but {public key encryption} uses a "private" (secret) key and
	a "public" key which is known by all parties.

	3. <hardware> An electromechanical {keyboard} button.

	(2003-07-04)

s for a HashMap.

Is it typical to just use a string

<programming> A sequence of {data} values, usually {bytes},
	which usually stand for {characters} (a "character string").
	The {mapping} between values and characters is determined by
	the {character set} which is itself specified implcitly or
	explicitly by the environment in which the string is being
	interpreted.

	The most common character set is {ASCII} but, since the late
	1990s, there has been increased interest in larger character
	sets such as {Unicode} where each character is represented by
	more than eight {bits}.

	Most programming languages consider strings (e.g.
	"124:shabooya:\n", "hello world") basically distinct from
	numbers which are typically stored in fixed-length {binary} or
	{floating-point} representation.

	A {bit string} is a sequence of {bits}.

	(1999-12-21)

as a key, e.g., "Item A", "Item B",
etc.? Or are other approaches better? Since the key is just an
Object, I thought there might be some other approach commonly used
that is more efficient/effective.

Thanks for any advice!

Ken

From: grisha

Date: Wednesday, July 14, 2004

Hi. I'm looking for advice on using keys for a HashMap.

It all depends on what you're trying to do, duh :). First of all, check out
how the HashMap works at all, the source

<language, programming> (Or "source", or rarely "source
	language") The form in which a computer program is written by
	the programmer.  Source code is written in some formal
	programming language which can be compiled automatically into
	{object code} or {machine code} or executed by an
	{interpreter}.

	(1995-01-05)

is available. See if you understand
the requirements

<programming> The first stage of software development which
	defines what the potential users want the system to do.  In
	modern methods these requirements should be testable, and will
	usually be traceable in later development stages.  A common
	feature of nearly all software is that the requirements change
	during its lifetime.

	See {software life-cycle}.

	(1995-11-11)

for equals() / hash

1. <character> {hash character}.

	2. <programming> {hash coding}.

	3. The preferred term for a {Perl} {associative array}.

	(1995-03-06)

Code(). See if you can follow why
Strings are common choice (well, also because it's just easy :). But maybe
that's not what you want. What problem are you trying to solve?

From: giffy_jif

Date: Friday, July 16, 2004

Is it typical to just use a string as a key, e.g., "Item A", "Item B",
etc.? Or are other approaches better? Since the key is just an
Object, I thought there might be some other approach commonly used
that is more efficient/effective.

Do not worry too much whether using String is more efficient (generally
it's bad to worry about optimization during implementation). You
should use whatever object

<object-oriented> In {object-oriented programming}, an
	instance of the data structure and behaviour defined by the
	object's {class}.  Each object has its own values for the
	{instance variables} of its class and can respond to the
	{methods} defined by its class.

	For example, an object of the "Point" class might have
	instance variables "x" and "y" and might respond to the "plot"
	method by drawing a dot on the screen at those coordinates.

	(2004-01-26)

which makes the best sense in your
situation. Note that Map keys must be *immutable*, otherwise the Map
may not work properly. Strings are immutable.

From: curtinsteve

Date: Thursday, July 22, 2004

wrote in message

In {object-oriented programming} sending a message to an
	{object} (to invoke a {method}) is equivalent to calling a
	{procedure} in traditional programming languages, except that
	the actual code executed may only be selected at run time
	depending on the {class} of the object.  Thus, in response to
	the message "drawSelf", the method code invoked would be
	different if the target object were a circle or a square.

	(1995-02-16)

Hi. I'm looking for advice on using keys for a HashMap.
Is it typical to just use a string as a key, e.g., "Item A", "Item B",
etc.? Or are other approaches better? Since the key is just an
Object, I thought there might be some other approach commonly used
that is more efficient/effective.
Thanks for any advice!
Ken

Hi Ken

I always use Strings as keys in a hash map and I've never
encountered problems in either effiency or effectiveness

Steve

From: Adam Maass

Date: Wednesday, July 20, 2005

wrote in message:

Is it typical to just use a string as a key, e.g., "Item A", "Item B",
etc.? Or are other approaches better? Since the key is just an
Object, I thought there might be some other approach commonly used
that is more efficient/effective.
Do not worry too much whether using String is more efficient (generally
it's bad to worry about optimization during implementation). You
should use whatever object which makes the best sense in your
situation. Note that Map keys must be *immutable*, otherwise the Map
may not work properly. Strings are immutable.

Not quite. Objects used as keys in a Map must not change while they are in
use as keys in a Map. Immutable objects never change once constructed, so
they meet this requirement.

-- Adam

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