Java Glossary
Last updated by Roedy Green
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U
- UDP
- User Datagram Protocol. This protocol is
build on top of IP, and allows sending datagrams -- messages of
arbitrary length (broken into packets). UDP makes no provision
for checking that a message was received or retransmitting it.
See IP, TCP/IP.
-
UML
- UML stands for Universal Modeling Language. It
is a modeling technique designed by Grady Booch, Ivar Jacobson, and James
Rumbauch of Rational Rose. It is used for OOAD (Object Oriented
Analysis and Design) It is supported by a broad base of
industry-leading companies which, arguably, merges the best of the various
notations into one single notation style. It is rapidly being supported by
many tool vendors, but the primary drive comes from Rational Rose.
UML CASE designers written in 100% Java include:
- Unicode
- A 16-bit character encoding used in Java. Sometimes called UCS or ISO
10646. Unicode allows Java to handle international characters for most of
the world's living languages, including airport symbolic icon, APL,
Arabic, Armenian, Bengali, Bopomofo, Chinese (via unified Han), Cyrillic,
English, Georgian, Greek, Gujarati, Gurmukhi, Hebrew, Hindi (Devanagari),n
Japanese (Kanji, Hiragana and Katakana via unified Han), Kannada, Korean
(Hangul via unified Han), Lao, mathematics, Maylayalam, Oriya, Tai, Tamil,
Telugu and Tibetan. Unicode will make it much easier for non-English
speaking programmers to write programs for English speaking users and vice
versa. DownloadWord For Windows
document giving the full Unicode character set with Java, HTML and
Postscript encodings. Nic Fulton has written an Applet
that can display all 64 thousand Unicode characters including the
Chinese/Korean Han. How many of them actually display on your
screen depends on the font handling ability of your browser and operating
system, and which fonts you have installed. In Java programs, intractable
Unicode characters are represented in the form '\uffff', with four hex
digits. Ordinary characters like 'A' are actually 16-bit Unicode too. See
literal.
- unmaintainable
code
- One of my most popular essays is a tongue in cheek How To Write Unmaintainable Code. Perhaps you would
like to submit additions to it.
- unsigned
- in Java bytes, shorts, ints and longs are all considered signed. The
only unsigned type is the 16-bit char. To use the sign bit as an
additional data bit you have to promote to the next bigger data type with
sign extension then mask off the high order bits. i.e. To get the effect
of an 8-bit unsigned:
byte b;
...
int i = b && 0xff;
To get the effect of effect of a 16-bit unsigned use char.
To get the effect of a 32-bit unsigned:
int i;
...
long l = i && 0xffffffffL;
- upcasting
- Doing a cast from a derived class to a more general base
class. The cast is nugatory, which is the 50 cent way of saying
it is not necessary but it won't hurt. e.g. Dog d = (Dog)
aDalmatian; Most people will stare blankly at you if you use
the word upcast. Just use cast. See cast,
downcasting.
- update
- Clear the area for the component to the background colour by doing a
fillrect then paint. update calls paint directly.
update routines are often overridden to eliminate the fillrect
which will reduce flicker. See paint, repaint.
- update
- To install a more recent version of a program. The newer version is
free. See upgrade.
- upgrade
- To install a more recent version of a program. The newer version is
not free. See update.
- upload
- Send a file. See download. As a memory aid, think of the BBS you are
communicating with as being a regal personage perched in a castle high UP
on a hill. In the case one person calls another, the caller uploads
(sends) and downloads (receives) files.
- URI
- Uniform Resource Indentifier, formerly called
URLs. URIs are slightly more general. e.g. http://www.hans.org/index.html.
It gives the site name and the document name within that site. See URN,
URL.
- URL
- Uniform Resource Locator, e.g.
http://www.hans.org/index.html. It gives the site name and the document
name within that site. See URN, URI.
- URN
- Uniform Resource Number. These will eventually replace URLs. A URN
will automatically find the file you want from the closest or least busy
server where the file is mirrored/cached. You can think of a URN as
analogous to extending the ISBN book cataloging system to cover all the
web pages as well. If you think about how paper books are distributed
through wholesalers, bookstores and libraries, that will give you a
metaphorical framework with which to think about URN caching. It works on
much the same economic principles. The main difference is that with a URN,
it is very cheap to Xerox a whole "book".
- USENET
- A method of broadcasting messages to everyone who is interested in a
given narrow topic. There are currently about 4000 topics. Only one copy
of the message is sent to each computer supporting people interested in
that topic. In contrast, a mail list would send individual copies to each
user on the list. Usenet topics are for large global, public, communities
of interested users. Mail lists are for smaller private groups. Sometimes
called "newsgroups".
- UTF
- UTF is not intended to be human-readable. It is a
compact binary-encoded form of Unicode that uses a mixture of 8,
16 and 24-bit codes. Strings are stored as a 16-bit big-endian
length count followed by a 7-bit ASCII string. Not null
terminated. "ABC" == 0x0003414243. Non-ASCII-7 chars
use multibyte encodings with first byte having the high bit on.
UTF is an external format. UTF strings are interconverted to
ordinary Strings during I/O by readUTF and writeUTF. Unicode-2
supports even 32 bit characters, and UTF has been extended to
handle them as well.
Unicode |
UTF |
bytes required to represent the
character |
00000000 0xxxxxxx |
0xxxxxxx |
1 |
00000yyy yyxxxxxx |
110yyyyy 10xxxxxx |
2 |
zzzzyyyy yyxxxxxx |
1110zzzz 10yyyyyy 10xxxxxx |
3 |
- UUCP
- Unix To Unix Command Processor/Protocol.
This is store and forward protocol for transferring files over Internet.
This is how USENET traffic propagates from node to node.
- UUENCODE
- Non-Transparent channels don't simply pass all characters through
unmolested. They treat some of the characters as control characters --
commands. In order to send arbitrary text down such channels, you need to
convert the special characters into vanilla ones that can get through
safely. One technique of converting a file into vanilla before sending is
called UUENCODE. see also MIME transparent.