Top 20 frequently used java packages

i saw API documentation from java.sun.com
there are about 200 packages
can you mention top 20 packages which are frequently used and most important

Difficult to say which is most important . . .

Some of the more frequently used:

java.lang Used all the time. String may be the most frequently used class of all

javax.swing

java.awt.event

java.util

java.io

In beginners' code, 99% of the API classes used will probably come from those packages.

Avoid packages whose names start with com.sun or similar; those classes might be changed in the future.
Don't go through packages reading all the classes, but look for the classes you think you might need and look at their API documentation.

It's difficult to answer that question, because what packages you need depends on what kind of software you are writing. For example, if you are writing a desktop application or an applet, then you most likely use the Swing and AWT packages (javax.swing and java.awt), but if you're writing server-side software that doesn't have a GUI then you don't need those.

Ofcourse, the classes in java.lang and java.util are the most used packages from the standard Java API.

Originally posted by Campbell Ritchie:
String may be the most frequently used class of all

This is true of every application I've run through a profiler (mostly web apps). I seem to remember that second place went to HashTable, presumably used by the JVM or J2EE for mapping purposes.

Depending on what you're doing, I might add java.math and java.text to the list. But as already mentioned, a beginner is not going to stray much outside of java.lang and java.util, and the list of other packages you're likely to use is a lot smaller than you think. So don't let the API intimidate you.

I think these are probably my top, well, 23:

java.lang
java.util
java.io
java.util.regex
java.text
java.sql
java.net
java.util.concurrent
java.util.concurrent.locks
java.util.concurrent.atomic
javax.servlet
javax.servlet.http
java.lang.reflect
java.nio
java.nio.channels
java.nio.charset
javax.swing
java.awt
java.awt.event
org.xml.sax
org.w3c.dom
javax.xml.parsers
javax.naming

I think the first two will be true for eveyone, and after that it really depends on what sort of jobs you get hired to do. As a beginner, I'd just focus on the first two.
[ December 21, 2007: Message edited by: Jim Yingst ]

Thank you
it was very useful