javap

Java source compiled to into an intermediate bytecode (i.e .class file). Most of us have never seen it before. One way to view the byte code is to compile your class and then open the .class file in a hex editor and translate the bytecodes by referring to the virtual machine specification. JavaP convert the byte codes into human-readabl format.
tryout

javap java.io.DataInputStream
This helps very much for students. Because they don't get API or development IDE at the exam time. There is no way to check available API option with notepad and command prompt. Hope this will help.

tryout
javap -c JavapApplication

javap -classpath Specify where to find user class files
javap -extdirs Override location of installed extensions
javap -help Print this usage message
javap -J Pass directly to the runtime system
javap -l Print line number and local variable tables
javap -public Show only public classes and members
javap -protected Show protected/public classes and members
javap -package Show package/protected/public classes and members (default)
javap -private Show all classes and members
javap -s Print internal type signatures
javap -bootclasspath Override location of class files loaded by the bootstrap class loader
javap -verbose Print stack size, number of locals and args for methods. If verifying, print reasons

History of java

1991	The Green Project Begins MS DOS is the dominant operating system Cell phones weigh half a pound "Biosphere 2" project begins
1992	"Oak" is the language *7 Debuts "Duke" is featured in the Interface Johnny Carson signs off "The Tonight Show" on NBC
1993	The Green Project becomes FirstPerson Mosaic v1.0 is released "Cheers" ends an 11-year run
1994	WebRunner released — the first browser that supports moving objects and dynamic executable content The Apple QuickTake 100, the first consumer digital camera, goes on sale for less than $1,000 "Friends" debuts on NBC
1995	Java technology released to a select group on the Web site wicked.neato.org The San Jose Mercury News runs a front-page article about Java technology Name changed from "Oak" to "Java" Announced at Sun World -- Java technology is officially born
1996	The first JavaOne Developer Conference JDKtm 1.0 software is released Chess computer Deep Blue defeats Garry Kasparov for the first time "Dolly" the first cloned sheep is born
1997	Over 220,000 downloads of JDK 1.1 software occur in just three weeks JavaOne draws 8,000 attendees, becoming the world's largest developer conference Java Card 2.0 platform is unveiled 43% of U.S. families own a computer
1998	JDK 1.1 release downloads top 2 million Visa launches world's first smart card based on Java Card technology The Java Community Process (JCP) program formalized "Who Wants to Be a Millionaire?" premieres in the U.K
1999	Java 2 platform source code is released JavaOne draws 20,000 J2EE beta software is released "Star Wars Episode I: The Phantom Menace" released
2000	Over 400 Java User Groups are established worldwide Java Developer Connection program tops 1.5 million members Steve Jobs joins Scott McNealy on stage at JavaOne to announce a major commitment by Apple in support of Java technology Heavy Metal band Metallica sues Napster for copyright violations
2001	First international JavaOne conference in Yokohama Japan Over 1 million downloads of the Java Platform, Enterprise Edition (Java EE) SDK Google Inc. PageRank search algorithm patent awarded "The Lord of the Rings: The Fellowship of the Ring" is released
2002	J2EE SDK downloads reach 2 million 78% of executives view J2EE technology as the most effective platform for building and deploying Web services The Euro is introduced "The Osbournes" becomes a surprise hit on MTV
2003	Java technology runs in almost 550 million desktops Almost 75% of professional developers use Java programming language as their primary development language Commercial Voice-Over-Internet (VoiP) phone service begins "The Da Vinci Code" is published
2004	Java 2 Platform, Standard Edition 5 (Project Tiger) is released The Java technology-powered Mars Rover (Spirit) touches down on Mars Sun Java Studio Creator is launched
2005	Java technology celebrates its 10th birthday Approximately 4.5 million developers use Java technology Over 2.5 billion Java technology-enabled devices are available java.com bundles the Google Toolbar with the JRE download
2006	Rich Green announces at the JavaOne 2006 Conference that it's not a matter of when Sun will open source Java technology, but how. The NetBeans IDE 5.0 is released. Sun open-sourced Java EE components as the Glassfish Project to java.net. Java SE and ME initial components are released as open source. Pirates of the Caribbean: Dead Man's Chest is released.