some questions about java

题目

some questions about java
What are the two main component programs in the Sun Java Development Kit?What does each of them do?
What is the difference between the filename ending with .java and the file name ending with .class?
What is Dr Java?What kinds of things can we do with Dr Java?In Our class we can use Netbeans,Eclipse,InteliJ,Jbuilder or other tools.So you can choose the tool by yourself and Dr Java can be any developing tool.
Why is it easier to use Dr Java with the Sun JDK than to use the Sun JDK by itself?
chinese is fine as well .
please lable the number of the question after your answer.

答案

The first question I don't know how to give U an answer..I just understand them, but can not explain them.The file which are ended with .class have been ran through the file javac.exe which in the JD...