Having access to the source code of the JDK is incredibly important and you can learn quite a lot! Within Eclipse, you may find the following screen on occasion. This example below shows an attempt to view the source for a particular class (the actual one below is not important). What matters is that you
Click on the "Attach Source..." button. You will be shown the following dialog box:
You must locate the file "src.zip" which is included within the full JDK release. Click on "External File..." and browse to the proper location on your computer (should be found in "C:\Program Files\Java\" area If you do not have a full JDK installation (let's say it is only a jre1.5.0.03 installation), you must go to the Javasoft web site to retrieve the full installation. This is why I advised you initially to download the J2SE full development environment.
Assuming you have been able to proceed, click on OK.
After a moment, the actual source code should appear within your code window.