The J2SE 1.5 is the advance version released by the sun.
They have made more addition in the existing J2SE1.4 in makeing Collection framework better.
Many additions for jdk1.5 than jdk1.4
For example :
1. import static
2. generic type
The base of JDK1.4 is reused with the JDK1.5
Addtition of generics, autoboxing and annotations etc..
For more information visit to :http://www.roseindia.net/java/http://www.roseindia.net/java/beginners/download_jdk.shtml