JDK 1.5 and JDK 1.6 are different Java versions that are available. JDK 1.5 is also known as a program that was released back in the year 2004. JDK is very effective in offering support to generics so that the documentation will show that it is very compatible. There are various things that you can do with the 1.5, such as being able to do enumerations.
The main difference of this with the 1.6 is that you can use the 1.6 and expect that everything is going to be seamless and that everything will be executed without any problems. There are obviously some benefits that will occur when someone upgrades from 1.5 to 1.6.