why java is popular

Any technology  if know the popularity of that our  learning interest will increase right  that's  below points:)

1.Simple grammar - Java has a very simple grammar familiar to anyone with experience in C and C++, which must be 99.9% of programmers. 

2.Portability - Platform independence (Write Once Run Anywhere). Briefly, once you write the application, it can run in many different environments.

3.Speed - The latest JIT compilers for Suns JVM approach the speed of C/C++ code, and in some memory allocation intensive circumstances, exceed it. (Too bad Ruby, Python, Perl, and Squeak don't even come close)
4.Standard APIs - You can happily write your code knowing that the standard java.* libraries will be waiting on the client for it, assuming a recent enough version of Java is installed.huge standard library. Lots of third-party libraries.
5.GarbageCollection - the programmer doesn't have to worry about memory (most of the time)
6.VM - see WhyAreVirtualMachinesGreat
7.interface vs. class
8.CheckedExceptions (some people hate this, but its optional) (some ppl love it)
9.singly rooted class hierarchy (the reason that lack of templates isn't a killer)
10.no OperatorOverloading
11.reflection
12.Inherent support for dynamic linking and loading.
13.Guarantees of binary compatibility w.r.t. changes to linked code.
14.Security model for restricted execution
9.singly rooted class hierarchy (the reason that lack of templates isn't a killer)
10.no OperatorOverloading
11.reflection
12.Inherent support for dynamic linking and loading.
13.Guarantees of binary compatibility w.r.t. changes to linked code.
14.Security model for restricted execution