Here are some major differences between Java and .Net from some website
Conceptually, Java is two things: the Java platform (runtime and APIs), and the Java language.
The purpose of the Java platform is to support applications written in the Java language and
compiled to Java bytecode. The ideal of Java has always been a single language on multiple platforms.
.NET also is two things: the .NET Framework (runtime and APIs), and the plethora of supported
programming languages. The purpose of the NET Framework is to support applications written
in any language and compiled to MSIL. The goal of .NET is a single platform shared by multiple language
The most obvious difference between the two platforms is the language. If you're writing
to the Java platform, you're writing code in Java.
.NET applications, on the other hand, can be written in any language that supports .NET.
The .NET Framework SDK ships with three languages: C#, Visual Basic .NET, and Jscript .NET.
Third party languages include COBOL, Eiffel, Perl, Python, Pascal, and many others.
There currently are over 20 languages that support .NET. And because they all target the
Common Language Runtime, programs written in any of these languages can access objects
created by any of the other languages.
Hope this will help you.