What is .NET framework in java ?

The question should be reformatted. Let me give you a brief:

.NET Framework and Java are two different platforms allowing the applications developed using them to run on different operating systems. Both uses the same technique by transferring the code written into an intermediate language which can be translated by their core components.

For example:

1. Java:

Java Code -> Byte Code -> Interpreted by JRE (Java Run-Time)

2. .NET:

Any .NET language -> MSIL (Microsoft Intermediate Language) -> Interpreted by CLR (Common Language Run-Time)

The ability to run on different operating systems is called interoperability which is supported by Java more than .NET. .NET is basically supported by Microsoft Operating Systems only officially; but it is supported by Android, most Linux distributions, BSD, OS X, Windows, Solaris, and even some game consoles such as PlayStation3, Wii, and Xbox360 using Mono which is the .NET Framework couterpart.

Why it need to have? Both .Net and Java has their own frameworks (.Net Framework and JVM respectively) and have their indepedent memory management, languages, managed code and has JIT support etc. 

i got your question so i will answer you in your way, the .net  framework in java is JVM :)

I think your question is what is the connection between java and .Net.

well, Java and .net don't output binary files instead they output assemblies and archives written in intermediate languages which can be recompiled to the machine language on execution time using a pre-installed framework (This is Write once execute any where).

But the main defference is that .net can only run on Microsoft Windows, where java can run on any platform like Mac and Linux