JAVA
It is a programming language which is platform independent and support to open source platform, means code remains the same and you can run that code on any platform, java has virtual machine which is called JVM(JAVA virtual machine). Follow OOPS concepts.
Java was Developed by Oracle corporation and Designed by Sun Microsystems and James Gosling.
Java itself is a programming language having Advantages like distributed, secure, robust and multithreaded.
If we talk about designing: in java so to creating a simple control like button also take a lot of programming for developer.
Architecture: Java support connected architecture. Since java is multiplatform so it is a set of framework classes is limited to what is available on all platforms
.NET
It is a programming language which is platform dependent but language independent i.e. application written in any programming language can be converted into another language supported by framework(supported languages are VB.NET, C#.NET, J#.NET etc.). Also follow OOPS concepts. NET has no direct support for open source platform.
.NET was Developed by Microsoft to allow programmers to build dynamic application.
.net is a framework or simply a platform of presently 43 programming languages. Advantages like Consistent programming, easy deployment and maintenance of an application , direct support for security.
If we talk about designing in .NET provide more friendliness while designing any webpage or form because u can easy drag and drop the control which is not at all mind teasing process, developer can concentrate on logic and other security issues.
Architecture: .NET support disconnected architecture. .NET has a set of all the classes available on Microsoft platform.