What are the unique features of Java?

In Java, everything is an object. This way, true encapsulation is achieved.  Java also has stronger enumerated types and the ability to synchronize threads. 

1. Java is simpleJava is an elegant language combined with a powerful and well-designed set of APIs. Programmers enjoy programming in Java and are usually amazed at how quickly they can get results with it. Studies have consistently shown that switching to Java increases programmer efficiency. Because Java is a simple and elegant language with a well-designed, intuitive set of APIs, programmers write better code with fewer bugs than for other platforms, again reducing development time.
2. Java is Platform Independent Java Provides the facility of cross-platform programs (known as "Write once -Run any where") by compiling in intermediate code known as bytecode. this bytecode can be interpreted on any system which have Java Virtual Machine(JVM).
3. Java is Secure Java is designed to be secure in a networked environment. The Java run-time environment uses a bytecode verification process to ensure that code loaded over the network does not violate Java security constraints.
4. Java is Robust Java has the strong memory allocation and automatic garbage collection mechanism. It carries out type checking at both compile and runtime making sure that every data structure has been clearly defined and typed. compiler checks the program for any error and interpreter checks any run time error that every data structure is clearly defined and typed. Java manages the memory automatically by using an automatic garbage collector. all the above features makes Java language robust.
5. Java runs in high performance Although Java is an interpreted language, it was designed to support “just-in-time” compilers, which converts Java byte codes to native machine instructions on the fly. Using sophisticated JIT compilers, Java programs can execute at speeds comparable to the speeds of native C and C++ applications.
6. Java is multithreaded Java supports multiple threads of execution (a.k.a., lightweight processes), including a set of synchronization primitives. This makes programming with threads much easier.

Java is a100% pure object oriented programming language,,

beeing a virtual machine ;)

JAVA is SIMPLE ,OBJECT ORIENTENTED,PLATFORM INDEPENDENT,SECURE.

I'd add one more point to what Mohamed Rami Assi  mentioned above is that Java is a widely used language that it's easy to find active communities and resources through out the internet to support you and give you best practices, in addition to Oracle's free tutorial and the perfectly designed API documentation...just to name few :)