JAVA Interpreted and compile

• Programming languages are classifies as
• Higher Level Language Ex. C++ , Java
• Middle Level Languages Ex. C
• Low Level Language  Ex Assembly
• finally the lowest level as the Machine Language.

A compiler is a program which converts a program from one level of language to another. Example conversion of C++ program into machine code.
The java compiler is a convert’s high level java code into bytecode (which is also a type of machine code).
A interpreter is a program which converts a program at one level to another programming language at  the same level. Example conversion of Java program into C++
In Java , the Just In Time Code generator converts the bytecode into the native machine code which are at the same programming levels.
Hence java is both compiled as well as interpreted language.

why is Java slow ?

The two main reasons behind the slowness of Java are
Dynamic Linking = Unlike C, linking is done at run-time , every time the program is run in Java.
Run-time Interpreter =  The conversion of byte code into native machine code is done at run-time in Java which furthers slows down the speed However, the latest version of Java have addressed the performance bottlenecks to a great extent.

For More Details Visit
http://www.javatutorialhub.com/java-virtual-machine-jvm.html