Java Compiler - A Java compiler is a compiler for the Java programming language. The most common form of output from a Java compiler is Java class files containing platform-neutral Java bytecode. There exist also compilers emitting optimized native machine code for a particular hardware/operating system combination.
Most Java-to-bytecode compilers, Jikes being a well known exception, do virtually no optimization, leaving this until run time to be done by the JRE.
The Java Virtual Machine (JVM) loads the class files and either interprets the bytecode or just-in-time compiles it to machine code and then possibly optimizes it using dynamic compilation.
The very first Java compiler developed by Sun Microsystems was written in C using some libraries from C++.

Java Interpreter - We can run Java on most platforms provided a platform must has a Java interpreter. That is why Java applications are platform independent. Java interpreter translates the Java bytecode into the code that can be understood by the Operating System. Basically, A Java interpreter is a software that implements the Java virtual machine and runs Java applications. As the Java compiler compiles the source code into the Java bytecode, the same way the Java interpreter translates the Java bytecode into the code that can be understood by the Operating System.
When a Java interpreter is installed on any platform that means it is JVM (Java virtual machine) enabled platform. It (Java Interpreter) performs all of the activities of the Java run-time system. It loads Java class files and interprets the compiled byte-code. You would be glad to know that some web browsers like Netscape and the Internet Explorer are Java enabled. This means that these browsers contain Java interpreter. With the help of this Java interpreter we download the Applets from the Internet or an intranet to run within a web browser.