Difference between a Java interpreter and JVM

Question

I have heard people saying "a JVM is necessarily a Java interpreter but a Java interpreter is not necessarily a JVM". Is that true?

I mean is there a difference between a Java interpreter and JVM?

Answer 1

Yes, there is a difference.

Java virtual machine:

A software "execution engine" that safely and compatibly executes the byte codes in Java class files on a microprocessor (whether in a computer or in another electronic device).

Java interpreter:

A module that alternately decodes and executes every statement in some body of code. The Java interpreter decodes and executes bytecode for the Java virtual machine.

The Java interpreter is actually a part of JVM. Virtual machine is not just executing the bytecodes, it has lot of tasks to do. That full-fledged environment is referred to as a JVM.

Check:

• Java Virtual Machine

• Java SE HotSpot at a Glance

Answer 2

Simply put, a JVM interprets bytecode and a Java interpreter interprets Java. They are different because bytecode and Java are different languages.

Bytecode is a low-level language, like machine code. The bytecode is meant to be run by a program called a bytecode interpreter, also called a virtual machine. The purpose of bytecode is to be easy to interpret.

Java is a higher-level language, like C or Python. These languages can be interpreted too: you just write a program that can run their code. It doesn't have to involve bytecode. It's just that higher-level languages are harder to interpret directly.

Java is usually "interpreted" by translating the Java program into a bytecode program first. Then the Java Virtual Machine (JVM) runs the bytecode.

But you could interpret any language this way. The JVM could interpret other languages if you translated them into the right bytecode.

You can also interpret a programming language directly, without any bytecode. Some BASIC interpreters just look for BASIC instructions in the sourcecode and execute them. They don't make make a new program in a different language first. If you did the same thing for Java, it would be a Java interpreter but not a JVM.