Clean-room Java implementations include Kaffe and IBM J9.Oracle owns the Java trademark and may allow its use to certify implementation suites as fully compatible with Oracle's specification.

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Every Java virtual machine implementation must have a bootstrap class loader, capable of loading trusted classes.

The Java virtual machine specification doesn't specify how a class loader should locate classes. The JVM has a garbage-collected heap for storing objects and arrays.

More complex than just emulating bytecode is compatibly and efficiently implementing the Java core API that must be mapped to each host operating system.

These instructions operate on a set of common A JVM language is any language with functionality that can be expressed in terms of a valid class file which can be hosted by the Java Virtual Machine.

Thus, the JVM is both a stack machine and a register machine.

A 64-bit version of Java is available, The aim is binary compatibility.Having a specification ensures interoperability of Java programs across different implementations so that program authors using the Java Development Kit (JDK) need not worry about idiosyncrasies of the underlying hardware platform.The JVM reference implementation is developed by the Open JDK project as open source code and includes a JIT compiler called Hot Spot.Oracle provides tests that verify the proper operation of implementations of the Java Virtual Machine.One of Oracle's JVMs is named Hot Spot, the other, inherited from BEA Systems is JRockit.The JVM operates on primitive values (integers and floating-point numbers) and references. Code, constants, and other class data are stored in the "method area".