Java (and Clojure) code is not executed directly. Instead, it is compiled into an architecture-independent binary format which is executed by a Java Virtual Machine (JVM). The behaviour of the JVM is defined by the Java Virtual Machine Specification. Multiple implementations of this standard are available.

Java source files are converted to their binary representation (called .class files) by a compiler, javac. javac, along with various other tools used for Java development are included in the Java Development Kit (JDK). Each release of the Java platform has a corresponding JDK for development.

Java Virtual Machine

The JVM is a virtual machine which defines its own instruction set, referred to a Java bytecode. The process of locating, loading, verifying and executing this bytecode is define by the JVM specification. After installing a Java distribution, the JVM can be invoked via the java command.

Java Development Kit

Like the JVM, the Java language is also defined by a language specification. Compilers are responsible for compiling Java source files to class files according to this specification. The javac compiler, along with various other tools useful for development such as javap and jstack are distributed as part of the Java Development Kit (JDK).