What is Java Virtual Machine?

The Java Virtual Machine (JVM) is a real name dropper when you’re programming in Java. When your Java project builds, it translates the source code (contained in *.java source files) to Java bytecode (most often contained in *.class files). This takes your high-level code one step closer to machine code, but not quite there yet. This bytecode is a collection of compact instructions; easier for a machine to interpret, but less readable.

When you run a Java application on your computer, cellphone, or any other Java-enabled platform, you essentially pass this Java bytecode to the Java Virtual Machine. The interpreter in the Java Virtual Machine usually starts compiling the entire bytecode at runtime, following the principles of so-called just-in-time compilation. This makes for the typical, albeit often slight delay when opening a Java application, but generally enhances the program performance compared to interpreted compilation. The main advantage of this system is the increased compatibility. Since your applications run in a virtual machine instead of directly on your hardware, the developer can program and build their application once, which can then be executed on every device with an implementation of the Java Virtual Machine. This principle has given birth to the Java slogan: “Write once, run everywhere.”