JVM life cycle

JVM knows nothing about the specifics of the Java programming language. Instead, it is intimately familiar with a particular binary format—the class file format. These class files encapsulate JVM instructions, also known as bytecodes, along with a symbol table and supplementary information. To ensure security, the JVM enforces robust syntactic and structural constraints on the code contained within class files.

JVM life cycle

Instance birth

When a Java application is launched, a runtime instance of the JVM is created. This instance is responsible for executing the application’s bytecode and managing its runtime environment.

Execution

The JVM instance starts running the Java application by invoking the main() method of a designated initial class. This main() method serves as the entry point for the application and must meet specific criteria: it should be public, static, return void, and accept a single parameter, which is an array of strings, (String[]). It’s important to note that the criteria for the main() method may evolve, as a preview version in Java 21 suggests potential simplifications. Any class with such a main() method can serve as the starting point for a Java application.

Application execution

The JVM executes the Java application, processing its instructions and managing memory, threads, and other resources as needed.

Application completion

Once the Java application is executed, the JVM instance is no longer needed. At this point, the JVM instance dies.

JVM follows a one application per instance model. Suppose you start multiple Java applications concurrently on the same computer, using the same concrete implementation of the JVM. In that case, you’ll have multiple JVM instances, each dedicated to running its respective Java application. These JVM instances are isolated from each other, ensuring the independence and security of each Java application.