Unnamed Classes and Instance main Methods (Preview)

This document describes changes to the Java Virtual Machine Specification to support Unnamed Classes and Instance main Methods, which is a preview feature of Java SE 21. See JEP 445 for an overview of the feature.

A companion document describes the changes needed to the Java Language Specification to support Unnamed Classes and Instance main Methods.

Changes are described with respect to existing sections of the JLS. New text is indicated like this and deleted text is indicated like this. Explanation and discussion, as needed, is set aside in grey boxes.

Chapter 5: Loading, Linking, and Initializing

5.2 Java Virtual Machine Startup

The Java Virtual Machine starts up by creating an initial class or interface using the bootstrap class loader (5.3.1) or a user-defined class loader (5.3.2). The Java Virtual Machine then links the initial class or interface, initializes it, and invokes the public static method void main(String[]) a main method, as described in (JLS 12.1.4). The invocation of this method drives all further execution. Execution of the Java Virtual Machine instructions constituting the main method may cause linking (and consequently creation) of additional classes and interfaces, as well as invocation of additional methods.

The initial class or interface is specified in an implementation-dependent manner. For example, the initial class or interface could be provided as a command line argument. Alternatively, the implementation of the Java Virtual Machine could itself provide an initial class that sets up a class loader which in turn loads an application. Other choices of the initial class or interface are possible so long as they are consistent with the specification given in the previous paragraph.