https://openjdk.java.net/ 
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package com.sun.source.util;

import java.util.ServiceLoader;
import javax.tools.StandardLocation;


The interface for a javac plug-in.

The javac plug-in mechanism allows a user to specify one or more plug-ins
on the javac command line, to be started soon after the compilation
has begun. Plug-ins are identified by a user-friendly name. Each plug-in that
is started will be passed an array of strings, which may be used to
provide the plug-in with values for any desired options or other arguments.

Plug-ins are located via a ServiceLoader, using the same class path as annotation processors (i.e. ANNOTATION_PROCESSOR_PATH or -processorpath). 
It is expected that a typical plug-in will simply register a TaskListener to be informed of events during the execution of the compilation, and that the rest of the work will be done by the task listener. 
Since:1.8
/**
 * The interface for a javac plug-in.
 *
 * <p>The javac plug-in mechanism allows a user to specify one or more plug-ins
 * on the javac command line, to be started soon after the compilation
 * has begun. Plug-ins are identified by a user-friendly name. Each plug-in that
 * is started will be passed an array of strings, which may be used to
 * provide the plug-in with values for any desired options or other arguments.
 *
 * <p>Plug-ins are located via a {@link ServiceLoader},
 * using the same class path as annotation processors (i.e.
 * {@link StandardLocation#ANNOTATION_PROCESSOR_PATH ANNOTATION_PROCESSOR_PATH} or
 * {@code -processorpath}).
 *
 * <p>It is expected that a typical plug-in will simply register a
 * {@link TaskListener} to be informed of events during the execution
 * of the compilation, and that the rest of the work will be done
 * by the task listener.
 *
 * @since 1.8
 */
public interface Plugin {
    
Returns the user-friendly name of this plug-in.

Returns:the user-friendly name of the plug-in
/**
     * Returns the user-friendly name of this plug-in.
     * @return the user-friendly name of the plug-in
     */
    String getName();

    
Initializes the plug-in for a given compilation task.

Params:
  • task – The compilation task that has just been started
  • args – Arguments, if any, for the plug-in
/**
     * Initializes the plug-in for a given compilation task.
     * @param task The compilation task that has just been started
     * @param args Arguments, if any, for the plug-in
     */
    void init(JavacTask task, String... args);

    
Returns whether or not this plugin should be automatically started,
even if not explicitly specified in the command-line options.

This method will be called by javac for all plugins located by the service loader. If the method returns true, the plugin will be initialized with an empty array of string arguments if it is not otherwise initialized due to an explicit command-line option. 
Returns:whether or not this plugin should be automatically started
/**
     * Returns whether or not this plugin should be automatically started,
     * even if not explicitly specified in the command-line options.
     *
     * <p>This method will be called by javac for all plugins located by the
     * service loader. If the method returns {@code true}, the plugin will be
     * {@link #init(JavacTask,String[]) initialized} with an empty array of
     * string arguments if it is not otherwise initialized due to an explicit
     * command-line option.
     *
     * @return whether or not this plugin should be automatically started
     */
    default boolean autoStart() {
        return false;
    }
}