https://www.graalvm.org/ 
public interface org.graalvm.tools.insight.test.InsightAPI$OnEventHandler extends org.graalvm.tools.insight.test.InsightAPI$Handler
  minor version: 0
  major version: 59
  flags: flags: (0x0601) ACC_PUBLIC, ACC_INTERFACE, ACC_ABSTRACT
  this_class: org.graalvm.tools.insight.test.InsightAPI$OnEventHandler
  super_class: java.lang.Object
{
  public abstract void event(org.graalvm.tools.insight.test.InsightAPI$OnEventHandler$Context, java.util.Map<java.lang.String, java.lang.Object>);
    descriptor: (Lorg/graalvm/tools/insight/test/InsightAPI$OnEventHandler$Context;Ljava/util/Map;)V
    flags: (0x0401) ACC_PUBLIC, ACC_ABSTRACT
    Signature: (Lorg/graalvm/tools/insight/test/InsightAPI$OnEventHandler$Context;Ljava/util/Map<Ljava/lang/String;Ljava/lang/Object;>;)V
    MethodParameters:
       Name  Flags
      ctx    
      frame  
}
SourceFile: "InsightAPI.java"
NestHost: org.graalvm.tools.insight.test.InsightAPI
InnerClasses:
  public abstract Handler = org.graalvm.tools.insight.test.InsightAPI$Handler of org.graalvm.tools.insight.test.InsightAPI
  public abstract OnEventHandler = org.graalvm.tools.insight.test.InsightAPI$OnEventHandler of org.graalvm.tools.insight.test.InsightAPI
  public abstract Context = org.graalvm.tools.insight.test.InsightAPI$OnEventHandler$Context of org.graalvm.tools.insight.test.InsightAPI$OnEventHandler
    RuntimeVisibleAnnotations: 
      java.lang.FunctionalInterface()