https://openjdk.java.net/ 
public interface jdk.incubator.http.internal.common.MinimalFuture$ExceptionalSupplier<U>
  minor version: 0
  major version: 59
  flags: flags: (0x0601) ACC_PUBLIC, ACC_INTERFACE, ACC_ABSTRACT
  this_class: jdk.incubator.http.internal.common.MinimalFuture$ExceptionalSupplier
  super_class: java.lang.Object
{
  public abstract U get();
    descriptor: ()Ljava/lang/Object;
    flags: (0x0401) ACC_PUBLIC, ACC_ABSTRACT
    Exceptions:
      throws java.lang.Throwable
    Signature: ()TU;
}
Signature: <U:Ljava/lang/Object;>Ljava/lang/Object;
SourceFile: "MinimalFuture.java"
NestHost: jdk.incubator.http.internal.common.MinimalFuture
InnerClasses:
  public abstract ExceptionalSupplier = jdk.incubator.http.internal.common.MinimalFuture$ExceptionalSupplier of jdk.incubator.http.internal.common.MinimalFuture
    RuntimeVisibleAnnotations: 
      java.lang.FunctionalInterface()