https://openjdk.java.net/ 
public interface java.util.function.DoubleSupplier
  minor version: 0
  major version: 59
  flags: flags: (0x0601) ACC_PUBLIC, ACC_INTERFACE, ACC_ABSTRACT
  this_class: java.util.function.DoubleSupplier
  super_class: java.lang.Object
{
  public abstract double getAsDouble();
    descriptor: ()D
    flags: (0x0401) ACC_PUBLIC, ACC_ABSTRACT
}
SourceFile: "DoubleSupplier.java"
    RuntimeVisibleAnnotations: 
      java.lang.FunctionalInterface()