https://openjdk.java.net/ 
public interface com.sun.management.UnixOperatingSystemMXBean extends com.sun.management.OperatingSystemMXBean
  minor version: 0
  major version: 59
  flags: flags: (0x0601) ACC_PUBLIC, ACC_INTERFACE, ACC_ABSTRACT
  this_class: com.sun.management.UnixOperatingSystemMXBean
  super_class: java.lang.Object
{
  public abstract long getOpenFileDescriptorCount();
    descriptor: ()J
    flags: (0x0401) ACC_PUBLIC, ACC_ABSTRACT

  public abstract long getMaxFileDescriptorCount();
    descriptor: ()J
    flags: (0x0401) ACC_PUBLIC, ACC_ABSTRACT
}
SourceFile: "UnixOperatingSystemMXBean.java"