On linux (Ubuntu 18.04) doing this:

$ jextract -d classes /usr/include/time.h

results in the following classes being generated:

$ ls classes/

 features.class
 META-INFO
 stdc_predef.class
 time.class
'time$pid_t.class'
'time$sigevent.class'
 x86_64_linux_gnu_bits_time.class
'x86_64_linux_gnu_bits_types$__blkcnt64_t.class'
'x86_64_linux_gnu_bits_types$__blkcnt_t.class'
'x86_64_linux_gnu_bits_types$__blksize_t.class'
'x86_64_linux_gnu_bits_types$__caddr_t.class'
 x86_64_linux_gnu_bits_types.class
 x86_64_linux_gnu_bits_types_clockid_t.class
'x86_64_linux_gnu_bits_types$__clockid_t.class'
'x86_64_linux_gnu_bits_types_clockid_t$clockid_t.class'
 x86_64_linux_gnu_bits_types_clock_t.class
'x86_64_linux_gnu_bits_types$__clock_t.class'
'x86_64_linux_gnu_bits_types_clock_t$clock_t.class'
'x86_64_linux_gnu_bits_types$__daddr_t.class'
'x86_64_linux_gnu_bits_types$__dev_t.class'
'x86_64_linux_gnu_bits_types$__fsblkcnt64_t.class'
'x86_64_linux_gnu_bits_types$__fsblkcnt_t.class'
'x86_64_linux_gnu_bits_types$__fsfilcnt64_t.class'
'x86_64_linux_gnu_bits_types$__fsfilcnt_t.class'
'x86_64_linux_gnu_bits_types$__fsid_t.class'
'x86_64_linux_gnu_bits_types$__fsword_t.class'
'x86_64_linux_gnu_bits_types$__gid_t.class'
'x86_64_linux_gnu_bits_types$__id_t.class'
'x86_64_linux_gnu_bits_types$__ino64_t.class'
'x86_64_linux_gnu_bits_types$__ino_t.class'
'x86_64_linux_gnu_bits_types$__int16_t.class'
'x86_64_linux_gnu_bits_types$__int32_t.class'
'x86_64_linux_gnu_bits_types$__int64_t.class'
'x86_64_linux_gnu_bits_types$__int8_t.class'
'x86_64_linux_gnu_bits_types$__intmax_t.class'
'x86_64_linux_gnu_bits_types$__intptr_t.class'
 x86_64_linux_gnu_bits_typesizes.class
'x86_64_linux_gnu_bits_types$__key_t.class'
 x86_64_linux_gnu_bits_types___locale_t.class
 x86_64_linux_gnu_bits_types_locale_t.class
'x86_64_linux_gnu_bits_types___locale_t$__locale_data.class'
'x86_64_linux_gnu_bits_types___locale_t$__locale_struct.class'
'x86_64_linux_gnu_bits_types___locale_t$__locale_t.class'
'x86_64_linux_gnu_bits_types_locale_t$locale_t.class'
'x86_64_linux_gnu_bits_types$__loff_t.class'
'x86_64_linux_gnu_bits_types$__mode_t.class'
'x86_64_linux_gnu_bits_types$__nlink_t.class'
'x86_64_linux_gnu_bits_types$__off64_t.class'
'x86_64_linux_gnu_bits_types$__off_t.class'
'x86_64_linux_gnu_bits_types$__pid_t.class'
'x86_64_linux_gnu_bits_types$__quad_t.class'
'x86_64_linux_gnu_bits_types$__rlim64_t.class'
'x86_64_linux_gnu_bits_types$__rlim_t.class'
'x86_64_linux_gnu_bits_types$__sig_atomic_t.class'
'x86_64_linux_gnu_bits_types$__socklen_t.class'
'x86_64_linux_gnu_bits_types$__ssize_t.class'
 x86_64_linux_gnu_bits_types_struct_itimerspec.class
'x86_64_linux_gnu_bits_types_struct_itimerspec$itimerspec.class'
 x86_64_linux_gnu_bits_types_struct_timespec.class
'x86_64_linux_gnu_bits_types_struct_timespec$timespec.class'
 x86_64_linux_gnu_bits_types_struct_tm.class
'x86_64_linux_gnu_bits_types_struct_tm$tm.class'
'x86_64_linux_gnu_bits_types$__suseconds_t.class'
'x86_64_linux_gnu_bits_types$__syscall_slong_t.class'
'x86_64_linux_gnu_bits_types$__syscall_ulong_t.class'
 x86_64_linux_gnu_bits_types_timer_t.class
'x86_64_linux_gnu_bits_types$__timer_t.class'
'x86_64_linux_gnu_bits_types_timer_t$timer_t.class'
 x86_64_linux_gnu_bits_types_time_t.class
'x86_64_linux_gnu_bits_types$__time_t.class'
'x86_64_linux_gnu_bits_types_time_t$time_t.class'
'x86_64_linux_gnu_bits_types$__u_char.class'
'x86_64_linux_gnu_bits_types$__uid_t.class'
'x86_64_linux_gnu_bits_types$__uint16_t.class'
'x86_64_linux_gnu_bits_types$__uint32_t.class'
'x86_64_linux_gnu_bits_types$__uint64_t.class'
'x86_64_linux_gnu_bits_types$__uint8_t.class'
'x86_64_linux_gnu_bits_types$__u_int.class'
'x86_64_linux_gnu_bits_types$__uintmax_t.class'
'x86_64_linux_gnu_bits_types$__u_long.class'
'x86_64_linux_gnu_bits_types$__u_quad_t.class'
'x86_64_linux_gnu_bits_types$__useconds_t.class'
'x86_64_linux_gnu_bits_types$__u_short.class'
 x86_64_linux_gnu_bits_wordsize.class
 x86_64_linux_gnu_gnu_stubs_64.class
 x86_64_linux_gnu_sys_cdefs.class