void () { if (!isUsable() && !isAboutToUnmap()) { throw new IllegalStateException("Page state must be in { USABLE | ABOUT_TO_UNMAP } for accessing, but: " + this); } if (usageCount() == 0) { throw new IllegalStateException("Page must be acquired for use (i.e. usageCount>0) before accessing, but: " + this); } }