question: static DiskId createDiskId ( long maxOplogSize , boolean isPersistenceType , boolean needsLinkedList ) { long bytes = maxOplogSize * 1024 * 1024 ; if ( bytes > Integer . MAX_VALUE ) { if ( isPersistenceType ) { if ( needsLinkedList ) { return new PersistenceWithLongOffset ( ) ; } else { return new PersistenceWithLongOffsetNoLL ( ) ; } } else { if ( needsLinkedList ) { return new OverflowOnlyWithLongOffset ( ) ; } else { return new OverflowOnlyWithLongOffsetNoLL ( ) ; } } } else { if ( isPersistenceType ) { if ( needsLinkedList ) { return new PersistenceWithIntOffset ( ) ; } else { return new PersistenceWithIntOffsetNoLL ( ) ; } } else { if ( needsLinkedList ) { return new OverflowOnlyWithIntOffset ( ) ; } else { return new OverflowOnlyWithIntOffsetNoLL ( ) ; } } } }
target:  Creates appropriate instance of DiskId depending upon the maxOplogSize set by the user. If the maxOplogSize (in bytes) is greater than Integer.MAX_VALUE, LongOplogOffsetDiskId will be created and for maxOplogSize lesser than that, IntOplogOffsetDiskId will be created.