A buffer is a list of elements of a specific primitive type.

A buffer can be described by the following properties:

• Capacity: the number of elements a buffer can hold. Capacity may not be negative and never changes.
• Position: a cursor of this buffer. Elements are read or written at the position if you do not specify an index explicitly. Position may not be negative and not greater than the limit.
• Limit: controls the scope of accessible elements. You can only read or write elements from index zero to limit - 1. Accessing elements out of the scope will cause an exception. Limit may not be negative and not greater than capacity.
• Mark: used to remember the current position, so that you can reset the position later. Mark may not be negative and no greater than position.
• A buffer can be read-only or read-write. Trying to modify the elements of a read-only buffer will cause a ReadOnlyBufferException, while changing the position, limit and mark of a read-only buffer is OK.
• A buffer can be direct or indirect. A direct buffer will try its best to take advantage of native memory APIs and it may not stay in the Java heap, thus it is not affected by garbage collection.

Buffers are not thread-safe. If concurrent access to a buffer instance is required, then the callers are responsible to take care of the synchronization issues.

[Android Documentation]