为什么java执行中线程状态标记为RUNNABLE而不是RUNNING？

A thread state. A thread can be in one of the following states:

NEW
A thread that has not yet started is in this state.
RUNNABLE
A thread executing in the Java virtual machine is in this state.
BLOCKED
A thread that is blocked waiting for a monitor lock is in this state.
WAITING
A thread that is waiting indefinitely for another thread to perform a particular action is in this state.
TIMED_WAITING
A thread that is waiting for another thread to perform an action for up to a specified waiting time is in this state.
TERMINATED
A thread that has exited is in this state.

参考：http://docs.oracle.com/javase/6/docs/api/java/lang/Thread.State.html


对于RUNNABLE状态有点违反我的常识，既然是“A thread executing”，为什么不标记为RUNNING或者EXECUTEING？
那又为什么WAITING状态不是WAITABLE？


各位认为是出于什么考虑这样做的？