Enumeration was around in the very early days of
Java. It was basically a "first pass" at iteration. Collections were somewhat less organized in those days.
When Java 1.2 came out around 1998, they included a new Collections Framework. ArrayList is the preferred replacement for Vector, HashMap for Hashtable, and Iterator replaces Enumeration. The new classes have similar functionality to the ones they replace, but they were designed more cohesively to work together and be consistent as part of the framework, and to improve on the originals in various ways. However, by this time there was a lot of code already out there using Vector, Hashtable, and Enumeration, so they couldn't just get rid of them.
Dont' use Vector, Hashtable, or Enumeration unless you have to, due to interacting with legacy code.