Question

关于Enumeration和Iterator的区别．

有如下代码：
java.util.Enumeration params = this.getServletConfig().getInitParameterNames();
如果这样写就是正确的．但是如果我换成．
java.util.Iterator params = this.getServletConfig().getInitParameterNames();
eclipse就会报错，说是enumeration不能转换成iterator类型．
请问是为什么？明明enumeration比iterator还要老嘛．为什么他确能用而iterator不能用．

Answer 1

this.getServletConfig().getInitParameterNames();
这个方法的返回值必须是枚举类型的，具体这两个的差别好像是访问集合类的时候，Iterator能用remove（）的方法进行删除，而Enumeration则不能进行删除~
你想如果用Iterator你把初始化参数删除了，那也不符合常理吧~

Answer 2

An iterator over a collection. Iterator takes the place of Enumeration in the Java collections framework. Iterators differ from enumerations in two ways:
1.Iterators allow the caller to remove elements from the underlying collection during the iteration with well-defined semantics.
void remove() ：Removes from the underlying collection the last element returned by the iterator (optional operation).This method can be called only once per call to next. The behavior of an iterator is unspecified if the underlying collection is modified while the iteration is in progress in any way other than by calling this method。
2.Method names have been improved

/×××××××××××××××××××××××××××××/
java.util
Interface Iterator<E>

All Known Subinterfaces:
ListIterator<E>, XMLEventReader
-------------------------------------------------
java.util
Interface Enumeration<E>

All Known Subinterfaces:
NamingEnumeration<T>
/×××××××××××××××××××××××××××××/
An object that implements the Enumeration interface generates a series of elements, one at a time. Successive calls to the nextElement method return successive elements of the series.