String类之intern()API说明部分：When the intern method is invoked, if the pool already contains a str
String类之intern()
API说明部分：
When the intern method is invoked, if the pool already contains a string equal to this String object as determined by the equals(Object) method, then the string from the pool is returned. Otherwise, this String object is added to the pool and a reference to this String object is returned.
测试1：
------------------------------------------------------------------