介绍Java 的实用工具类库java.util 包。在这个包中，Java 提供了一些实用的

方法和数据结构。例如，Java 提供日期(Data)类、日历(Calendar)类来产生和获取

日期及时间，提供随机数(Random)类产生各种类型的随机数，还提供了堆栈

(Stack)、向量(Vector) 、位集合(Bitset)以及哈希表(Hashtable)等类来表示相应的

数据结构.-Introduction of Java Utility library java.util package. In this package, Java provides some practical

Methods and data structures. For example, Java provides the date (Data) class calendar (Calendar) class to generate and access

Date and time, providing a random number (Random) class produces various types of random numbers, but also provides the stack

(Stack), vector (Vector), bit set (Bitset) and hash table (Hashtable) and other classes to represent the corresponding Data Structures.