Draw a dependency relationship between two classes,or between a class and an interface,to show that the client class depends on the supplier class/interface to provide certain services,such as:
The client class accesses a value (constant or variable) defined in the supplier class/interface.（访问一个属性值）
Operations of the client class invoke operations of the supplier class/interface.（访问一个方法）
Operations of the client class have signatures whose return class or arguments are instances of the supplier class/interface.（返回值或者参数是一个被依赖者实例）
A dependency relationship is a dotted line with an arrowhead at one end:The arrowhead points to the supplier class.（是一条带箭头的虚线）
2，Association Relationship
An association provides a pathway for communication. The communication can be between use cases and actors,between two classes or between a class and an interface.
Associations are the most general of all relationships and consequentially the most semantically weak. If two objects are usually considered independently,the relationship is an association
