在类结构中，"is a"和"has a"的不同点
2012-12-04 10:02
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is a：代表类之间的继承关系。比如PC机是计算机，工作站也是计算机。PC机和工作站是两种不同类型的计算机，但都继承了计算机的共同点特性。因此，在用Java语言实现时，应该将PC机和工作站定义成两种类，均继承计算机类。
has a：代表对象和它的成员的从属关系。同一种类的对象，通过它们的属性的不同值来区别。比如一台PC机的操作系统是Windows，另一台PC机的操作系统是Linux。操作系统是PC机的一个成员变量，根据这一成员变量的不同值可以区分不同的PC机对象。
has a：代表对象和它的成员的从属关系。同一种类的对象，通过它们的属性的不同值来区别。比如一台PC机的操作系统是Windows，另一台PC机的操作系统是Linux。操作系统是PC机的一个成员变量，根据这一成员变量的不同值可以区分不同的PC机对象。
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