由于大型应用程序中组件的通信方式，所以假设对象实例的创建者就是它的用户并不总是安全的。
Because of the way components in large applications communicate, it's not always safe to assume that the creator of an object instance is its user.
只有当对象创建后，实例的初始化才开始执行。
Instance initializers are executed only if an object is constructed.
Creator类用于定义创建产品对象实例的Factory方法。
Creator classes are used to define factory methods that create instances of the product objects.
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