Reference的另一个子类——软引用——可满足一个不同却相关的目的。
Another subclass of reference, soft references, fulfills a different but related purpose.
接下来，引用生成的程序，并提供子类(带有可理解的方法名)。
Next, refer to the generated program, and provide sub-classes (with understandable method names) as necessary.
注意“外部引用”不仅仅包括引用的对象，还包括可以使用的类，甚至子类。
Notice that "external references" includes not just objects that are referred to, but external classes that can be used and even subclassed.
列表值的引用存储在子类内。
尽管单例实现使用的是子类的类名，其他的模式（比如稍后介绍的活动记录模式）需要引用其他的静态属性。
Whereas the singleton implementation uses the subclass's class name, other patterns (such as active record, covered later) need to reference other static properties.
在quicktemplate子类的内部，通过覆盖这些方法，可以随心所欲地格式化和样式化类别列表和交叉引用等。
Inside the QuickTemplate subclass, you'll override methods to format and style things like category listings and cross-references the way you want.
使用类型引用和匿名类型的结构子类型转化(动态类型)。
Structural Subtyping (duck typing) using type inference and anonymous types.
AspectJ和AspectWerkz提供了一种简洁的引用多个类型的技术(例如Account +表示帐户的所有子类型)。
AspectJ and AspectWerkz offer a concise way of referring to multiple types (for example, account + indicates all subtypes of an account).
所有引用父类的地方必须能透明的使用其子类的对象。
Function that us pointers or references to base classes must be able to use obejects of derived classes without knowing it.
所有引用父类的地方必须能透明的使用其子类的对象。
Function that us pointers or references to base classes must be able to use obejects of derived classes without knowing it.
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