In general there's nothing wrong with abstract classes.
一般有抽象类没有错。
Abstract classes are those with at least one method without code.
抽象类是那些至少有一个方法没有代码。
As with abstract classes, you can define any number of method signatures.
对于抽象类，可以定义任意数目的方法签名。
You might wonder what the use is of abstract classes in such a case.
你可能想知道什么是使用抽象类在这种情况下。
If all Action classes must implement this method, make it abstract.
如果所有action类都必须实现此方法，则让其为抽象。
The product and create classes are abstract.
product和creator类是抽象的。
The product and create classes are abstract.
product和creator类是抽象的。
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