The normal reason for getting this error is, since the abstract class doesn't have a default constructor all the constructors of the extending class must have "super(title);" as the first staement in their constructors. The code snip you showed us should be fine.
Hi Hiep, You have a syntax error on your first ListForm class declaration: it should be abstract class instead of class abstract but that should not cause the error you say the compiler is indicating. By changing that, your code should compile. There must be some problem in the implementation of the abstract methods. Hope this helps, Michael Morris
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