class It can inherit to other class only one class. The abstract class needs to use 'override'. interface It can inherit to multiple class. It does not need to use 'override'. Ex) 1. Create the abstract class(parents). (uncompleted method) 2. Create the interface. Using with 'I' in accordance with the custom. (uncompleted method) 3. Create the class(children) which is inherited 1,2. # 1 abstract..