为什么通用类可以实现具有不同类型参数的接口？

Question

For example like in this section

interface MyGenericsI<A, B, C>{
    public A getA();
    public B getB();
    public C getC();
}

abstract class MyGenerics<D> implements MyGenericsI{
}

Answer 1

Because the fields or methods that make use of the class' generic type(s) might be unrelated to the methods of the interface. Contrived example:

public class Company<P> implements List<Employee> {
    public P produceProduct();
    public Employee get(int index) { ... }
    ...
}

Here, a Company<P> is capable of producing products of the generic type P , so that you could eg create a Company<Computer> that makes computers. However, a company also has employees, so you could make it implement the methods of List<Employee> in order to access the employees of the company (composition would be better in this example, though).