具有接口和抽象类的Java通用设置器

Question

i have a problem with an Interface and generic setters that i tried to solve for some hours now.

i have an interface where i want to define some getter and setter functions. the getter functions should be implemented by some abstract class since they usually shouldn't change. the setter functions on the other hand should be overrideable multiple times by a defined class. In the case i try to describe it would be that the childClass should be able to implement 2 setFunctions with the same name and different input values

 Interface TestClass {     
      public abstract void setSomething(List<?> value);
      public abstract List<String> getSomething();
 }

 abstract class AbstractTestClass  implements TestClass {

      List<String> someData;

      public List<String> getSomething() {
          return someData;
      }
 }

 class TestClassImplementation extends AbstractTestClass() {

      @Override
      public void setSomething(List<String> data) {
         someData = data;
      }

      @Override
      public void setSomething(List<SomeOtherType> data) {
         someData = convertToStringList(data);
      }

      private List<String> convertToStringList(List<SomeOtherType> data) {
         ... do some conversion ...
         return returnList;
      }
 }

hope this gives the idea of what i want to do. I would even prefer to implement the setSomething with the stringlist in the abstract class. But both setters must be reachable. Thanks

Answer 1

You simply can't do that. Generics are not retained at runtime (google type erasure for more infos on this or just read the wikipedia page).

This means that your setSomething-methods all have the same signature, as their only parameter is of type List .

Answer 2

Well, you should try with generic solution:

Interface TestClass<T> { //Generic type T that you will provide when extending with actual class

    public abstract void setSomething(List<T> value);
    public abstract List<T> getSomething();
}

class TestClassImplementation extends AbstractTestClass<RealType> {

    @Override
    public void setSomething(List<RealType> data) {
       someData = data;
    }
}

The thing that confuses you is that the wildcard sign ? does not mean it changes any type, it just denotes an unknown type.