具有通用列表的Java抽象类

Question

I'm trying to define an abstract class that takes in a List of things and does stuff. Something like:

abstract public class AbstractClass {
    private final List<?> list;

    public AbstractClass(List<?> list) {
        this.list = list;
    }

    public List<?> getList() { return list; }
    abstract void addToList(List<?> list);
}

public class Class1 extends AbstractClass {
    public Class1(List<Integer> list) {
        super(list);
    }

    @Override
    void addToList(List<Integer> list) {
        // do stuff
    }
}

public class Class2 extends AbstractClass {
    public Class2(List<String> list) {
        super(list);
    }

    @Override
    void addToList(List<String> list) {
        // do stuff
    }
}


List<Integer> a = new List<Integer>();
Class1 c1 = new Class1(a);
List<Integer> b = c1.getList();
c1.addToList(a);

List<String> c = new List<String>();
Class2 c2 = new Class2(c);
List<Integer> d = c2.getList();
c2.addToList(c);

Having addToList with specific types in the subclasses is generating errors, but I don't know if that's a matter of syntax (with my poor knowledge of generics) or what I'm trying to do itself (is it possible to overload an abstract method like that)?

Answer 1

You should make AbstractClass a typed class instead of using the ? wildcard.

abstract public class AbstractClass<T> {
    private final List<T> list;

    public AbstractClass(List<T> list) {
        this.list = list;
    }

    public List<T> getList() { return list; }
    abstract void addToList(List<T> list);
}

In this case, you would have

public class Class1 extends AbstractClass<Integer> { ... }
public class Class2 extends AbstractClass<String> { ... }