Java:重写泛型方法
我试图重写从父类继承抽象方法的子类中的方法。我正在尝试更改通用返回类型,但我有点困惑 基本泛型类:Java:重写泛型方法,java,generics,inheritance,Java,Generics,Inheritance,我试图重写从父类继承抽象方法的子类中的方法。我正在尝试更改通用返回类型,但我有点困惑 基本泛型类: public abstract class BaseAdapter<T extends IEvent> { private List<T> events; public BaseAdapter(List<T> events) { this.events = events; } public List<T> so
public abstract class BaseAdapter<T extends IEvent> {
private List<T> events;
public BaseAdapter(List<T> events) {
this.events = events;
}
public List<T> sort() {
// Some sorting...
return newFilteredEvents;
}
}
以及从IEvent
public class Event implements IEvent {
private long id;
private long startTime, endTime;
@Override
public void setId(long id) {
this.id = id;
}
@Override
public long getId() {
return this.id;
}
// The other inherited methods...
}
我试图实现的是编写更多的抽象代码,因为这些类、接口将被多个类(在我的例子中是不同的视图类型)扩展。这些是抽象类:
BaseAdapter
,BaseView
,IEvent
,这些是实现:AdapterEvent
,EventView
,Event
,这是因为Java中泛型的类型变量没有协方差
这意味着,如果类型参数是多态的,则泛型类型没有多态性。实际上,列表
不是列表
的子类型,即使事件
事件
这就是Java提供以下功能的原因:
protected abstract BaseAdapter将BaseAdapter
更改为BaseAdapter
public abstract class BaseView extends View {
private BaseAdapter<IEvent> events;
@Override
protected View onCreate(Context context) {
View view = super.onCreate(context);
this.events = getAdapter();
return view;
}
/**
* The child class should provide an adapter
*/
protected abstract BaseAdapter<IEvent> getAdapter();
}
public class EventView extends BaseView {
@Override
protected View onCreate(Context context) {
return super.onCreate(context):
}
@Override
protected BaseAdapter<IEvent> getAdapter() {
List<Event> events = EventManager.getInstance().getEvents();
return new AdapterEvent(events);
}
}
Type mismatch: cannot convert from AdapterEvents to BaseAdapter<IEvent>
public interface IEvent {
public void setId(long id);
public long getId();
public void setStartMillis(long start);
public long getStartMillis();
public void setEndMillis(long end);
public long getEndMillis();
}
public class Event implements IEvent {
private long id;
private long startTime, endTime;
@Override
public void setId(long id) {
this.id = id;
}
@Override
public long getId() {
return this.id;
}
// The other inherited methods...
}
protected abstract BaseAdapter<? extends IEvent> getAdapter();
protected BaseAdapter<? extends IEvent> getAdapter() {
..
return new AdapterEvent(events);
}