Java Generics构造函数的意外行为 <X,Y> （C <Y> ）和接口C. <Y>

Question

I have the following code:

A class that models the mapping between a ValueContainer<P> and an Entity E . (Eg. a checkbox (ValueContainer) and something that has a Boolean value):

public abstract class ObjValContainerMapper<E, P> {

    private ValueContainer<P> provider;

    public ObjValContainerMapper(ValueContainer<P> provider) {
        this.provider = provider;
    }

    public abstract P getValue(E entity);

    public abstract void setValue(E entity, P value);

    ...

}

An interface ValueContainer<P> :

public interface ValueContainer<T> {
        T getValue();
        void setValue(T value);
}

A custom Checkbox:

public class AdvancedCheckBox extends JCheckBox implements ValueContainer<Boolean>

And some code that unexpectedly doesn't work:

AdvancedCheckBox chckbxBindToDrive = new AdvancedCheckBox(
            "Bind to Drive");

ObjValContainerMapper<IndexSpec, Boolean> bindToDriveMapper = 
        new ObjValContainerMapper<IndexSpec, Boolean>(chckbxBindToDrive) {
    @Override
    public Boolean getValue(IndexSpec entity) {
        if (entity == null) {
            return false;
        }
        return entity.isBindToDrive();
    }
    @Override
    public void setValue(IndexSpec entity, Boolean value) {
        entity.setBindToDrive(value);
    }
};

The code does not compile. The error shown is " The constructor ObjValContainerMapper(AdvancedCheckBox) is undefined ". Eclipse suggests, among other options, to let AdvancedCheckBox implement ValueContainer or cast the argument chckbxBindToDrive to ValueContainer, despite AdvancedCheckBox explicitly declares implements ValueContainer<Boolean> . Strangely enough I have reused code from an old project that was built with Java 6, in which case the approx. same code worked fine. Has something changed with Java 7 or am I missing something?

Environment:

• Eclipse Kepler
• JDK 1.7.0_51
• some code generated with WindowBuilder (the AdvacedCheckBox declaration)

Answer 1

Thx for all the troubleshooting proposals in the comments.

The cause for this behaviour was that I copied the ValueContainer interface twice into two differnt packages as I assumed it would be missing given that Eclipse didn't seem to find it first (thx @sasankad for the proposal to clean the project). I hope this is still helpful for others as the error message and solution-proposals by the compiler and Eclipse respectively are not and are rather misleading.