Pass type parameter to method of interface

Question

There's the following class:

public abstract class AbstractWriter<T extends BE> {

    protected final T be;
    // Constructor, some methods

    public static interface Setter {
       void setNewValue();
    }

    protected <S> void setValue(final Class<S> clazz, final S oldValue,
        final S newValue, final Setter setter) {
        // Do something
        setter.setNewValue();
        // Do something
    }       
}

Then there's PersonWriter , which extends AbstractWriter and looks currently like this:

public class PersonWriter extends AbstractWriter<BEPerson> {

    public PersonWriter(BEPerson be) {
        super(be);
    }

    public void setName(String oldValue, final String newValue) {
        setValue(String.class, oldValue, newValue, new Setter() {
            @Override
            public void setNewValue() {
                be.setName(newValue);
            }
        });
    };
}

But I want setName to look like this:

    public void setName(String oldValue, String newValue) {
        setValue(String.class, oldValue, newValue, new Setter() {
            @Override
            public void setNewValue(String newValue) {
                be.setName(newValue);
            }
        });
    };

How do I have to modify AbstractWriter , to make it work (if it's even possible)?

Answer 1

You seem to be going a rather long way to call a setter function on a field ;-). How is the new Setter() in the setValue call you want to have supposed to know when newValue is a String and when it is something else?

With a type parameter for setter, I think it should not be difficult:

public abstract class AbstractWriter<T extends BE> {
    //...
    public static interface Setter<S> {
        void setNewValue(S newValue);
    }

    protected <S> void setValue(final Class<S> clazz, final S oldValue,
        final S newValue, final Setter<S> setter) {
        // Do something
        setter.setNewValue(newValue);
        // Do something
    }    
}   

Answer 2

Is this what you are looking for?

class BE {
}

class BEPerson extends BE {
    void setName(String s) {}
    void setAge(Integer i) {}
}

public abstract class AbstractWriter<T extends BE> {

    protected final T be;
    // Constructor, some methods
    AbstractWriter(T be) { this.be = be; }

    public static interface Setter<S> {
       void setNewValue(S v);
    }

    protected <S> void setValue(final Class<S> clazz, final S oldValue,
        final S newValue, final Setter setter) {
        // Do something
        setter.setNewValue(newValue);
        // Do something
    }       
}

class PersonWriter extends AbstractWriter<BEPerson> {

    public PersonWriter(BEPerson be) {
        super(be);
    }

    public void setName(String oldValue, final String newValue) {
        setValue(String.class, oldValue, newValue, new Setter<String>() {
            @Override
            public void setNewValue(String newValue) {
                be.setName(newValue);
            }
        });
    };

    public void setAge(Integer oldValue, final Integer newValue) {
        setValue(Integer.class, oldValue, newValue, new Setter<Integer>() {
            @Override
            public void setNewValue(Integer newValue) {
                be.setAge(newValue);
            }
        });
    };
}