Question

I am currently trying to achieve something like this:
Based on this class, I try to create a new instance of the class Class<? extends AbstractValidator> returned by the method getValidator().

public abstract class AbstractEnumDefinition
       extends AbstractRequestFieldDefinition {

    private Vector<String> values = new Vector<String>();

    public abstract void define(String lang);

    protected void addEnumDefinition(String value){
        values.add(value);
    }

    public Vector<String> getValues(){
        return values;
    }

    @Override
    public Class<? extends AbstractValidator> getValidator() {
        return new AbstractValidator() {
            @Override
            public boolean isValid(String value) {
                return values.contains(value);
            }

            @Override
            public String getDefaultValue() {
                return "";
            }
        }.getClass();
    }
}

Say I create this class:

public class LanguageDefinition extends AbstractEnumDefinition {

    public LanguageDefinition() {
        super();
    }

    @Override
    public void define(String language) {
        addEnumDefinition("BEL-fr");
        addEnumDefinition("BEL-nl");
        addEnumDefinition("BEL-en");
    }
}

Later in my code, I call

new LanguageDefinition().getValidator().getConstructor().newInstance()

The class I am trying to instantiate here is not declared anywhere, but “generated dynamically”/”dynamically created” within the AbstractEnumDefinition class.

When trying to do this, I get an java.lang.InstantiationException for

be....servlets.model.extraction.filter.editor.AbstractEnumDefinition$1

I guess this is due to the fact that this Class has to be explicitly created before hand, and not referenced dynamically?

Is there some kind of solution that would allow me to not have to write one class per validator?

Thanks for the help,

Eric

Answer 1

I can only make assumptions since i don’t see the code where you are actually using the class, but you should check: http://docs.oracle.com/javase/6/docs/api/java/lang/InstantiationException.html

One thing it mentions is the instantiation can fail is the class is an abstract class (perfectly logical since you can’t instantiate abstract classes).

Also, i don’t see why you need to return the class and then create and object. Why not just define a Validator Interface and have your method return a Validator object.