Question

I have several interfaces all with the same constants – ID and ROOT. I also have a method into which I pass an object that will be an implementation of one of these interfaces.

How can I dynamically retrieve the value of the constant depending on the class passed in – i.e. I want to do something like the following:

public void indexRootNode(Node node, Class rootNodeClass)
{
    indexService.index(node, rootNodeClass.getConstant('ID'), 
        rootNodeClass.getConstant('ROOT'));
}

In PHP this is easy, but is this possible in Java? I’ve seen this problem solved using accessors on the constant, but I want to retrieve the constant directly. Annotations won’t help me here either.

Thanks

Answer 1

This can be achieved using reflection (also see corresponding javadoc).

public void indexRootNode(Node node, Class rootNodeClass)
{
    Field idField = rootNodeClass.getField("ID");
    Object idValue = idField.get(null);
    Field rootField = rootNodeClass.getField("ROOT");
    Object rootValue = rootField.get(null);

    indexService.index(node, idValue, rootValue);
}

Maybe you may additionaly have to cast the values to the corresponding type.