Question

I want a method that extracts the data from a JSON-object parsed before as the correct type. The JSONObject (rawdata) extends Map, so it looks like this:

private <Type> Type getValue(String key, Type def)
{
    if (!rawdata.containsKey(key)) return def;
    if (!(rawdata.get(key) instanceof Type)) return def;
    return (Type) rawdata.get(key);
}

The instanceof obviously generates a compile-time-error. The parameter def is the default-value, returned if the key is not available or has the wrong type. But def can also be null, so def.getClass() isn’t working.

Any ideas how I can check the content of the Map-entry for the correct type?

Answer 1

Due to type erasure, the only way to handle the case where the default value can be null is to have the method require an additional parmeter of type Class – which is generally better because it allows the default value to be a subclass of the required type.