Java: Unboxing values stored in an Object to an unknown type

Question

I am building something like a data flow graph, with nodes and connections that pass data between them. The base class in this case is ValueTarget<T>, which has a previous and a next target to pass data back and forth. Other classes extend this class to provide sources for the data, merge data (e.g. a multiplication) etc.

Now, I wanted to write a data source that takes its value from any given method. It takes a java.lang.reflect.Method instance (and the Object and parameters to invoke it) and uses this to set the data:

@Override
public T getValue() {

    if (valueCalculator != null) {
        try {
            Object result = valueCalculator.invoke(sourceObject);
            T typedResult = (T)(result);
            return typedResult;
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

    return super.getValue();
}

Now, I have tried this with the public int getLength() Method of another object. However, in the graph, I need to map this method to a float result. The given typecast doesn't throw an Exception, but when reading the last ValueTarget<Float>'s value and using its result as a float parameter to another method, the program crashes, stating that "java.lang.Integer cannot be cast to java.lang.Float".

Now, I am aware that Integer and Float are boxed and therefore cannot be cast into each other's type. However, as the types are all handled using the generics, I cannot unbox to a specific type.

Is there any way to perform a generic unboxing in order to be able to cast boxed values into the according value-types?

Answer 1

How about using Number.floatValue()?

Object result = valueCalculator.invoke(sourceObject);
Float f = ((Number)result).floatValue();
System.out.println(f);

... or however you want to use it.

Here I'm assuming the return type is one of these - BigDecimal, BigInteger, Byte, Double, Float, Integer, Long, and Short (which are all subclasses of Number).

Answer 2

You can use Apache CommonBeanUtils library to convert types at runtime.

org.apache.commons.beanutils.ConvertUtils.convert(Object value, Class targetType)

so you change the typecaste code

  T typedResult = (T)(result);

replace with this

 T typedResult = (T)org.apache.commons.beanutils.ConvertUtils.convert(result, T.getClass());