TxnDoubleCallable (Multiverse Core 0.7.0)

```
public interface TxnDoubleCallable
```
A transactional callable contains the logic that needs to be executed transactionally and normally is executed by the TxnExecutor. This transactional callable is optimized for retuning a primitive type: double. Using this TxnDoubleCallable instead of the TxnCallable is that no object wrapper needs to be created and there is no reason to deal with a potential null value.

- Method Summary
  
  All Methods Instance Methods Abstract Methods
  Modifier and Type Method Description
  
  double call(Txn txn)
  Executes the callable.

- Method Detail
  - call
```
double call(Txn txn)
     throws Exception
```
    Executes the callable.
    
    Parameters:
    
    txn - the Transaction. Depending on the txn PropagationLevel, this could be null.
    
    Returns:
    
    the result of the execution.
    
    Throws:
    
    Exception