Reference

```
public interface Reference<T>
```
A very general purpose interface to provide a reference to an object that may or may not be available. Uses can range from allowing someone else to attach/detach the value, to calculating the reference on the fly.
Does not support null values, as null represents "not available". If you need to pass null, you should use a sentinel that extends from T to indicate the null condition.

- Method Summary
  
  All Methods Instance Methods Abstract Methods
  Modifier and Type Method Description
  
  T get()

- Method Detail
  - get
```
T get()
```
    Returns:
    
    the referenced object. Returns NULL if the reference is not available.