Callback

Functional Interface:

This is a functional interface and can therefore be used as the assignment target for a lambda expression or method reference.
```
@FunctionalInterface
public interface Callback
```
A generic functional interface that is more semantically sound than Runnable. Use anywhere you wish to have a generic callback function.

Method Summary

All Methods Static Methods Instance Methods Abstract Methods
Modifier and Type	Method	Description
`void`	`call()`	The method that will be called.
`static Callback`	`dummy()`	Creates a dummy callback function.
`static Callback`	`dummyIfNull(Callback c)`	Returns the given callback object if it is not `null`.

- Method Detail
  - dummy
```
static Callback dummy()
```
    Creates a dummy callback function. This is useful to avoid using null.
    
    Returns:
    
    a dummy callback function
  - dummyIfNull
```
static Callback dummyIfNull(Callback c)
```
    Returns the given callback object if it is not null. Otherwise, a dummy() callback is returned. This is useful to avoid using null.
    
    Parameters:
    
    c - the callback function to check for null
    
    Returns:
    
    a non-null callback function
  - call
```
void call()
```
    The method that will be called.