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 AvailableVariables
```
A functional interface for obtaining the value of variables given their names.

Author:

Randall Hauch

Method Summary

All Methods Static Methods Instance Methods Abstract Methods Default Methods
Modifier and Type	Method	Description
`default AvailableVariables`	`and(AvailableVariables next)`	Obtain an `AvailableVariables` function that first checks this instance and then checks the supplied instance.
`static AvailableVariables`	`configVariables(Configuration config)`	Get an `AvailableVariables` that returns the value of a `Configuration property`.
`static AvailableVariables`	`empty()`	Get an `AvailableVariables` that always returns null.
`static AvailableVariables`	`environmentVariables(Configuration config)`	Get an `AvailableVariables` that returns `System environment variables` set with operating system environment variables (e.g., `${JAVA_HOME}`).
`static AvailableVariables`	`systemVariables(Configuration config)`	Get an `AvailableVariables` that returns `System properties` set with `-Dvariable=value`.
`String`	`variableForName(String varName)`	Obtain the value of a variable with the given name.

- Method Detail
  - configVariables
```
static AvailableVariables configVariables(Configuration config)
```
    Get an AvailableVariables that returns the value of a Configuration property.
    
    Parameters:
    
    config - the configuration
    
    Returns:
    
    the available variables function that returns the configuration property value for the given property name; never null
  - systemVariables
```
static AvailableVariables systemVariables(Configuration config)
```
    Get an AvailableVariables that returns System properties set with -Dvariable=value.
    This method does not use the configuration.
    
    Parameters:
    
    config - the configuration
    
    Returns:
    
    the available variables function that returns System properties; never null
  - environmentVariables
```
static AvailableVariables environmentVariables(Configuration config)
```
    Get an AvailableVariables that returns System environment variables set with operating system environment variables (e.g., ${JAVA_HOME}).
    This method does not use the configuration.
    
    Parameters:
    
    config - the configuration
    
    Returns:
    
    the available variables function that returns System properties; never null
  - empty
```
static AvailableVariables empty()
```
    Get an AvailableVariables that always returns null.
    
    Returns:
    
    the empty available variables function that always return null.
  - variableForName
```
String variableForName(String varName)
```
    Obtain the value of a variable with the given name.
    
    Parameters:
    
    varName - the variable name; may be null
    
    Returns:
    
    the value of the variable; may be null if the named variable is not known
  - and
```
default AvailableVariables and(AvailableVariables next)
```
    Obtain an AvailableVariables function that first checks this instance and then checks the supplied instance.
    
    Parameters:
    
    next - the next AvailableVariables instance to check
    
    Returns:
    
    the new AvailableVariables function that combines both instances; never null but may be this instance if next is null or

Interface AvailableVariables

Method Summary

Method Detail

configVariables

systemVariables

environmentVariables

empty

variableForName

and