SetFromFlag (Apache Brooklyn)

```
@Retention(value=RUNTIME)
public @interface SetFromFlag
```
Annotation to indicate that a variable may be set through the use of a named argument, looking for the name specified here or inferred from the annotated field/argument/object.
This is used to automate the processing where named arguments are passed in constructors and other methods, and the values of those named arguments should be transferred to other known fields/arguments/objects at runtime.
Fields on a class are typically set from values in a map with a call to FlagUtils.setFieldsFromFlags(java.util.Map, Object). That method (and related, in the same class) will attend to the arguments here.

Optional Element Summary

Optional Elements
Modifier and Type	Optional Element and Description
`java.lang.String`	`defaultVal` The default value, if it is not explicitly set.
`boolean`	`immutable` whether the object should not be changed once set; defaults to false
`boolean`	`nullable` whether the object is required & should not be set to null; defaults to true.
`java.lang.String`	`value` the flag (key) which should be used to find the value; if empty defaults to field/argument/object name

- Element Detail
  - value
```
public abstract java.lang.String value
```
    the flag (key) which should be used to find the value; if empty defaults to field/argument/object name
    
    Default:
    
    ""
  - immutable
```
public abstract boolean immutable
```
    whether the object should not be changed once set; defaults to false
    this is partially tested for in many routines, but not all; when nullable=false the testing (when done) is guaranteed. however if nullable is allowed we do not distinguish between null and unset so explicitly setting null then setting to a value is not detected as an illegal mutating.
    
    Default:
    
    false
  - nullable
```
public abstract boolean nullable
```
    whether the object is required & should not be set to null; defaults to true. (there is no 'required' parameter, but setting nullable false then invoking e.g. FlagUtils.checkRequiredFields(Object) has the effect of requiring a value)
    code should call that method explicitly to enforce nullable false; errors are not done during a call to setFieldsFromFlags because fields may be initialised in multiple passes.)
    this is partially tested for in many routines, but not all
    
    Default:
    
    true
  - defaultVal
```
public abstract java.lang.String defaultVal
```
    The default value, if it is not explicitly set.
    The value will be coerced from String where required, for types supported by TypeCoercions.
    The field will be initialised with its default value on the first call to setFieldsFromFlags (or related). (The field will not be initialised if that method is not called.)
    
    Default:
    
    ""

Annotation Type SetFromFlag

Optional Element Summary

Element Detail

value

immutable

nullable

defaultVal