com.amazonaws.services.simpleworkflow.flow.core

Class Settable<V>

java.lang.Object

com.amazonaws.services.simpleworkflow.flow.core.Promise<V>

com.amazonaws.services.simpleworkflow.flow.core.Settable<V>

Type Parameters:

V - The type of value accepted and returned by this Settable.Use Void to represent Promise that indicates completion of operation that doesn't return a value.

public class Settable<V>
extends Promise<V>

It is an implementation of Promise, which exposes an additional set(Object) and chain(Promise) methods. Calling set(Object) puts it in ready state, with value retrievable through get() method. chain(Promise) links state of this Settable to another Promise. When another promise changes its state to ready the chained one is also becomes ready.

Use settable.set(null) to set Settable<Void> to the ready state.

Settable is frequently used to return data from code contained in anonymous classes. For example:

 
 Promise<Integer> foo() {
     final Settable<Integer> result = new Settable<Integer>();
     new TryCatch() {
                            
         protected void doTry() throws Throwable {
             Promise<Integer> activity1Result = activities.callActivity1();
             result.chain(activity1Result);
         }
                            
         protected void doCatch(Throwable e) throws Throwable {
             Promise<Void> handled = handleFailure(e);
             rethrow(e, handled);
         }
      };
      return result;
 }
 
 

Constructor Summary

Constructors

Constructor and Description
Settable()
Settable(V value)

Method Summary

Methods

Modifier and Type	Method and Description
protected void	addCallback(Runnable callback) Compliant implementation should notify callbacks after promise is set to ready state.
void	chain(Promise<V> chainTo) Used to chain this Settable with the passed in Promise.
V	get()
String	getDescription()
boolean	isReady()
protected void	removeCallback(Runnable callback)
void	set(V value)
void	setDescription(String description)
String	toString()
void	unchain() Used to unchain this Settable from the Promise object passed in last invocation of chain.

Methods inherited from class com.amazonaws.services.simpleworkflow.flow.core.Promise

asPromise, Void

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

Settable

public Settable(V value)

Settable

public Settable()

Method Detail

get

public V get()

Specified by:

get in class Promise<V>

Returns:

The value passed in when set() is called

Throws:

IllegalStateException - If set() is never called for this instance of Settable

isReady

public boolean isReady()

Specified by:

isReady in class Promise<V>

Returns:

true if set() is called for this Settable

set

public void set(V value)

Parameters:

value - Object to return when get() is called for this Settable. Use null to set Settable<Void> to the ready state.

Throws:

IllegalStateException - if the Promise is already in ready state

chain

public void chain(Promise<V> chainTo)

Used to chain this Settable with the passed in Promise. This allows the Settable to be ready whenever the passed in Promise is ready and the value for the chained Promise can be retrieved by calling get() method on this Settable.

Parameters:

chainTo - Promise object to chain this Settable to. Chaining to null equates calling set(Object) with null argument.

Throws:

IllegalStateException - if Settable is already in ready state or it is already chained to some other Promise

See Also:

unchain()

unchain

public void unchain()

Used to unchain this Settable from the Promise object passed in last invocation of chain. There is no requirement to unchain unless there is a need to chain the Settable to another Promise. Such need usually appears when implementing recursive functions or in TryCatchFinally.doCatch(Throwable) blocks. It is safe to call unchain if chain is never called for this Settable.

Throws:

IllegalStateException - If the Promise it is chained to is already in the ready state

addCallback

protected void addCallback(Runnable callback)

Description copied from class: Promise

Compliant implementation should notify callbacks after promise is set to ready state.

Specified by:

addCallback in class Promise<V>

Parameters:

callback - callback to notify

removeCallback

protected void removeCallback(Runnable callback)

Specified by:

removeCallback in class Promise<V>

getDescription

public String getDescription()

Overrides:

getDescription in class Promise<V>

Returns:

human friendly description on what this promise represents. Emitted for example as part of AsyncScope.getAsynchronousThreadDumpAsString()

setDescription

public void setDescription(String description)

Parameters:

description - human readable description of what this Promise represents.

See Also:

Promise.getDescription()

toString

public String toString()

Overrides:

toString in class Object