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welcome to section three working with

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akka basic tools in the previous section

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you learned the basic actor concepts in

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akka in this section we will take a look

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at the basic tools in occur such as

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actor f versus actor path versus actor

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selection routing replace actor behavior

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via become unbecoming

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via FSM let's start our first video

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actor ref versus actor path versus actor

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selection in this video we will discuss

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what's the difference between actor ref

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actor path and actor selection in the

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previous section when we discussed actor

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components we said that the actor ref is

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the interface of the actor instance

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actor F is a reference for a single

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actor it is created when an actor

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instance is created and is pointed to

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this instance when the actor is starts

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the instance still points to the same

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actor ref but when the actor shuts down

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the actor reference will point to a

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dead-letter and when you create a new

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instance

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acha will create a new actor reference

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this means actor references don't change

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during the actor life cycle we know

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actors are created in a strictly

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hierarchical fashion if we are thinking

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about an actor's tree like a file system

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and want to get a path for actor B it's

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a forward slash user /a /b this is a

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path for an actor actor path is a

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location of the actor on the actor

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system tree it's a sequence of actor

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names given by recursively following the

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supervision links between a child and

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parent down towards the roots of the

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actor system the difference between an

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actor path and actor ref is that the

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actor path represents a name of the

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actor which means you can create the

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actor terminate it and then create a new

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actor with the same path the newly

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created actor is a new instance of the

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actor which means it has a different

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actor reference actor selection is

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another representation of the actor like

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actor reference

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you can send messages to an actor via

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actor selection like actor F the main

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difference between them is that the

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actor selection is created from the

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actor path or actor name this means that

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the actor selection stays valid even

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when an actor dies and another instance

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is created so you can't watch the actor

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selection like actor reference because

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actor selection doesn't represent a

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single instance it represents a path now

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let's play with an actor reference and

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actor selection we have a counter actor

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that handles two messages increment and

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decrement and has a count variable now

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let's create an instance from a counter

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then let's print an act of reference for

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our instance after that let's create an

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actor selection we will use the actor

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selection method that takes a path or

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name we will give it our actor name and

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print the actor selection for our actor

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then let's kill our counter instance and

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create a new one and a new actor

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selection we'll print a new actor

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reference and actor selection let's run

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yeah it's not the same actor reference

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but it's the same actor selection we

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said we can't watch the actor selection

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but what if we don't have an actor

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reference and we know just a name for

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the actor how can we watch it it's

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simple by default every actor can handle

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a message called identify and reply to

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this message with the actor reference so

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you can easily convert active selection

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to act a reference and avoid using actor

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selection so let's create a watch actor

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that will have a selection value for the

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counter actor we will send an identify

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message for this selection an identify

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message contains the message ID that

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will return a response on the receive

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method we will handle the response of

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identify

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acta identify contains a correlated ID

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which is the message ID and an optional

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value for actor ref when the actor is

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live it will have some value for actor F

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and when the actor does not exist the

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value will be none

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you

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now let's create two instance forms

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counter and watcher let's run

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great that's the act of reference for

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the current running counter instance to

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summarize we discussed the difference

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between actor reference actor path and

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actor selection