WEBVTT

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In this demo I'm going to show you how to make an object

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perform it's actions by calling it's methods.

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I have a bicycle object, created as we saw in the last demo

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and I'm going to inspect that object so that we know

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what the properties of the object are to begin with, 

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so we have pedalRpm zero, gear one

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wheelDiameter zero point five and five gears

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to see what actions an object can do

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we can right click on the object in the object bench

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and this shows us a menu with a list of the methods

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that are available for this object.

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The first thing I want to do is to start pedalling the bicycle

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to make it move or at least to model this happening

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I can call the method setPedalRpm to do this

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so I click on that option in the menu

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and I see a dialog box the method call dialog box

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and thats asking me for some information

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about how to do this, what pedalRpm value

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would I like to set, this is a

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parameter of the method is some information that the

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method needs in order to do the action

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or for the object to do the action

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we'll give that a value of three hundred.

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I can now inspect the object

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and you can see that the pedalRpm

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property has changed value to three hundred

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so I wonder how fast the bicycle is going now

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well I can ask the bicycle to tell me

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if I look at those methods again, it has a method called

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speed and that's going to calculate how fast bicycle is going

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and it's going to tell me the result of that

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this method unlike the setPedalRpm one

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doesn't need any information

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in order to perform the action.

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What it does instead is it returns a result

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it gives me back an answer so lets click on that

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that pops up a different type of dialog box this is a

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method result dialog box

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and that gives me the result of calling the method

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and it tells me that the speed is seven point eight five.

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The speed of a bicycle depends on 

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how fast it's being pedalled

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and also on what gear is selected

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so the bicycle object

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is another method that lets us

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change the gear

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I'm going to call the change gear method

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and up pops a method call dialog

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changeGear is a little bit different

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from setting the pedalRpm

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on most bicycles

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you change gears sequentially, to get from gear one

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to gear three you have to go through

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gear two and so on

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so we really only have two choices here 

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for changing gear do we change

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up or do we change down.

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there's some commentary here in the 

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dialog box that tells us that

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if we put in a value zero here

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that means we're changing down

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if we put in a value one, we're changing up

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so lets try a value of one,

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and lets inspect the object to see whats happened

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and we can see that the gear

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value has changed from one to two.

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Changing gear should have an 

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effect on the speed of the bicycle

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so lets call the speed method again

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and we get a different result showing that

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the bicycle has speeded up because we changed gear.

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What happens if we keep changing gear

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well lets call changeGear again

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and again enter one so we change up

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and inspect

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and we're now in gear three

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lets do that again

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again changing up

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inspect again and we are in gear four

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and one more time change gear up again

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and inspect again gear five

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and one more time, lets keep trying to change up

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change gear up

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and inspect again, and we're still in gear five

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so that last time we called changeGear

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and request it to change up

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it didn't actually change and thats because

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this bicycle only

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has five gears so it doesn't make sense

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to be able to change

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to a gear any higher than gear five.

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If I changeGear again and change down

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however that should be possible

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so lets see if thats happened

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inspect and yes the gear has gone back down to four.

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What do you think would happen

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if I kept changing gear down repeatedly?