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‫Instructor: Hi.

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‫Within this lecture we are going to finalize

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‫our calculator app by making it into a Safe calculator.

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‫Now we get this error

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‫because we did give something odd over here

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‫like an apple or a till or any word rather than a number.

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‫Okay? So you can just try writing any words and it'll crash.

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‫If you don't give any numbers over here, it will crash.

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‫So one of the things that you may consider

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‫is to change this keyboard so that user will be able to

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‫only give numbers as an input, right?

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‫And there's a fine way to do that

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‫if you come over here to your activity main xml, okay?

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‫If you click one of the edit texts

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‫now you can find something called input type.

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‫If you cannot find it over here you can search it from there

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‫and you can find it on the right hand side like this.

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‫So find input type.

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‫And as you can see the current input type we have over here

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‫is the text person name.

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‫So this changes the keyboard.

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‫So we can make it for passwords, we can make it for emails

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‫we can make it for numbers as well.

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‫So make sure you check the numbers

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‫and uncheck the text person name.

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‫So the input type is only number right now.

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‫So it'll display the number keyboard.

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‫Of course, we are gonna have to do the same thing

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‫for the edit text two as well.

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‫So let me uncheck this,

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‫but once I unchecked that, it's disappears.

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‫So I'm gonna search it from here, okay

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‫input type and come over here and find the number.

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‫And I'm going to make it true

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‫so that it will display only the number.

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‫So here you go.

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‫I believe we are now okay to test this.

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‫So let me run this from scratch

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‫and let me go back into my coding section.

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‫So if you come over here

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‫and click one of the edit texts right now, as you can see

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‫we can only see the numbers right now.

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‫So I can give the inputs as I want.

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‫However, there's some still kind of an issue

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‫that we might need to consider like this.

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‫So if a user leaves it blank

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‫and just clicks one of the buttons it'll crash again

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‫because there won't be any input

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‫and it won't be able to convert it into a number or stuff.

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‫So it will crash again.

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‫So one of the things that we can do over here

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‫is to consider checking to see if the input is empty or not.

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‫So how do we do that?

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‫Of course, we can use an if control, if statement, right?

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‫Like we have seen before.

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‫So before we do everything over here,

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‫under some for example, we can check to see

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‫if this toString methods give us something

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‫like an empty string.

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‫And if that's the case, we're not gonna do anything else.

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‫For example, we can come over here

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‫and say if numberText.getText.toString

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‫and I believe you have a tendency to do like

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‫this double equal sign and then an empty string.

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‫And it's a very good thought, but it doesn't work in Java.

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‫It works in Kotlin, it works in Python.

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‫It works in Swift, but it doesn't work in Java

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‫because you cannot actually check to see

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‫if a string equals to some string with the sign

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‫but rather you have to say toString.matches, okay?

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‫So you check if the toString are the same

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‫or have the same content with this matches method.

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‫So once you do that,

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‫you can actually write whatever you want

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‫inside of this matches method like this.

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‫You can just add double quotation marks over here.

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‫It will search for a string, empty string.

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‫And if that's the case, we are not gonna do anything else.

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‫However, we only did it for number one text.

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‫Now we're gonna have to do it for number two texts as well.

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‫So we are going to use an OR open door here

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‫rather than ands,

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‫because either of this is true, then there's a problem.

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‫So we're going to say if number one text is empty

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‫or number two text is empty, then don't do anything.

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‫For example, you can do the pipe signs over here

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‫like we have seen before, and it means or

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‫and you can add number two text

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‫like number two text.getText.toString.matches"

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‫So let me close this down, and here you go.

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‫Now we are ready.

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‫So let me delete the space and open my curly braces.

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‫So if there is a problem,

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‫then we are going to display some kind of message.

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‫But else, if there is no problem,

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‫I'm going to cut everything from here and paste them here

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‫but for a reason, I cannot do that.

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‫Let me try one more time.

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‫Here you go, now I managed to do it.

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‫So if there is a problem, I'm not gonna do those

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‫but if there isn't one, then I'm gonna do those.

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‫And if there isn't any, there is a problem actually

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‫we can just use the result text.set text

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‫in order to give a message to the user

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‫like there is a no number, enter number, what are you doing?

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‫Something like this.

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‫Okay?

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‫So let me make this

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‫into an uppercase letter like this, and here you go.

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‫Now let's test this with some method.

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‫And if it works,

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‫of course the rest of the app will be trivial to complete

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‫like I'm gonna copy and paste everything.

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‫So let me try with 10

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‫or let me leave this blank and give 10 over here,

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‫and here you go.

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‫It says enter number.

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‫So if I write something like two or 20

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‫then it'll just do it.

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‫And if I leave number two blank as well

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‫I will get the error message.

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‫So let me copy this and let me delete everything

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‫under deduct and paste the new one and just change the sign.

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‫Okay, like this.

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‫And here you go.

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‫So let me do that for multiply

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‫let me just change design, and let me do that

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‫for the final method as well, which is divide.

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‫Come over here and change design.

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‫Here you go.

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‫Now I believe we completed our app.

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‫Let's try this.

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‫Of course, there are other things to consider

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‫if you are really developing a calculator for real world

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‫like if you just divide a number by zero

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‫it will cause some problems.

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‫Maybe you may want to check for that as well

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‫but I'm not gonna do that.

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‫We are just doing this as a practice.

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‫If you can always that problem's on the way,

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‫then I believe you can actually solve them

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‫by yourselves as well.

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‫So let me test this.

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‫Okay I'm gonna say 10 and leave those blank

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‫and as you can see, it says enter number

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‫but once I give some kind of input over here, like two

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‫then it will display the results.

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‫So now it works.

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‫And we have learned how to work with Java fundamentals.

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‫You have learned how to deal with problems,

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‫where to look at when you get a crash,

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‫and how to actually think

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‫consider the problems that may occur

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‫during the user input section

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‫and have some kind of preventive methods for that as well.

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‫This is how you deal with Java coding.

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‫This is how we deal with Android development in general.

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‫So I hope you enjoyed this section.

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‫Let's meet at the new one.