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‫Instructor: Hi, within this lecture,

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‫we're going to continue building our calculator app.

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‫So in order to do that,

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‫I'm going to write the first method over here,

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‫which is our sum method.

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‫So first of all, we need to get the strings

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‫or the numbers that our user has given as an input

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‫and we need to add them together

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‫and then finally, show the result

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‫in a text view in the result text to the user.

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‫We already have number1Text over here

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‫and we can reach it under sum method, right?

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‫Now, if I write something like this, number1Text,

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‫as you can see, there is a method called getText.

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‫And if you see the right side of it, it's editable.

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‫So this is kind of a custom class.

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‫It's not a string, it's not an integer,

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‫it's not a data type that we are familiar with.

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‫So you cannot edit,

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‫you cannot do what you can do with strings.

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‫It's a custom class but luckily,

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‫we can convert it to string.

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‫Now, we need to convert it into a string

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‫so that we can do something with it.

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‫We cannot do much with editable.

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‫So this is a class in our class created

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‫in order to write some text

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‫or get some text out of the edit text.

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‫So if you do that,

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‫you can see toString method over here.

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‫So this is what we are looking for.

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‫This is how we get strings out of the edit text.

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‫Now, I can actually make this equal

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‫to into something called myString, for example.

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‫And since this is a string,

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‫I can get the other string as well

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‫but I cannot add them together

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‫because they're not numbers, right?

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‫In order to do that, I can create some kind of an integer

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‫or a double or a float out of those strings.

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‫So you don't know how to do that.

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‫I'm gonna show you, don't worry.

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‫But you know, you get the logic, right?

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‫You cannot add two strings together,

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‫you can actually add them but it's nothing more

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‫than concatenating two strings together,

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‫like adding one next to each other.

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‫But this is not what I want to do.

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‫I want to add two numbers together.

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‫So I have to create a number out of this string,

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‫and you can actually convert one type into another

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‫if they are suitable, if they're a fit for each other.

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‫For example, if you have a string like five,

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‫you can convert it into an integer.

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‫So in order to do that,

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‫I'm going to use Integer class like this.

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‫So write Integer and if you say .parse,

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‫you can see parseInt method

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‫and it actually requires a string as a parameter.

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‫So this is what we are going to use.

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‫We're going to use this parseInt method

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‫and we're going to give our string as a parameter.

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‫It will convert our string into an integer.

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‫Okay? And we don't have to do that anymore.

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‫So let me delete everything from here,

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‫and start by writing Integer.parseInt.

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‫It will ask me for this string.

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‫I'm going to cut this from here.

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‫I'm not gonna take the semicolon,

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‫and add it over here.

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‫And this is what we're gonna use in order

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‫to get an integer out of our editText.

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‫So I'm going to assign this to a variable called number1.

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‫And of course, we can do that for number2 as well.

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‫Right?

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‫Since we have two numbers, this is number one.

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‫I'm gonna get the second one as well.

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‫Now, I'm gonna copy this and paste it over here.

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‫Change it to number two,

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‫and of course, I'm gonna change the text one as well

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‫so that I will have two numbers.

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‫Now, I can actually create a result integer

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‫and add them together like number1 plus number2,

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‫and hit semicolon.

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‫Here you go.

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‫Now I see the final result over here.

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‫Now, I can actually change the resultText

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‫by saying resultText.setText.

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‫And when you say setText,

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‫it actually asks for a string or a character.

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‫You cannot just come over here

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‫and give result as a parameter

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‫because it's an integer.

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‫It will look like it's working

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‫but it's gonna crash once you do that.

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‫So you have to convert this integer into a string.

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‫And luckily, we have a very good method in order to do that.

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‫Once you write something like this,

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‫write any string over here like this,

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‫you can add another integer

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‫or another float or another number

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‫and it will convert it into a string.

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‫Now this is okay.

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‫You can actually test this.

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‫So result plus result variable.

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‫Okay?

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‫So I'm going to test this on my emulator, okay?

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‫So I suggest you do the same thing as well.

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‫So open the emulator

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‫and just write some random numbers and hit them together.

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‫Here you go, result is eight.

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‫So we can try with other numbers like 13.

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‫Let's change it to 3,000, for example.

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‫Here you go. Now it's working.

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‫Of course, it's trivial to do the others as well.

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‫I'm just gonna copy them

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‫and paste them over here, okay?

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‫And paste them over here and paste them over here.

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‫So right now I can just change the sign

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‫like this is deduction,

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‫this is multiply and this is divide.

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‫Here you go.

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‫Now we are ready to test this.

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‫So we can see the other methods,

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‫other operations as well.

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‫So I believe we're coming to an end

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‫but actually, we have some more things to do,

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‫some more things to consider.

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‫So let me try this.

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‫So this is 12. This is eight.

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‫This is 20 and this is 5.

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‫So here you go, it's now working.

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‫Of course, we have some kind of issues in this app.

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‫Since we're doing this for a test,

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‫it's not very important

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‫but it's important to practice

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‫what we have learned so far.

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‫For example, if you just write your name

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‫for an input in your first edit text,

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‫if you click any of the buttons, it will crash.

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‫And whilst you see a screen like this,

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‫you can go to Logcat immediately

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‫in order to see why it's crashed.

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‫So if you go to error section,

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‫you can find the real error message

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‫that you're looking for.

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‫So here you go.

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‫One of the error messages.

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‫So it says that yeah, I cannot do this onClick because why?

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‫Because there is something wrong, as you can see.

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‫We have an input string of atil

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‫and we tried to cast this

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‫as an integer like Integer.parseInt

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‫and it won't work obviously

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‫because it's not a number, it's just a random string,

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‫a random text.

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‫So how do we overcome this problem?

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‫This is one of the things that we should actually consider

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‫when we make calculator or make any apps.

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‫So we're going to do that within the next lecture.