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‫All right.

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‫So now that you know how to use arrays and 2D arrays as well as for each loops, let's combine those

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‫let's combine the concepts in one video and one example, but also let's look at nested for loops.

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‫So in this video, we're going to go over these different features and then we will see when to use

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‫a nested for loop and what the advantages of a nested for loop over a for each loop are when it comes

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‫to, for example, multi dimensional arrays.

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‫Okay, so let's get started.

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‫The first thing that I have here is, as you can see, I have this matrix which is a two dimensional

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‫array which has three items towards each dimension, so three rows and three columns, so to speak.

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‫So I'm going to use the for each loop by using the for each keyword here this one and tab.

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‫And this will then allow me to basically just type in really quickly what type it is, how I want to

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‫call the item of the collection that I'm iterating through and the collection name.

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‫So this is a neat little trick if you want to become faster coding.

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‫So the item will be of type integer because we want to iterate through this matrix which has a bunch

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‫of integers in it and the item we can call it item, we could call it num because it's a number, we

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‫could call it element.

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‫This would be in normal names that you would see here, but item is going to be fine for now.

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‫And then the collection that I want to iterate through is going to be my matrix that I prepared up here.

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‫And that's also the reason why I needed to make this matrix static, because I'm using it inside of

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‫my static main method.

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‫And you cannot use non static items or variables inside of the static main method or inside of static

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‫methods in general.

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‫So in order to iterate forward through this for each loop and display the matrix items, we can just

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‫go ahead and use the console right line statement here.

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‫So see w double tab and here I'm just going to say display the item and then make an empty space.

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‫Or create an empty space and actually let's not use red line, but right.

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‫So this will just write it in one line and not create a new line all the time.

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‫Now, let's run this real quick.

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‫And we will see that we have one, two, three, four, five, six, seven, eight, nine.

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‫So all of the items that we have here in our matrix are being displayed.

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‫So we're using this for each loop to go through every single item inside of this matrix, and it just

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‫goes from left or top left to bottom right, so to speak, in our example here.

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‫Okay.

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‫So for each loop is a powerful tool.

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‫It allows us to go through a collection and a 2D matrix, a 3D matrix, however many dimensions you

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‫want to have.

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‫All of those are in the end just collections, because here we're using an array and an array is a type

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‫of a collection and this is what we needed to give the for each loop to iterate through.

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‫So it iterates through our collection matrix.

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‫So now we can go ahead and use this in order to show you how you could achieve this using a nested for

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‫loop.

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‫So the for each loop is super useful if you just want to go through every single item in it, but it

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‫has certain disadvantages in terms of certain situations.

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‫So in the case that you want to now change the item, you cannot do it because it's protected.

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‫So you cannot go ahead and say item should now be overwritten with three, for example.

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‫As you can see here.

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‫So if you try that it says cannot assign to item because it is a for each iteration variable.

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‫So it's not the actual item, it's really just the value storage, so to speak.

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‫So we store whatever value we are currently looking at from our collection and what we store it here,

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‫the value of it.

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‫So in the first iteration, it's one.

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‫In the second iteration it's two, but it's never actually the the value itself, it's only a reference

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‫to the value.

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‫So this really doesn't help us.

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‫So if we want to actually adjust it, we would need something like a nested for loop.

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‫So here, let's go ahead and create a next for loop.

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‫I'm going to add a little bright line statement here saying this is printing our array using a nested

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‫for loop.

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‫So what is a nested for loop?

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‫Well, it's basically a for loop with another for loop inside of it.

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‫Okay.

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‫So here we're going to use four and we can use double tap again.

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‫So we go from I zero to the length.

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‫So here we need to enter the length of the iteration.

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‫So what I'm going to do here is I'm going to use my matrix, but I could of course use length here and

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‫this would then give me the length of the entire matrix.

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‫So basically the number of items that I have inside of this matrix, but that's not what I want.

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‫I want to go through each dimension, so I want to go through it row by row and column by column.

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‫So the first dimension will be the rows.

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‫So I can use a method that arrays offers.

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‫So the array class has this get length method where I need to pass the dimension.

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‫So this will get me the number represented or just you can see here that represents the number of elements

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‫in the specified dimension of the array.

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‫So in my case, if I enter zero, this will now return the zero dimension, which basically means the

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‫rows.

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‫So this will give me the rows.

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‫So now if I want to iterate through each individual column, I need to use another for loop in here.

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‫So this will be my inner for loop like so inner or loop.

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‫And this one out here.

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‫This is going to be the outer for loop.

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‫Okay.

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‫So.

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‫What we now need to change, of course, is going to be the iteration variable name.

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‫So here we are going to use J instead of I.

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‫That is a common practice.

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‫So if you have an inner for loop, you usually use J here as to counter variables name.

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‫But now we want to compare J not to the length of the first dimension, but of the second dimension.

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‫So we enter one here.

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‫So this will now allow me to go through every single column.

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‫So this for loop job will be to go through the individual columns and this for loops job will go through,

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‫the whole will be to go through the individual rows.

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‫So that means that we can now go ahead.

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‫And just do our right statement right here.

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‫But then, of course, we don't have an item here.

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‫So what do we have?

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‫Well, we have the matrix, the static variable that we created up here.

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‫But this matrix, it needs to know which items it should display.

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‫So I'm going to say just display I j which means display the F.

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‫Row at the J.F. column, which basically means in the first iteration, this I will be zero.

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‫And then we start with this for loop and this four loop will go through it until it's done, and then

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‫it will only go to the next iteration of the outer for loop.

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‫So only then I will be incremented by one.

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‫So that means I is going to stay zero until we've gone through this for loop, which means we start

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‫at zero for I and then we have J being zero in the first iteration.

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‫So we get the first entry, then we have J being one because we incremented once we ran through this

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‫line of code and we increase it by one.

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‫So now J is going to be one and we say zero one.

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‫So the position zero one of our matrix is going to be this two here, then J is going to be two, which

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‫will be this three.

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‫And then we check is.

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‫Two plus one, which is going to be well, j being incremented after the iteration is three less than

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‫the length of that current dimension that we're looking at.

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‫And the dimension is going to be the column dimension.

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‫So how many columns do we have?

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‫And in this case we have three columns.

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‫So three is not less than three, which is why this followup will be done with its execution.

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‫And we go to the outer for loop again.

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‫So this time we increase our increment i.

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‫By one, which means I will now be one.

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‫And then we go through this for loop three times again.

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‫So we have I being one and J being zero in the first iteration of this inner for loop.

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‫Then it will be one, then it will be two.

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‫So it will basically go through this item, then this item, then this item, and each time it will

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‫write it onto the console and leave an empty space.

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‫And then in the third iteration of our for loop or out of the loop here, it will go through the last

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‫row, so to speak.

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‫So this here is a nested for.

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‫Loop.

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‫Okay.

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‫So let's run this real quick just to see if this is actually going to do what I'm saying.

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‫And you can see here.

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‫Well, maybe I should print it slightly differently.

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‫Here.

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‫I'm going to have another line break.

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‫Like.

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‫So let's try this again.

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‫So you see, this is our 2D array printed using the nested for loop.

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‫This is this one here.

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‫This one was the for each loop.

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‫And now at this point, you might say, hey, what's the advantage, Dennis?

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‫Does this even make sense?

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‫I don't like what you're doing there.

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‫I prefer to use the for each loop.

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‫You see, it's super simple, very little bit of code that I required.

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‫Well, the cool thing here is I have directly access to the item that I'm currently looking at.

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‫So here in this case, I'm just iterating through it.

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‫But what if I would go ahead and assign a new value to it?

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‫Let's say I assign zero to it.

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‫So now if you run this, we will get a bunch of zeros.

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‫Here, you see 0000.

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‫So now I can create a logic with which I would, for example, overwrite the value, and that is not

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‫easily achievable with it for each loop.

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‫For each loop is super great.

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‫You just display something and run some code for every single item, but not specifically changing the

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‫item itself because the item is just a short term storage location for whatever value we have inside

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‫of the.

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‫Collection that we're looking at, and that's different for a nested loop, and that's already one advantage

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‫that you see here.

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‫But there are other advantages.

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‫And we're going to look at some more examples of nested for loops with this particular example that

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‫we have here.

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‫We're going to adjust it a little bit in the next video, and you are going to, for example, see how

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‫you can get even numbers or odd numbers from your for loop and then also see how you can adjust it so

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‫that you only print, for example, diagonal elements.

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‫Because this will give you a general idea of what you can use for loops for or nested for, loops for.

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‫And basically you have so much freedom in programming and I just wanted to give you some more tools

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‫that you can use.

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‫So at this point I'd say let's go over to the next video where we are going to look at that.