Java Lesson 5 | Loops

I'm a special guest on Mac Heads 101, and this is going to be my fifth Java tutorial. Today, I'm going to be talking about loops. So, I'm not really going to be making like a program with you right now; I'm just going to be demonstrating loops. Later, we'll be making a program that involves loops, so um, in another tutorial.

So, basically, what a loop is, is it allows us to execute a certain block of code a certain number of times in a row. The first one I'm going to show you is called a while loop. To do this, you type while (condition) and then you give it a condition. By the way, I'm going to make a variable so I can actually test a condition. So, say int i = 0;

So, while i is less than 20, do this. Now, of course, since 0 is less than 20, it's always going to be going. It's going to go indefinitely. But if I put i++, which, by the way, is another way of writing i = i + 1, that will add 1 to i every time the loop goes around, which means eventually it'll no longer be less than 20, and the loop will stop.

Okay, so, while i is less than 20, it's going to do this, and it's going to add one every time it loops. So, it's going to do this while i is 0 through 19, and I'm just going to print out i. So now, if I run this, it's going to print out the value of i each time it loops through, which was zero, and then it looped again and added until 19.

I'll show you that i = i + 1 will do the same thing. And there we go, it does the same thing. So, what that does is, like, i, let's say 0 = 0 + 1, so now it equals 1. Then it's going to loop through with it equaling one. So that's the while loop.

Now, I'm going to make a for loop, and the for loop has three things in it. So, I just had a condition: for (int i = 0; i <= 20; i++). So now, I'm creating the variable in here. Then my condition, i is less than or equal to 20; semicolon i++, and then System.out.printLn(i);.

So, that would print; that would do the exact same thing except, yeah, it goes up to 20 because I did equal to or less than. That, um, says i = 0, there's the condition i is equal to or less than 20, and i++ is just like the last one.

I'm only going to be covering those two types of loops in this tutorial, but the last thing I want to mention is called um, a nested loop. So, I'm just going to make um, two loops to demonstrate this. A nested loop is a loop in a loop, so what happens is, um actually, if I make it less than 20, it's going to do this: while (i < 5).

And then, a loop in a loop, I'll just call this int x = 0;, and as long as x is less than 20, x++, right? And then just put nothing in there or actually, yeah, put something: System.out.print(x);.

So, what this is going to do is every time it runs this loop, it's going to run this loop. So, it's going to do this until x is um, 4, because that's 1 less than 5. Until x equals 4, it's going to execute this loop. So, it's going to execute it once: as x = 0, as x = 1, as x = 2, as x = 3, as x = 4.

And so you'll see it will execute it um, this loop that number of times. See, there we go, and it did it again. All right, so those are the loops.

I'm sorry if I went a little fast um, I'll try to go slower in the next tutorial. But, um, see you next time!