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okay i did want to go over something with you that i went over with you yesterday and i wanted to go over with you and go over it with you today but i figured i'd just make a video of it that way you can have this in your library of things you need to know about java programming particularly when you go to take the ap csa exam so to recall a couple days ago i was talking about methods where you pass you pass primitive types and they're copied versus methods where you pass objects by reference so let's explore the two and i went over this a couple days ago but i'll go over it again so notice here i declare an integer integer n is equal to 5 and i'm going to call that method pass by copied and there's that method there so n comes integer n and what i'll do is i'll add increment n by 10 and then i'll print it out once this method returns though this method has a copy of what was passed in does not have a reference so whatever effect i make to n will only be seen within this method once i leave it the value of n the initial value of n here will still remain 5. okay so when i run this it should print out 5 plus 10 is 15 and then i should print out 5 so let's see here oh yep so i printed out 15 because then came five and i added 10 and it printed 15 but when i came back it printed five so pads by copy primitive types are passed by copied now let's look at passing something passing something by reference here so here i am declaring an array of integers and now is a more appropriate time to talk about this because we're working with arrays okay so let me do this so now what i've done i have declared an array of integer type there's three elements in that array one two three i'm going to call this method pass by reference i am passing the array the integer array of j and then when i come out i'll print out the first element of that array so let's take a look at this method here so here's pass by reference so here's my integer array with a name of n so i'll i'll add to the first element 10 so let's see here so the first element up here was one so when i add 10 it should print out 11 but then when i come back and print out the first element again it should print out 11 because objects are passed by reference in other words whatever changes i make here and this method passed by reference will hold all right so here we go so there you go 11 11. difference between pass by copy primitives are copied and then objects are passed by reference now let's look at what i was going over today so i was talking about the for each loop and you cannot add or remove elements with a for each loop you cannot change values of elements with any for each loop whether they are primitive data types or references to objects you have no way to do that so let's look at okay so here um what do i do okay so what i'm going to do is i will declare an array of integers so integer summary it will have element zero one two three and then i'm going to call the method but first let me go ahead and and um okay comment that out so let's take a look at the method demonstrate some array so i'm using the for each loop right so n comes that array that integer array which i call n array and then i iterate through it so for integer value so that array is of has elements that are of integer so integer value will be how uh how i will reference each element in that array that i passed in okay so an array is the array that i passed in but notice here there's no way that i could change the element i could change in the value of what's in some array there's no way i can do that um you cannot change or remove i would have no way to remove or add elements can't change them not not within a for each loop can't do that there's no way i'd be able to do that but here and so maybe this is where you get your money's worth actually you don't spend money for this class but it does say here however you can change an object if it is mutable by calling a mutator method on that object and so what do we mean by a mutator method something that changes some property of that object getters and setters all right so here we go so i'll show you what that means all right so what i've done here so let me comment this out and then i'm going to uncomment this here okay so what i have done is i have created a a class called immutable object right there it's a mutable object and i have a private instance variable i have a constructor i'm going to pass in a value into the constructor and assign it to my instance variable and then i have a setter method okay i will um so this method here is the parameter will be some value i'll pass in and then i'll just add whatever i pass in to my instance um value to my property so incremented by whatever value i have and then i can also return the value that's stored in that object okay return a value so i have created a mutable object with getters and setters mutable so what do they say immutable mutate immutable mutator methods if you were unclear what they were talking if if you weren't clear what i said today all right so there's my so there's my class my mutable object now let me go back here all right so what i'm going to do so what i'm going to do i'm going to instantiate it create a immutable object reference variable object one and when i create that object i'll assign a value and that object five so let me go back here so a value will be five and i'll do i'll create another mutable object call it object two and then i'll assign a value of 10 and the immutable object object 3 and assign it a value of 20. and then what i'll do is i'll create an array of mutable objects okay so up here i have um mutable objects so notice here i have the i have those brackets there i'm creating an array of mutable objects an array down here 29 27 29 it's just one single mutable object but now i'm going to create an array of mutable objects and then so here so objects equals new mutable object and i'll create three of them all right i'll create three an array to hold three objects to hold three mutable objects okay and then so for the first element of that array i'll assign object one and then for this um next element i'll assign assign object to and then for the next element i'll assign object three so i have an array of mutable objects okay and each of those immutable objects have mutator methods setters and getters now so i'm going to call then this method here passing in my array of immutable objects demonstrate to so here's dentistry 2. now so n comes an array of mutable objects which i call array out array of objects and then for my for each method so mutable object and object remember each this array of mutable objects has not an array a mutable object in it so i have an array of mutable objects so mutable object and object in the array of objects array of objects okay again i'm working as i iterate through that array i'm working with just a mutable object and that array name is called an array of objects right but now notice here now i can actually change something about that mutable object by calling calling the mutator method or the setter method i can go in objects that change value see up here when i just set integer an array there's nothing i can do to change the value of that array that was passed in absolutely nothing but now here i can because i've created an array of mutable objects and i've created setter and gutter methods see the difference is this however you can change an object if it is mutable by calling a mutator method on that object all right so what so let's take a look at here that initially i gave the values of 5 10 and 20. so i'm going to add 50 to each value so i should have 55 60 and 70 when i return from this function here from demonstrate to all right so i call that function and then once i return i'll do another for each loop mutable object objects and then i'll print out i'll print out the value of each of those objects that was in that class i'll print out a value return a value and let's see here okay so let's see voila there you go 50 60 70. okay so that's what was meant by that there with any for each loop you cannot add or remove elements within them for each loop you cannot change values of elements even if their primitive types are referenced to object however you can change an object if it is mutable by calling a mutator method on that object right so i hope that clarifies anything there so