CB this Keyword Quiz Q1 and GOOD CH5 tips

class Item
{
	private int ID;
	public Item (int id)
	{
		// constructor
		ID = id;
	}
	public int getID()
	{
		return ID;
	}
	public void addToCollection (ItemCollection c)
	{
		// c here is NOT related to the code segment A, JUST a parameter name that happens to overlap
		c.addItem(this);
		/*
		 * calls the addItem method by using its class(ItemCollection)'s object, c
		 * "this" = inserts the Item object (i and j in code segment A) into addItem
		 * = self-insert Item object into anther class ItemCollection's method: addItem
		 */
	}
}
class ItemCollection
{
	private int last_ID;
	// doesn't have any constructors = default constructor
	// the object c in code segment A also uses default constructor
	// meaning that last_ID is equal to null (0) in the following steps of addItem method
	public void addItem (Item i)
	// takes Item i as a parameter, NOT related to the code segment A, JUST an overlapping parameter name
	{
		if (i.getID() == last_ID)
		// uses the getID method in class Item using Item object i to return ID
		// compares i's ID to last_ID (at first empty because default constructor)
		// so, last_ID would be 0 in ItemCollection object c in code segment A
		{
			System.out.print("ID " + i.getID() + " rejected; ");
		}
		else
		// if the ID of class Item's object i is NOT equal to the last compared ID, accept
		{
			last_ID = i.getID();
			System.out.print("ID " + i.getID() + " accepted; ");
		}
	}
}


//////code segment A (written in a separate class other than Item or ItemCollection
// prints "ID 23 accepted; ID 32 accepted; ID 32 rejected; ID 23 accepted;"
class Main{
	public static void main(String[] args) {
		Item i = new Item(23);
		Item j = new Item(32);
		ItemCollection c = new ItemCollection();
		i.addToCollection(c);
		// AFTER it finishes every step in Item and ItemCollection back and forth, move on to next line
		j.addToCollection(c);
		j.addToCollection(c);
		i.addToCollection(c);
	}
}



// additional info from quiz:

/// static can be updated in different objects's methods and keep its updated value

//// static methods can access/update static variables but not instance variables

///// do not make a parameter name overlap with a pre-existing instance variable

////// don't declare the dataType of an instance variable except in the first initialization step
////// because it will be recognized as a local variable not instance variable

/////// printing an entire object will look for a .toString method (can be separate or attached)
/////// usually it will be written as a separate method, returning String
/////// if .toString isn't specified, will print some jibberish

//////// a method w return type other than "void" MUST have a return value for every possible outcome

///////// getValue should have same return dataType as the value