Explaining access levels and visibility in OOP While teaching OOP in a high school CS major (in java), it is important (and part of the curriculum in any case) to explain &quot;what is the meaning of this public and private?&quot; (A question voiced by many students).
The usual explanation is a technical one:

Something public is accessible from anywhere.
Something private is, well, private.
protected ??
default access (when no other access modifier is given).

As for protected, the students know about inheritance but the explanation of &quot;it can be accessed by things down the inheritance tree&quot; doesn't really get the idea through. Examples only show it so far and only works for a number of students.
So this got me thinking: How can access levels be explained in an intuitive way to high school students?
Note: I'm not only asking about protected, that is my main problem when explaining access levels.
Clarification
I am talking about access modifiers for objects and methods, not classes:
public class Example extends JFrame{ //the public in this line is not what I'm asking about.
    private int x; //this is the kind of private asked about
    protected void paintComponents(Graphics g){ //and this is also the kind being asked about.
Here's an analogy that I've used for several years, and that students seem to understand. It doesn't focus on the rules, but why we have public and private and protected.

"Most of you know that I live down at the beach. If you find yourself riding past my house, and it's hot outside, you might come to my front door, knock and ask if you could have a soda. I don't live in a gated community, so anyone can come to my front door and knock. My front door is public. However, you can't open the front door, walk right in to my kitchen, open the refrigerator door, and help yourself to a soda! My refrigerator door is not public.

My children and grandchildren, however, who live next door, think nothing of walking into the house and getting anything they like out of the refrigerator. In our house, the refrigerator is protected; my family can directly access it, but the general public cannot.

Not everything in our family is protected, though. My kids know that going upstairs, finding my Visa card, and charging a new book at Amazon, isn't permitted. My Visa card, and the contents of my wallet, are private. No one else can access them directly; they have to make a request."