public and private members of a class

Question

Why can be private member of the class useful, if i cannot access it from outside? what can i do with it?

Answer 1

Say you have a class which counts numbers.

class Counter{
private int counter;
public Counter(){ counter = 0; }
public void count(){ counter++; }
public int getCounter(){ return counter; }
}

You'd use it like this:

var c = new Counter();
c.count();
c.count();
Console.WriteLine(c.getCounter()); // will print 2

Now imagine if that private `counter` variable were public! You could just set it to whatever you want and all your counting would be messed up and wrong. And in a way it's your fault, you allowed the `counter` variable to be messed with. The way to deal with it is to make it private - that's like saying "you don't need to know about `counter`, just use the `count` and `getCounter` methods" to the person who will be using your class.

Generally, try to make as many things private as possible - the less "surface area" your class has, the less a person using your class can screw up. If your class only has a few public members, you exactly know how your class will be used and what can and can't happen!

Answer 2

thank you, really clear and helpful answer:)