Question

I have simple but stupid question. We use access modifiers in Java to access variables in a Class. I do not understand that if we can access a private class variable outside the class using properties defined in public class, then what is difference between public and private? It is still accessible outside private class. I do not understand the concept of this public private concept.

Answer 1

If I understand your question correctly, you are asking why someone would write this:

public class MyClass {
    private int value;
    public int getValue() {
        return value;
    }
    public int setValue(int val) {
        value = val;
    }
}

instead of simply:

public class MyClass {
    public int value;
}

The main reason is to hide the internal structure of MyClass from client code. The benefit is that this allows you to more easily modify the internal structure of MyClass. Perhaps, for instance, you decide that another field in MyClass needs to be updated whenever value changes. This would be very difficult to implement without error if accesses to value were scattered everywhere in your code (and nigh-on impossible if your code served as a library for someone else’s code).

Additional benefits are that you can, if necessary, rewrite getValue() and setValue(int) to synchronize access to the value, to log writes to value, or do any number of other things.