Access modifiers, why?

[bubbless]

Hi

I've got a question about access modifiers.
I know what each modifier does, but I can't find when you have to use wich modifier.
Everyone says "use private, unless you can't", but why is that?

Thanks in advance,
Glenn

[travishein]

usually you would want to use private fields to hide the implementation details not relevant to something external. The idea, is the object is to perform a certain function, and the contract (our coupling) with the external 'world' should be done through methods to manipulate the state of the object.

see also: Controlling Access to Members of a Class (The Java™ Tutorials > Learning the Java Language > Classes and Objects)

[Eranga]

Hi

I've got a question about access modifiers.
I know what each modifier does, but I can't find when you have to use wich modifier.
Everyone says "use private, unless you can't", but why is that?

Thanks in advance,
Glenn

Yes, travishein gives you a better explanation. As he said the whole idea is hiding unnecessary details about your implementation to the outside. The following article may also helpful to you.

Introduction to Java Access Modifiers | Java Beginner

[JosAH]

I've got a question about access modifiers.
I know what each modifier does, but I can't find when you have to use wich modifier.
Everyone says "use private, unless you can't", but why is that?

Because you don't want your privvy parts to be fondled with by arbitrary others.

kind regards,

Jos ;-)

[bubbless]

And what if you are the only programmer of the project?
Is it necessary to make them all as restricted as possible?
And why would you make variables/methods that other programmers can't access?
I know the basics about it and who can access what but I'm trying to understand when to choose certain modifiers.

[JosAH]

And what if you are the only programmer of the project?
Is it necessary to make them all as restricted as possible?
And why would you make variables/methods that other programmers can't access?
I know the basics about it and who can access what but I'm trying to understand when to choose certain modifiers.

Even if you're the only programmer on the project: don't even trust yourself, you also make mistakes, no matter how small or how innocent; it's a good thing that your software protects you against your own mistakes.

A small example: suppose an int property needs to have an even value for the object to function properly. It is way better to make it a private property and implement a small setter method like this:

private int property= 0; // must be even

public int setProperty(int property) {
   if (property&1 == 1)
      throw IllegalArgumentException("property must be even: "+property)l
   this.property= property;
}

Suppose the property member variable would've been public; everyone, including yourself can do things like: myObject.propery= 41; and things keep on working for a little while and all of a sudden: crash, disaster and no stack trace indicating who or what did it ...

kind regards,

Jos