question about what makes a class public

[Janeice DelVecchio]

So I need to create a public class for this project I'm working on for school.

My question is, aren't ALL classes public unless declared private (like instance variables)?

Another facet to this question is.... can I have private instance variables in a public class?

Thanks a lot,
Janeice

[Ruben Guillen]

Dear Janeice

1) if we are talking about non-inner classes, normally classes could have only two possibles access modifiers: public and none (which indicates as default access).

There is a restriction of the compiler that only one public class could be defined per physical file with the extension java and the name of the file should be equal to the name of the public class, if there is not any public class inside the file then this restriction does not apply.

2) instance variables (no local variables) could have one of the following access modifier public, protected, none (default), private.

Regards.

[John de Michele]

My question is, aren't ALL classes public unless declared private (like instance variables)?

Nope, all outer classes are set to the default access unless declared public. Having a private outer class isn't meaningful, since you could never reach it. Inner classes can be private (or otherwise).

John.

[Janeice DelVecchio]

So..... (I deleted all the functional code here and left the declarations)

 //import libraries here

public class Student {		// putting "public" here is all I have to do, and make sure the filename is Student.java
		
	// private instance variables can go here
					
	void setName (String last, String first) {
	}	
		
	String getName (){
	}
		
		
	void setGrade (int score){
	}
	
	int getGrade () {
                }
				
	void createArray(String fileName) {
	}
	
	ArrayList<Character> getArray() {
	}
}
			
  

..... and everything will continue to work as is? REALLY??? Ummm..... the answer seems too simple here. Do I change anything in the way I refer to any of these methods or instance variables?

Thinking this should be harder,
Janeice

[John de Michele]

Janeice:

You probably want to make your member variables private (right now they're at the default access level), and your methods public (if that makes sense). Declaring a class public only affects that class, and not the methods or member variables.

John.

[Janeice DelVecchio]

John de Michele wrote:Janeice:

You probably want to make your member variables private (right now they're at the default access level), and your methods public (if that makes sense). Declaring a class public only affects that class, and not the methods or member variables.

John.

John, thanks
So it needs to look like this?

 //import libraries here   
  
public class Student {      // putting "public" here is all I have to do, and make sure the filename is Student.java   
           
    // private instance variables can go here   
                       
    public void setName (private String last, private String first) {   
    }      
           
    public String getName (){   
    }   
           
           
    public void setGrade (private int score){   
    }   
       
    public int getGrade () {   
                }   
                   
    public void createArray(private String fileName) {   
    }   
       
    public ArrayList<Character> getArray() {   
    }   
}   
  

.... and NOTHING needs to be done to the other existing classes?


--Janeice

[Ruben Guillen]

Dear Janeice

Please give a look here for information on access modifiers.

Regards.

[John de Michele]

Janeice:

You need to remove the access modifiers from the arguments to your methods, since that doesn't make sense. Other than that, you should be good.

John.

[Janeice DelVecchio]

John de Michele wrote:Janeice:

You need to remove the access modifiers from the arguments to your methods, since that doesn't make sense. Other than that, you should be good.

John.

Hehehe.... when you said "member variables" I thought you meant the argument variables. I didn't have my instance variables listed and you said my "member variables... [were] at default access." Inferring that got me in trouble.

Thanks.
Janeice

P.S. Thanks for the link Reuben!

[John de Michele]

Janeice:

Sorry about that. I was actually referring to your original statement that member variables are automatically set to private. Arguments are the variables that go into method signatures. Member variables are instance variables.

John.

[Janeice DelVecchio]

When I said:

My question is, aren't ALL classes public unless declared private (like instance variables)?

I meant...

"Instance variables are public unless declared private. I haven't been declaring my classes 'private,' so that leads me to believe my classes are ALREADY public."

I am so glad we cleared this up.
Janeice

[John de Michele]

Janeice:

LOL

John.

[Greg Stevens]

Janeice DelVecchio wrote:
I meant...

"Instance variables are public unless declared private. I haven't been declaring my classes 'private,' so that leads me to believe my classes
are ALREADY public."

Class members declared with no access modifier are package-private. This is different than public in that such members could be
accessed by other classes in the same package, but not by other classes in other packages.

[Janeice DelVecchio]

I haven't started using packages yet... I figured they were public when I could use any main method with any of the classes I made......

Bad assumption....

Janeice