Exam coming up - Need to check some things

[überfuzz]

I'm trying to grasp what some stuff do.

public - this makes a class,method etc. open to the world, so to speak.
private - open to class it self.

static - info shared by all classes or methods.

Please comment this:

public class Object{
private var_1; //only visible within the class.
public var_2; //open to all classes 
public static var_3 //open to all classes, all objects of type Object share this info.
private static var_4 //only visible within the class, all objects of typ Object share this.
}

Same for methods etc, not just instance variables. Or?

[Petr]

It is access modifiers like public > protected > default > private. see Controlling Access to Members of a Class (The Java™ Tutorials > Learning the Java Language > Classes and Objects)
static is keyword for is used without a instance object.
final is keyword. It declare that variable can't re-instance.

[überfuzz]

Al right! So if I were to make some program calculating stuff I could do:

public static final double pi = 3.14;

final to prevent over writing it.
static to make every object sharing pi.

[DarrylBurke]

Yes, but that's a terrible value for π. And the java.lang.Math class already defines a much, much closer approximation that you can use.

db

[überfuzz]

I know, I just had to clarify the use of static final etc. :-)

[überfuzz]

By the way, this is all stuff I should know... :-)

The course is mostly recursive methods, Linked Lists, Binary threes, etc. Quite tricky to get it right, as we're writing code on paper. With the comp you always gets an error throned in your face if you mess things up.

[goldest]

I know, I just had to clarify the use of static final etc. :-)

By the way, static final are usually used when writing constant values. As per naming convention, that variable should be upper cased. Something like,

public static final double PI = 3.141592653589793;

Refer to naming convention here : Naming Conventions

Just an FYI as the exam is coming up

Goldest

[Petr]

static final are usually used when writing constant values

I read that now to make so is not advice instead it you can use enumerations. I read it in a book Effective Java by Johnny Block

[goldest]

I read that now to make so is not advice instead it you can use enumerations.

It depends on your requirement and design. I mean, if you have only a single or couple of constants then you can declare them simply the usual way.

You can have enums when the constants are related. Or you can even have your constants declared in the interface and then you can use them by implementing it. There may be other ways as well.

Goldest

[Tolls]

I read that now to make so is not advice instead it you can use enumerations. I read it in a book Effective Java by Johnny Block

PI as part of an enum makes no sense...

[JosAH]

Yes, but that's a terrible value for π. And the java.lang.Math class already defines a much, much closer approximation that you can use.

As all the religious people know that value equals 3; that truth can be found (coincidentally) in Kings 22:7 (<--- here!)

kind regards,

Jos

[überfuzz]

Constants written in capitals. I'll keep that in mind.

I'm brooding some things... about classes.

public abstract class Main{
  int instance_variable
  Object something;

  public Main(Object something){  //constructor
    this.something = something;
    this.instance_variable = 10;
  }

  public someMethod(){
    return instance_variable;
  }
}

public class Sub extends Main{

  public Sub(Object something){
    super(something);           //free loading mains constructor.
    //I can write more constructors here as long as I don't use Sub(Object), already taken.
  }

  public int someMethod(){
    //Is it possible to leave out methods that's situated in the Main class, even if main is abstract? 
    //Or do I have to write then here as well?
  }
}

I hope I'm making some sense here, baer with me.

[goldest]

Suggested reading : Abstract Methods and Classes and Defining Methods

Hope that helps,

Goldest

[DarrylBurke]

As all the religious people know that value equals 3; that truth can be found (coincidentally) in Kings 22:7 (<--- here!)

kind regards,

Jos

1 Kings or 2 Kings?

Oh, I see. I think you missed the i in Josiah

db

[überfuzz]

Exam today, I think I did all right.
My thanks to everyone who pitched in!