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Question regarding methods and classes

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  Question regarding methods and classes Linus Flustillbe <admin@nacs.dyndns-office.com> - 2011-10-23 03:28 +0000
    Re: Question regarding methods and classes Peter Duniho <NpOeStPeAdM@NnOwSlPiAnMk.com> - 2011-10-22 20:44 -0700
      Re: Question regarding methods and classes Patricia Shanahan <pats@acm.org> - 2011-10-23 06:14 +0100
    Re: Question regarding methods and classes markspace <-@.> - 2011-10-22 22:12 -0700
      Re: Question regarding methods and classes markspace <-@.> - 2011-10-22 22:14 -0700
        Re: Question regarding methods and classes Linus Flustillbe <admin@nacs.dyndns-office.com> - 2011-10-23 13:32 +0000
          Re: Question regarding methods and classes markspace <-@.> - 2011-10-23 07:43 -0700
          Re: Question regarding methods and classes Lew <lewbloch@gmail.com> - 2011-10-23 08:54 -0700
    Re: Question regarding methods and classes Roedy Green <see_website@mindprod.com.invalid> - 2011-10-23 01:37 -0700
      Re: Question regarding methods and classes Linus Flustillbe <admin@nacs.dyndns-office.com> - 2011-10-23 13:49 +0000
        Re: Question regarding methods and classes Roedy Green <see_website@mindprod.com.invalid> - 2011-11-02 01:23 -0700
    Re: Question regarding methods and classes Linus Flustillbe <admin@nacs.dyndns-office.com> - 2011-10-23 09:11 +0000

#9100 — Question regarding methods and classes

Does a method have to be part of a class that gets instatiated or can it
live in a class to be available to all other classes without
instantiation...it's available when it's imported?

I created a package called helperClasses and a class like this

package helperClasses;
public class rType {
	public boolean isBetweenInt(int a, int b, int c)
	{
		return (a <= c && a >=b);
	}
	public boolean isBetweenDouble(double target, double lower, double upper)
	{
		return (target <= upper && target >= lower);		
	}
}

Is there a way to make the methods contained in rType avaiable by simply
importing the class or does it have to be instantiated?  I'd like to be
able to, in a Java program, execute the following lines

import helperClasses;

public class test {
  public static void main(String[] args) {
    boolean isBetween = inBetweenInt(4,6,87);
    System.out.println(isBetween);
}
}


In this case, it would say "false"

Here is my working tester

import helperClasses;

class rTypeTest {
  public static void main(String[] args) {
// TODO Auto-generated method stub
   rType myTest = new rType();
   boolean hello = myTest.isBetweenInt(4,6,87);
   System.out.println(hello);
}
}

And actual output

false

Just seems like extra work and..even worse... if you create an instance
of rType and it has 250 methods, isn't that gonna potentially slow
things down.

So basically what I want to do is create a whole bunch of methods, put
them in one class and have them all available on demand just by
importing the class...no instantiations required.
Make sense?   This is probably silly so if it is, just ignore me..I'll
go away

-- 
****************************************************************
* Usenet Impovement Project http://nacs.dyndns-office.com/usenet
****************************************************************

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#9101

On 10/22/11 8:28 PM, Linus Flustillbe wrote:
> [...]
> So basically what I want to do is create a whole bunch of methods, put
> them in one class and have them all available on demand just by
> importing the class...no instantiations required.
> Make sense?   This is probably silly so if it is, just ignore me..I'll
> go away

Not silly at all.  If I understand your question correctly, you are 
asking about "static" methods (not to be confused with "static nested 
classes" :( ).  That is, a method that can be called using the type 
name, rather than an instance reference.

They can be quite useful, when you need to implement some functionality 
that does not depend on some specific instance data.

You can also have static data members; those members are, like the 
static methods, referenced using the type name rather than an instance 
reference.

See http://download.oracle.com/javase/tutorial/java/javaOO/classvars.html

Pete

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#9104

Peter Duniho wrote:
> On 10/22/11 8:28 PM, Linus Flustillbe wrote:
>> [...]
>> So basically what I want to do is create a whole bunch of methods, put
>> them in one class and have them all available on demand just by
>> importing the class...no instantiations required.
>> Make sense?   This is probably silly so if it is, just ignore me..I'll
>> go away
> 
> Not silly at all.  If I understand your question correctly, you are 
> asking about "static" methods (not to be confused with "static nested 
> classes" :( ).  That is, a method that can be called using the type 
> name, rather than an instance reference.
...

Also, see the class java.lang.Math for an easily accessible example of
this in practice.

Patricia

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#9102

On 10/22/2011 8:28 PM, Linus Flustillbe wrote:
> Does a method have to be part of a class that gets instatiated or can it
> live in a class to be available to all other classes without
> instantiation...it's available when it's imported?

> package helperClasses;
> public class rType {

         private rType() {}

  	public static  boolean isBetweenInt(int a, int b, int c)
> 	{
> 		return (a<= c&&  a>=b);
> 	}
  	public static boolean isBetweenDouble(double target, double lower, 
double upper)
> 	{
> 		return (target<= upper&&  target>= lower);		
> 	}
> }


   import static helperClasses.rType.*;
>
> class rTypeTest {
>    public static void main(String[] args) {

       boolean hello = isBetweenInt(4,6,87);
>     System.out.println(hello);  // weird choice of variable names...
>     }
> }

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#9103

Oh, and use method overloading, don't need to append "Int" and "Double" 
to your method names.

On 10/22/2011 10:12 PM, markspace wrote:

>> package helperClasses;
>> public class rType {
>
> private rType() {}
>
> public static boolean isBetween(int a, int b, int c)
>> {
>> return (a<= c&& a>=b);
>> }
> public static boolean isBetween(double target, double lower,
> double upper)
>> {
>> return (target<= upper&& target>= lower);
>> }
>> }
>
>
> import static helperClasses.rType.*;
>>
>> class rTypeTest {
>> public static void main(String[] args) {
>
> boolean hello = isBetween(4,6,87);
>> System.out.println(hello); // weird choice of variable names...
>> }
>> }
>

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#9113

On 2011-10-23, markspace <-@> wrote:
> Oh, and use method overloading, don't need to append "Int" and "Double" 
> to your method names.
>
> On 10/22/2011 10:12 PM, markspace wrote:
>
>>> package helperClasses;
>>> public class rType {
>>
>> private rType() {}
>>
>> public static boolean isBetween(int a, int b, int c)
>>> {
>>> return (a<= c&& a>=b);
>>> }
>> public static boolean isBetween(double target, double lower,
>> double upper)
>>> {
>>> return (target<= upper&& target>= lower);
>>> }
>>> }
>>
>>
>> import static helperClasses.rType.*;
>>>
>>> class rTypeTest {
>>> public static void main(String[] args) {
>>
>> boolean hello = isBetween(4,6,87);
>>> System.out.println(hello); // weird choice of variable names...
>>> }
>>> }
>>
>

So that works really well.

package helperClasses;

public class rType {
   public static boolean isBetween(int a, int b, int c)
   {
	return (a <= c && a >=b);
   }
   public static boolean isBetween(double target, double lower, double upper)
   {
	return (target <= upper && target >= lower);		
   }

}

import static helperClasses.rType.*;
class rTypeTest {
  public static void main(String[] args) {
     boolean hello = isBetween(4,6,87);
     System.out.println(hello);
     boolean hello2 = isBetween(5.4, 2.3, 9.2);
     System.out.println(hello2);
   }
}

 
false
true

I understand the concept of overloading methods... I haven't done much
Java in few years so I'm taking a refresher by going through the Java
Tutorial.  What does adding the "static" modifier to the import
statement do?  Since the methods in the rType class are already defined
as being static (only one instance no matter how many times the class is
instantiated ... see I read up on that)  why do we need the modifier 
except to make the code compile?  Or is that the only reason.. because
Java needs it? 

-- 
****************************************************************
* Usenet Impovement Project http://nacs.dyndns-office.com/usenet
****************************************************************

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#9115

On 10/23/2011 6:32 AM, Linus Flustillbe wrote:

> I understand the concept of overloading methods... I haven't done much
> Java in few years so I'm taking a refresher by going through the Java


More on overloading:
<http://download.oracle.com/javase/tutorial/java/javaOO/methods.html>


> Tutorial.  What does adding the "static" modifier to the import
> statement do?  Since the methods in the rType class are already defined
> as being static (only one instance no matter how many times the class is
> instantiated ... see I read up on that)  why do we need the modifier
> except to make the code compile?  Or is that the only reason.. because
> Java needs it?


By default "import" brings in class definitions, not the members of the 
class.  So

   import helperClasses.rType;

would import the class, and you'd have to use

   rType.isBetween( x, y, z);

C.f. that link Peter gave you, which uses this style of static method 
access.  "Import static" is a special import syntax that imports only 
the static members of rType, not the class definition, so that you can 
use its static methods and fields "bare," without a class name as a 
qualifier.  It's a convenience for typing (and reading), nothing else.

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#9120

Linus Flustillbe wrote:
> So that works really well.
> 
> package helperClasses;

By widespread but not quite universal convention, package names should be all lower case.

> public class rType {

By universal convention, class names should begin with an upper-case letter.
<http://www.oracle.com/technetwork/java/codeconv-138413.html>

>    public static boolean isBetween(int a, int b, int c)
>    {
> 	return (a <= c && a >=b);

PLEASE DO NOT INDENT USENET CODE POSTS WITH TABS!

>    }
>    public static boolean isBetween(double target, double lower, double upper)

Why did you switch to intelligent variable names here, but not in the other method?

>    {
> 	return (target <= upper && target >= lower);	

PLEASE DO NOT INDENT USENET CODE POSTS WITH TABS!
	
>    }
> 
> }
> 
> import static helperClasses.rType.*;
> class rTypeTest {

By universal convention, class names should start with an upper-case letter.

>   public static void main(String[] args) {
>      boolean hello = isBetween(4,6,87);
>      System.out.println(hello);
>      boolean hello2 = isBetween(5.4, 2.3, 9.2);
>      System.out.println(hello2);
>    }
> }
> 
>  
> false
> true
> 
> I understand the concept of overloading methods... I haven't done much
> Java in few years so I'm taking a refresher by going through the Java
> Tutorial.  What does adding the "static" modifier to the import
> statement do?  Since the methods in the rType class are already defined

Read the manual.
GIYF.
<http://lmgtfy.com/?q=Java+import+static>

> as being static (only one instance no matter how many times the class is
> instantiated ... see I read up on that)  why do we need the modifier 
> except to make the code compile?  Or is that the only reason.. because
> Java needs it? 

The "import static" directive lets you import static (get it?) members from another class.  This obviates having to prefix those members with the class and the dot operator.

-- 
Lew

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#9107

On 23 Oct 2011 03:28:31 GMT, Linus Flustillbe
<admin@nacs.dyndns-office.com> wrote, quoted or indirectly quoted
someone who said :

>Does a method have to be part of a class that gets instatiated or can it
>live in a class to be available to all other classes without
>instantiation...it's available when it's imported?

You can have static methods that can be called without creating any
objects.  The class itself will get loaded and an invisible class
object will be created with slots for all the static variables.

This is a very basic feature of Java.  I suggest you get an text, even
a badly out of date one, to explain such things.
see http://mindprod.com/jgloss/gettingstarted.html
-- 
Roedy Green Canadian Mind Products
http://mindprod.com
It should not be considered an error when the user starts something
already started or stops something already stopped. This applies
to browsers, services, editors... It is inexcusable to 
punish the user by requiring some elaborate sequence to atone,
e.g. open the task editor, find and kill some processes.

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#9114

On 2011-10-23, Roedy Green <see_website@mindprod.com.invalid> wrote:
> On 23 Oct 2011 03:28:31 GMT, Linus Flustillbe
><admin@nacs.dyndns-office.com> wrote, quoted or indirectly quoted
> someone who said :
>
>>Does a method have to be part of a class that gets instatiated or can it
>>live in a class to be available to all other classes without
>>instantiation...it's available when it's imported?
>
> You can have static methods that can be called without creating any
> objects.  The class itself will get loaded and an invisible class
> object will be created with slots for all the static variables.
>
> This is a very basic feature of Java.  I suggest you get an text, even
> a badly out of date one, to explain such things.
> see http://mindprod.com/jgloss/gettingstarted.html

Thanks Roedy.  I was just getting ahead of myself; thinking about "what
if" when I was still on the "what" topic.  As you can see from other
reponses to my question and my replies, I have figured it out for the
most part but still don't understand why I have to modify the import
statement... someone will probably say "that's just the way it has to
be" and if that's the case, that's fine.


-- 
****************************************************************
* Usenet Impovement Project http://nacs.dyndns-office.com/usenet
****************************************************************

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#9366

On 23 Oct 2011 13:49:19 GMT, Linus Flustillbe
<admin@nacs.dyndns-office.com> wrote, quoted or indirectly quoted
someone who said :

>
>Thanks Roedy.  I was just getting ahead of myself; thinking about "what
>if" when I was still on the "what" topic.  As you can see from other
>reponses to my question and my replies, I have figured it out for the
>most part but still don't understand why I have to modify the import
>statement... someone will probably say "that's just the way it has to
>be" and if that's the case, that's fine.

We were all newbies to start.  I have been figuring out Java, asking
endless questions and explaining this to newbies since the days of
Java 1.0.  I have been collecting explanations geared toward newbies
to programming and newbies to Java and posting them in the Java
glossary.  See http://mindprod.com/jgloss/jgloss.html

If you have trouble with something, often just reading one entry will
disabuse you of one of the common misconceptions that his throwing you
off.  Also chasing links at the bottom to related topics can be
fruitful.  Often the material you want is not filed where you expected
it.
-- 
Roedy Green Canadian Mind Products
http://mindprod.com
Capitalism has spurred the competition that makes CPUs faster and 
faster each year, but the focus on money makes software manufacturers 
do some peculiar things like deliberately leaving bugs and deficiencies
in the software so they can soak the customers for upgrades later.
Whether software is easy to use, or never loses data, when the company
has a near monopoly, is almost irrelevant to profits, and therefore 
ignored. The manufacturer focuses on cheap gimicks like dancing paper 
clips to dazzle naive first-time buyers. The needs of existing 
experienced users are almost irrelevant. I see software rental as the 
best remedy.

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#9109

On 2011-10-23, Linus Flustillbe <admin@nacs.dyndns-office.com> wrote:
<snipping my own stuff here>

Thanks all.. I just haven't gotten far enough into the tutorial yet I
guess since it seems what I am trying to do (static methods) is covered
later on.  If I had known what these things are called I might have been
able to discover this without posting.


-- 
****************************************************************
* Usenet Impovement Project http://nacs.dyndns-office.com/usenet
****************************************************************

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