Difference between a Variable and a Field?

[Div Raj]

Hi,

I read in a book that, Instance variables are Non-static fields.
And Class variables are Static fields.
Also Parameters are classified as variables and not fields.

Could any one tell me what's the difference between a Variable and a Field?



Thanks
---------

[Campbell Ritchie]

A field is valid (in scope) throughout the whole class/object. A field is in fact a kind of variable, but it applies to the whole class/object.

[Div Raj]

ThankYou Ritchie

But I've one doubt; the Class variable/Instance variable is also having their scope throughout the class/object. Right?


Thanks
--------

[Campbell Ritchie]

A class variable is what you call a static field. That has scope throughout the whole class, and is accessible from any method of that class, static or instance (non-static).
An instance field is not accessible from any static parts of the class.

[Div Raj]

ok.
So could you please tell me what is a Field?

Thanks
-----------

[Campbell Ritchie]

Any variable declared outside methods, initialisers, etc. If you declare a variable inside the class and not inside a method, initialiser, etc, then it is called a field

public class Kettle
{
   private int temperature;
 
   public void becomeHotter(int degrees)
   {
      int heat = temperature + degrees;
      temperature = heat;
   }
 
   public int getTemperature()
   {
      return temperature;
   }
. . .
}

The variable temperature is declared inside the class and outside the methods; you call it a field. It is accessible and in scope in the two methods shown.
The "variable" degrees is "declared" inside the () for the becomeHotter() method; it is a parameter, and is not a field. Its scope is that method.
The variable heat is declared inside the becomeHotter method. It is a local variable and its scope is from "int heat . . ." to the end of the method. It is not a field.

Does that help?

[Div Raj]

ok. Now I got it.

ThankYou Ritchie

[Campbell Ritchie]

You're welcome