Instance Variables

[Stephen Foy]

How do you create them in java?

[Ko Wey]

Read the stuff on this page:
http://java.sun.com/docs/books/tutorial/java/javaOO/classvars.html

[marc weber]

Whenever you declare a variable without the keyword "static," you have an instance variable.

This is all explained in Ko's link above, but let me try my own brief explanation...

You define Java classes, which (usually) include fields (variables) and methods (functions).

The class can serve as a "blueprint" for creating an object, also known as an "instance" of the class (which you create using the keyword "new"). By default, fields and methods are "instance" members, meaning that an instance must be created in order for these fields and methods to be used.

In contrast, fields and methods can be declared "static," in which case they are not associated with any particular instance, but are instead simply associated with the class itself. To use static fields and methods, no instance needs to be created -- they can be called directly from the class.

class MyClass {
  int instanceInt = 7;
  static classInt = 5;
}
 
class Demo {
  public static void main(String[] args) {
    System.out.println(MyClass.classInt); //call from class
    MyClass myInstance = new MyClass(); //create instance
    System.out.println(myInstance.instanceInt); //call from instance
  }
}

[ November 12, 2005: Message edited by: marc weber ]

[armeen golden]

so can we say that instance varialbes are associated with a particular instance and not with the entire class?

[Paul Clapham]

Yes, that is correct.