static field and final

Math fields for common mathematical constants

Declared in class Math with the modifiers public, final and static

public allows you to use these fields in your own classes.
A field declared with keyword final is constant—its value cannot change after the field is initialized.
PI and E are declared final because their values never change.
A field that represents an attribute is also known as an instance variable—each object (instance) of the class has a separate instance of the variable in memory.
Fields for which each object of a class does not have a separate instance of the field are declared static and are also known as class variables.
All objects of a class containing static fields share one copy of those fields.
Together the class variables (i.e., static variables) and instance variables represent the fields of a class.