Classes and objects in Java - JavaTech: An Introduction to Scientific and Technical Computing with Java - page 68

Static values are declared with the static keyword. For example, in this
class the variable pi is declared static :
public class ConstHolder
{
public static double pi = 3.14;
}
When the JVM loads the byte code for the class description of ConstHolder ,
it creates a single memory location for the pi variable and loads it with the
value 3.14. All instances of the ConstHolder class can access the exact same
value of pi . The pi data exists and we can access it even when no instance of
ConstHolder is created. Since pi is a member variable of the class, though
a special one because it is static, it can be accessed just like any other member
variable. For example, if g1 is an instance of Test , then we can access the
variable pi as follows:
ConstHolder c = new ConstHolder();
double twopi = 2.0 * c.pi;
If there is no instance of ConstHolder ,wecan access the data directly using
the name of the class:
double twopi = 2.0 * ConstHolder.pi;
In practice, it is a good habit to always use the latter syntax, even when a class
instance exists, since it makes clear to the reader that the referenced variable is a
static member variable of the Test class.
In addition to static member variables, we can also define static methods,
producing methods that can be called without instantiating the class. For example,
public class ConstHolder {
public static double pi = 3.14;
public static double getPI () {
return pi;
}
}
We could, in this case, use the getPI() method to obtain the value of pi :
double x = 2.0 * ConstHolder.getPI ();
A static variable or method is also called a class variable or method, since it
belongs to the class itself rather than to an instance of that class. We've already