Classes and objects in Java - JavaTech: An Introduction to Scientific and Technical Computing with Java - page 69

seen examples of static methods in the Math class. In fact, Math is a class of
nothing but static member variables and static methods. The Math class itself
cannot even be instantiated. The only way to access the various constants and static
methods in the Math class is with the Math.constant and Math.method()
syntax.
If a class property is also declared final , then it becomes a constant value
that cannot be altered. In the following example, the static data field PI is now a
fixed constant. By convention, constants are normally written with all uppercase
letters.
class ConstHolder {
public final static double PI = 3.14;
}
3.6 More about primitive and reference variables
Primitive data type operations deal only with value. For example, the following
code shows that assigning primitive data variable i to another primitive named j
simply passes a copy of the value in i into j . That is, a datum's value is passed,
not a reference or pointer to a data location.
int i = 1; // Variable i holds the value 1.
int j = i; // Now j holds 1 also, that is, i's value is
// copied to j
i = 2; // Now i is 2, but j still holds the value 1
Similarly, in method parameters, primitive variables are passed by value. That is,
a copy is made and passed to the method. Changes to the passed value inside the
method cannot affect the value in the calling code.
The following snippet creates an instance of AClass and then invokes the
change() method with an int parameter.
... a method in some class ...
int i = 2;
AClass a1 = new AClass ();
a1.change (i);
int m = i; // m = 2, no matter what happens inside
// a1.change()
System.out.println ("i ="+ i);
...