singleton in php?

i want it so i only ever have one object of this class ever in my program.
all new instances of the object will simple be references to the first
object.

how can i implement this? i can do it in java by making the constructor
private and then having a static method to return a static variable init to
an object of the class if it is not init yet.

how can i have a singleton object in php?
ASAP via email as well. cheers