Can someone help me to understand this paragraph from SCJP book
SCJP sun certified programmer for java 6 exam 310-065 book page 606 in the exam watch
"Remember that unboxing can't convert a plain old object to a primitive, even if that object reference refers to an integer(or some other wrapped primitive) on the heap.
unboxing converts onoly from a wrapper class reference (like an Integer or Long) to primitive."
I am quite confused about the concept between object reference refers to an integer on the heap vs unboxing converts onoly from a wrapper class reference (like an Integer or Long) to primitive., Can someone provide some examples to help me understand the difference between them.