HTTP put and POST methods

I read
HTTP put idempotent and does not change the state of object and suitable for updating given object.
Whereas and POST method is non idempotent which changes everytime state of object and not suitable for UPDATEs. I have not clearly understood the difference when to us UPDATE and PUT. please advise
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Think of them as database CRUD operations

POST = insert
PUT = update
DELETE = delete
GET = select
gudii9Author Commented:
POST is for ADD right?
i am bit confused about states of objects how they change and how they do not change due to ADD, UPDATE. please advise
mccarlIT Business Systems Analyst / Software DeveloperCommented:
Think of it this way...

If I "add" 10 items to an empty list, there are now 10 items in the list. Each of those 10 "add" operations changed the list in some way (they increased the size of the list by 1). So "add" is a non-idempotent operation.

If I do the same "update" to the first item in the list 10 times, the first update applies and then the next 9 are redundant as the change has already been applied. The first update changed the state of the object but the next 9 didn't really do anything. So "update" IS idempotent.
gudii9Author Commented:
what is literal meaning of idempotent and non-idempotent
it is bit confusing word.

idempotent means non changeable?
It means you can replay the operation without causing any side effects.

For example a GET request can be invoked multiple times and should not change the state.

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