Preconditions & postconditions
Rely on what is promised; never invent cases the spec does not state.
Preconditions state what the caller promises; postconditions state what the method guarantees. Reading them correctly is free points; writing code that ignores them is the classic time sink.
Precondition: scores.length >= 1
Postcondition: returns the highest score
What you may rely on: at least one element — so best = scores[0] is
safe, no empty check needed. What you must NOT add: a graceful empty
case. Code like if (scores.length == 0) return 0; is dead weight the
exam never asked for, and worse, it invents a contract (0 for empty)
the caller never agreed to.
Conversely, when the spec says "returns -1 if the value does not appear", the -1 IS the contract. A student who instead throws an exception or prints an error has rewritten the spec — automatic zero even if the rest is perfect.
The three questions to ask of every spec:
- What inputs are promised (preconditions)? → Skip guarding them.
- What outputs are guaranteed in every case (postconditions)? Enumerate the cases: normal, boundary, absent.
- What is explicitly out of scope? If it says "you may assume the array is sorted", do not sort it.