Kept promise, while being an example in Java, say (8,4)

I believe the answer is:

reserved word

'an example in java say' is the definition.
(computing term - Java is a computer language)

'kept promise' is the wordplay.
'kept' becomes 'reserved' (reserving is a kind of keeping).
'promise' becomes 'word' (as in 'I give you my word').
'reserved'+'word'='RESERVED WORD'

'while being' acts as a link.

I've seen this clue in The Times.

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