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Because
hipo null is an instance of Object. What you are doing is concatenating the
String "hipo" to the Hippo reference with the + operator and then seeing whether the whole thing is an instance of Object.
Remember the rules are: always go left‑to‑right. Higher precedence operators on the right, or right‑associative operators, are then taken into consideration.
Remember also that + has a higher precedence than
instanceof, so you are still going left‑to‑right.