[HD-OCP17/21-Fundamentals Pg 247, Sec. 10.2.1 - using-multiple-pattern-variables]
Posted: Wed Jan 01, 2025 7:20 am
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Number n = null;
//using instanceof for type comparison
if(n instanceof Number){ //valid for all versions, false if n is null
}
if(n instanceof Object){ //valid for all versions, false if n is null
}
//using instanceof for pattern matching
if(n instanceof Number num){ //compilation error in Java 17 but not in Java 21
}
if(n instanceof Object num){ //compilation error in Java 17 but not in Java 21
}This is incorrect because the following will not give compilation error in Java 17
if(n instanceof Number num){ //compilation error in Java 17 but not in Java 21}
and honestly it would be more simplier to just say "In Java 17, you cannot use pattern matching with a supertype" period