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Java provides three main ways to check type compatibility. Functionally, they are similar but are used in different contexts. Here they are, ordered by performance:
instanceof. This binary operator is the fastest and most commonly used. If you have an instance of
Class::isInstance. This method takes an object of type A as a parameter. It should be chosen when you have an instance of
Class::isAssignableFrom. This method takes
There is also a fourth method – attempting to cast an instance of type
instanceof. This binary operator is the fastest and most commonly used. If you have an instance of
A and can specify B explicitly, this is the preferred choice. If A (or more precisely, the type of the variable holding an instance of A) and B are not in the same inheritance chain, the instance cannot possibly be a subtype of B, and the compilation will fail with an inconvertible types error.Class::isInstance. This method takes an object of type A as a parameter. It should be chosen when you have an instance of
A available, but B is not known at compile time. For instance, if you have variables A a and Class bClass, you can check with bClass.isInstance(a).Class::isAssignableFrom. This method takes
Class<A>. It’s the only option left if you don't have an instance of A. You would use it as bClass.isAssignableFrom(aClass).There is also a fourth method – attempting to cast an instance of type
A to type B. If the types are incompatible, this cast will throw a ClassCastException. However, this is universally considered a poor practice, as building program logic on the basis of exceptions is not advisable. The reasoning behind this is detailed in Effective Java Item 57.No questions left to review in this channel
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