Java Glossary : dynamic typing

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dynamic typing

Java is a statically typed language. In a dynamically typed language, typically:

Variables do not have type constraints on them. They are generic and can point to anything.
The identity of method calls, a.k.a. messages can be computed and manipulated at run-time, and then an object (reference) plus this message value combined to make a call. Matt Kennel would call this dynamic messaging.
Note, this is not polymorphism in the standard OO sense. There, the identity of the specific subroutine is computed at runtime with a combination of the run-time-varying specific type, plus the statically known method call name.
Imagine this: in a dynamically typed language, you could pop off three stacks: object reference, message reference, arguments, mix them, and call the result.
Occasionally (in some research languages) dynamic typing means the identity of 'which type is some object' is computed as a user-defined predicate upon its run-time varying data, and is not an invariant of its creation. The object's type may mutate, perhaps as it acquires additional fields.

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