Do you mean it's the only one without static types? All three are dynamically typed to some degree. For example, in ObjC, messages dispatch on the dynamic type of the object.
Both Objective-C and Java are statically and strongly typed. What you're thinking about is probably a runtime-reflection mechanism. The JVM, java's host is capable of supporting dynamic languages through 'invokevirtual' but it doesn't make java dynamically typed.