Which of the following signatures declares a constructor for a Ship object in Java?

The reason this choice is correct is that in Java, a constructor must have the same name as the class it constructs—in this case, the class name is "Ship." Additionally, constructors do not have a return type, not even "void."

The presence of the access modifier "public" before the constructor allows the constructor to be accessible from other classes, which is vital for the object's creation in a broader context. So, the signature "public Ship()" correctly defines a public constructor for the Ship class.

The other options have characteristics that disqualify them from being valid constructors. The first option, "Ship()", lacks an access modifier, meaning it's package-private by default, which is not necessarily incorrect but does not provide the same level of accessibility to the constructor. The third option, "Ship public()", incorrectly places the access modifier after the class name, which is not syntactically valid in Java. Lastly, "public void Ship()" wrongly includes "void," which indicates a method, not a constructor, and hence does not meet the criteria for constructor declarations.