uses interface as type

[j2me64]

I'm just reading "Effective Java" from J. Bloch and I full agree with "uses interface as type". But, exactly with the example shown

// Good - uses interface as type
List subscribers = new Vector();

some useful methods inside the class Vector (ex. firstElement(), insertElementAt()) will not be visible in subscribers. Ok, subscribers could be casted to Vector, to access the method firstElement(). But, in the case you need methods of Vector is "use interface as type" still a good programming recommendation?

[JosAH]

I'm just reading "Effective Java" from J. Bloch and I full agree with "uses interface as type". But, exactly with the example shown

// Good - uses interface as type
List subscribers = new Vector();

some useful methods inside the class Vector (ex. firstElement(), insertElementAt()) will not be visible in subscribers. Ok, subscribers could be casted to Vector, to access the method firstElement(). But, in the case you need methods of Vector is "use interface as type" still a good programming recommendation?

Yes it is; as long as you only use the type (here: List) you're free to change the implementation (here: Vector) for another implementation, e.g. ArrayList. If you use the implementation type/class (here: Vector) your code is tied to the implementing type/class. As a corollary rule of thumb: use the least specific type that is still of use, so using a Vector as a type Serializable is too general and it is of (almost) no use.

kind regards,

Jos

[Tolls]

(S)ome useful methods inside the class Vector (ex. firstElement(), insertElementAt()) will not be visible in subscribers. Ok, subscribers could be casted to Vector, to access the method firstElement(). But, in the case you need methods of Vector is "use interface as type" still a good programming recommendation?

As a corollary rule of thumb: use the least specific type that is still of use, so using a Vector as a type Serializable is too general and it is of (almost) no use.

kind regards,

Jos

The higlighted bit answers that question. If you need the methods in Vector then clearly List is too general a type to be using.