CODEWITHSUNDEEP
javavectorsubclass
Thunderforge
Thunderforge

Reputation: 20575

Trouble Using Vector's addAll( ) function when the Vector is in a containing class

Using Java 6 SE, I have a class that contains a Vector. There is a class method that simply calls the contained Vector's addAll() method with the same parameters for each. The Vectors can be of either type "Superclass" or type "Subclass" and I want the addAll() methods to support both. This whole setup might look like this:

public class VectorAContainer(){
    this.vectorA = new Vector<Superclass>();
}

public void addAll(Vector<Superclass> vector){
    this.vectorA.addAll(vector);
}

Then I want to call a line of code like this:

VectorAContainer container = new VectorAContainer();
container.addAll(vectorB); //where vectorB is a Vector<Subclass>

The problem is, Eclipse gives the following error:

"The method addAll(Vector<Superclass>) in the type VectorAContainer is not applicable for the arguments (Vector<Subclass>)."

Strangely, I have found that addAll() works if it's NOT inside of a class:

//No container with an addAll(), calling directly on vectorA
this.vectorA.addAll(vectorB); //No errors!

I don't see a difference between the two above cases. I would like to get the first way to work because I have a much more elaborate class that contains a Vector like the one above. I would greatly appreciate any help you all could provide!

Upvotes: 0

Views: 676

Answers (2)

Travis Meyers
Travis Meyers

Reputation: 23

It's because Superclass is a lower bound annotation meaning classes that are Super to Vector. If vectorB is a subclass to Vector then it won't work. AbstractList and AbstractCollection are Super to Vector. I believe you want to use. public void addAll(Vector<? extends Vector> vector){ vectorA.addAll(vector); }

P.S. Vector is an obsolete class. You should use ArrayList if you don't need a thread safe implementation.

*P.P.S. You don't need to use "this" unless you have two variables with the same name (e.g.

private Variable variableA;

public void example(Variable variableA){

this.variableA = variableA;

}

Upvotes: 0

SLaks
SLaks

Reputation: 887365

You need to accept a covariant generic parameter:

public void addAll(Collection<? extends Superclass> c)

You can see this in the declaration of addAll:

boolean addAll(Collection<? extends E> c)

Upvotes: 2

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