用ant编译错误

Question

I'd really tough time understanding what went wrong. Beginning with this, I've an interface like this...

public interface UserRecordsInterface  
{  

    public abstract List getRecordsVector()  
        throws UserExitException;  

}  

I wanted to implement this interface in my class MyRecordsClass.java like this...

public class MyRecordsClass implements UserRecordsInterface{  

    private List addendaRecs             = null;  

     /** 
     * Return the list of addenda records 
     *  
     * @return List 
     */  

    public List getRecordsVector() {  
        return addendaRecs;  
    }  
}  

While compiling using ant, I got 2 errors..

1 Class MyRecordsClass is not abstract and does not override the abstract method getRecordsVector() in UserRecordInterface.

2 getRecordsVector() in MyRecordsClass cannot implement getRecordsVector() in UserRecordsInterface; attempting to use incompatible return type. getRecordsVector() in MyRecordsClass cannot implement getRecordsVector() in UserRecordsInterface; attempting to use incompatible return type.

 - [javac] found : java.util.List 
 - [javac] required: java.util.Vector 
 - [javac] public List getRecordsVector() {

Initially, the method getRecordsVector() had return type Vector in the interface. Now, it was changed to List. So, I've changed accordingly in my class. Now, its giving this error. If I change my class to Vector & compile, then its working fine. But I want to use List, because thats what currently the interface has. So, I believe that ant is still pointed to the old lib that has vector interface. Not sure, if this is some problem with ant or with my code. Please suggest..

Answer 1

You don't need the abstract modifier in an interface, and I have a hunch that is what is causing your problems. The only place to use abstract methods is in abstract classes.

EDIT

I think it's likely that the interface has recently changed and in a separate jar.

It probably used to return a Vector, but now the source you see returns a List.

I suspect you are compiling with an old version of the jar (one in which getRecordsVector() still returns a Vector ) in your classpath.

Answer 2

What version of Java are you using? I am running Java7 inside IntelliJ IDEA and it didn't complain about the code - it actually compiled and I can run if I put a main method in there.

I agree with @NickJ's comment - interface methods are by nature abstract - because you must implement them in the class that implements the interface. See this posting for more information.