问了解java返回语句中的类强制转换异常

EN

public class testCastReturn{
    public test(){

       HashSet<String> StringHash; //a simple hash set

       HashMap(<String, ComplexObject> ObjectInfo; //the String value is the name of the complexObject, and complexObject has multiple members (in this instance it is a java model for a database field so it has info pertaining to Key, size etc)

       //create a ComplexObject here
       addToObjectInfo(aComplexObject); // add it into the HashMap

       //repeat above a number of times....
       //now collect the 'names' of those objects
       StringHash = getObjectKeys();
    }

    public void addToObjectInfo(complexObject c){
        //put a complex object into the HashMap

        ObjectInfo.put(c.getNameID, c); //create a set of key value pairs where the name of the object is the key to get the actual object
    }

    public HashSet<String> getObjectKeys(){
       //retrieve the keys only
       return HashSet<String> this.ObjectInfo.keySet(); //fails with classCastException
       //this however works
       HashSet<String> temp = new HashSet<String>(this.ObjectInfo.keySet());
       return temp;   
    }  
 }//end class