Question

How to declare a headset using double as datatype?

public HashSet priceSet() {
    Set<double> hSet = new HashSet<double>();  //<==== netbeans warn this line
    for (Map.Entry<String, Tablet> entry : tableMap.entrySet()) {     
        hSet.add(entry.getValue());
    }        

    return (HashSet) hSet;
}

what’s the problems of this line?
Set hSet = new HashSet();

Answer 1

Set is used for storing objects, not primitives. So you should use wrappers to use it with primitives – like

Set<Double> hSet = new HashSet<Double>();

edit
provided you have some double variable, you add it like

double test = 0.0;
hSet.add((Double)test);

however entry.getValue() is Tablet, so it seems you need to use something like

hSet.add((Double)entry.getValue().getValue());

edit2 actually (Double) isn’t necessary