Why doesn't Java recognize my ArrayList in an overloaded constructor situation

Question

I have two constructors setup like so:

public XMessage(Information info, List<Object> results) {
    this.information = info;
    this.results = results;
}

public XMessage(Information info, Object result) {
    this(info, Collections.singletonList(result));
}

I create the XMessage object by passing in an Information object and an ArrayList object. When I inspect the result, it is a singleton list wrapping the ArrayList item. Why doesn't Java use the more appropriate constructor and what are my options to force it?

Answer 1

Calls first constructor:

new XMessage(information, new ArrayList<Object>());

Calls second constructor:

new XMessage(information, new ArrayList<String>());

ArrayList<String>() is not treated as List<Object> while ArrayList<Object> is. Consider using the following constructor:

public XMessage(Information info, List<? extends Object> results)

as @LuiggiMendoza suggested below.