Overload resolution, which method is called

Question

Lets suppose I have a ComponentBase class, who is child of ObjectContextDecorator and grandchild of ObjectContext.

public class ComponentBase extends ObjectContextDecorator {
}

public class ObjectContextDecorator extends ObjectContext {

    public void set(String objectTypePath, String characteristicName, Object value) {
        //...
    }
}

public class ObjectContext {
    public void set(String characteristicName, Object value, boolean forced) {
       //...
    }
}

The set methods on ObjectContextDecorator and ObjectContext are very simillar. Consider this sample code:

ComponentBase base = new ComponentBase();
base.set(""OTM4E_EFFLEVEL"", ""IE1 / STD"", true);

Both methods' signatures fit the one being called correctly. I am not able to change the methods' signatures since it is not my code.

How does the compiler know which method I intended to call?

I know that on the IDE you can point out which method you are actually intending to call, but in this situation, I am using a class loader to load a class which has a method containing the sample code.

Answer 1

How does the compiler know which method I intended to call?

It checks for the arguments and determines which one is more specific following the rules described JLS §15.2

In your case, the call:

base.set("OTM4E_EFFLEVEL", "IE1 / STD", true)

the arguments are String,String, boolean

Which matches the first class (parameters names changed for brevity)

public class ObjectContext {
    public void set(String s, Object o, boolean b){
       //...
    }
}

The second class is not invoked because the third parameter is an Object:

public class ObjectContextDecorator extends ObjectContext {

    public void set(String s, String ss, Object thisOneRightHere) {
        //...
    }
}

and while the boolean value true can match if it is autoboxed still the first one is more specific. The rule that is applying here is:

The first phase (§15.12.2.2) performs overload resolution without permitting boxing or unboxing conversion

But, for instance, if you use the object wrapper Boolean in the signature:

public class ObjectContext {
    public void set(String s, Object o, Boolean b){ //<-- third param changed from boolean to Boolean
       //...
    }
}

Then they will both match, and the compiler would let you know with the following message:

> A.java:25: error: reference to set is ambiguous
>     base.set("OTM4E_EFFLEVEL", "IE1 / STD", true);
>         ^   both method set(String,Object,Boolean) in ObjectContext and method set(String,String,Object) in ObjectContextDecorator match

But that's not the case in your example.