Which overload will get selected for null in Java?

java parameters methods invocation
Martijn Courteaux picture Martijn Courteaux · Oct 9, 2009 · Viewed 8.5k times · Source

If I write this line in Java:

JOptionPane.showInputDialog(null, "Write something");

Which method will be called?

  • showInputDialog(Component parent, Object message)
  • showInputDialog(Object message, Object initialSelectionValue)

I can test it. But in other cases similar to this, I want to know what happens.

Answer

Jon Skeet picture Jon Skeet · Oct 9, 2009

The most specific method will be called - in this case

showInputDialog(Component parent, Object message)

This generally comes under the "Determine Method Signature" step of overload resolution in the spec (15.12.2), and in particular "Choosing the Most Specific Method".

Without getting into the details (which you can read just as well in the spec as here), the introduction gives a good summary:

If more than one member method is both accessible and applicable to a method invocation, it is necessary to choose one to provide the descriptor for the run-time method dispatch. The Java programming language uses the rule that the most specific method is chosen.

The informal intuition is that one method is more specific than another if any invocation handled by the first method could be passed on to the other one without a compile-time type error.

Related questions

Does Java support default parameter values?

I came across some Java code that had the following structure: public MyParameterizedFunction(String param1, int param2) { this(param1, param2, false); } public MyParameterizedFunction(String param1, int param2, boolean param3) { //use all three parameters here } I know that in C++ I …

Read More
Python-like list comprehension in Java

Since Java doesn't allow passing methods as parameters, what trick do you use to implement Python like list comprehension in Java ? I have a list (ArrayList) of Strings. I need to transform each element by using a function so that …

Read More
When is a parameterized method call useful?

A Java method call may be parameterized like in the following code: class Test { <T> void test() { } public static void main(String[] args) { new Test().<Object>test(); // ^^^^^^^^ } } I found out this is possible from the Eclipse …

Read More