Which constructor is chosen when passing null?

In the following example, I have 2 constructors: one that takes a String and one that takes a custom object. On this custom object a method "getId()" exists which returns a String.

public class ConstructorTest {
 private String property;

 public ConstructorTest(AnObj开发者_JS百科ect property) {
  this.property = property.getId();
 }

 public ConstructorTest(String property) {
  this.property = property;
 }

 public String getQueryString() {
  return "IN_FOLDER('" + property + "')";
 }
}

If I pass null to the constructor, which constructor is chosen and why? In my test the String constructor is chosen, but I do not know if this will always be the case and why.

I hope that someone can provide me some insight on this.

Thanks in advance.

By doing this:

ConstructorTest test = new ConstructorTest(null);

The compiler will complain stating:

The constructor ConstructorTest(AnObject) is ambiguous.

The JVM cannot choose which constructor to invoke as it cannot identify the type that matches the constructor (See: 15.12.2.5 Choosing the Most Specific Method).

You can call specific constructor by typecasting the parameter, like:

ConstructorTest test = new ConstructorTest((String)null);

or

ConstructorTest test = new ConstructorTest((AnObject)null);

Update: Thanks to @OneWorld, the relevant link (up to date at the time of writing) can be accessed here.

The compiler will generate error.

Java uses the most specific contructor it can find according to arguments.
PS: if you add constructor (InputStream) , compiler will throw error because of ambiguety - it cannot know what is more specific: String or InputStream, because they are in different class hierarchy.