How does Java compiler resolve the ambiguity to decide which
转http://bobcat.webappcabaret.net/javachina/faq/01.htm#lan_Q120Q. How does Java compiler resolve the ambiguity to decide which methods to call?
A:
In the following example, four test() methods, if we pass ambiguous \b{null} to the test, which one should (will) be called? The 3 on top has super/subclass/sub-subclass relationship. The most specific one (down hierarchy) will be called. The 4th with String as a parameter, but it is a sibling of Tester. Ambiguity compile time error results.
package com.zsk.testnull;class Tester { void test(Object s) { System.out.println ("Object version"); } void test(Tester s) { System.out.println ("Tester version"); } void test(SubTester s) { System.out.println ("SubTester version"); } // Not compilable any more if you uncomment the line // since String and Tester are siblings// void test(String s) { System.out.println ("String version"); } public static void main (String args[]) { Tester c = new Tester (); // Ambiguous, the most specific one which fit will be call c.test (null); // SubTester version c.test (new Object()); // Object version } }class SubTester extends Tester{ }
"The informal intuition is that one method declaration 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." Quotation from JLS2
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