Re: JDK 1.5 Compiler not enforcing parameterized type in interface?

From:

Thomas Hawtin <usenet@tackline.plus.com>

Newsgroups:

comp.lang.java.programmer

Date:

Thu, 24 Aug 2006 19:41:39 +0100

Message-ID:

<44edf2e8$0$3223$ed2619ec@ptn-nntp-reader01.plus.net>

googlegroups-nospam4me@sneakemail.com wrote:

public interface MyInterface {
    public void doSomething(Collection<Integer> collection);
}

Why doesn't it complain if it is excluded from the implementing class?

public class MyClass implements MyInterface {
    public void doSomething(Collection collection) {
    collection.add(new String());
    }
}

I would expect one of 2 compiler errors:
1. MyClass doesn't implement the interface correctly since the method
signatures are different.

As far as the JVM is concerned, both are methods called doSomething that
take a single Collection argument and return void. The signature is the
same.

The advantage of erasure is that if the base class had been updated to
use generics, the old derived class still works.

2. String can't be added to collection of Integer.

The static type is Collection, not Collection<Integer>.

When you compile the code, you should get a warning. Listen to compiler
warnings.

Tom Hawtin
--
Unemployed English Java programmer
http://jroller.com/page/tackline/