JDK-8091393: Observable collections for ObservableMap views

[Tom Schindl]

Hi,

Well the binary compat IMHO is not a problem. If your subtype overwrites 
the return type of a method the compiler will inserts a bridge method:

Take this example

package bla;

import java.util.ArrayList;
import java.util.Collection;
import java.util.List;

public class Test {
	public interface IB {
		public Collection<String> get();
	}
	
	public interface I extends IB {
		public List<String> get();
	}
	
	public class C implements I {
		public ArrayList<String> get() {
			return new ArrayList<String>();
		}
	}
}

if you look at C with javap you'll notice

Compiled from "Test.java"
public class bla.Test$C implements bla.Test$I {
   final bla.Test this$0;
   public bla.Test$C(bla.Test);
   public java.util.ArrayList<java.lang.String> get();
   public java.util.Collection get();
   public java.util.List get();
}


The problem is more that if someone directly implemented ObservableMap 
him/her self that it won't compile anymore. So it is a source 
incompatible change.

Tom

Am 30.05.22 um 08:58 schrieb John Hendrikx:
> It's not binary compatible, as changing the return type results in a new 
> method that compiled code won't be able to find.
> 
> See also "change result type (including void)" here: 
> https://wiki.eclipse.org/Evolving_Java-based_APIs_2#Evolving_API_interfaces_-_API_methods 
> 
> 
> --John
> 
> On 30/05/2022 03:22, Nir Lisker wrote:
>> Hi,
>>
>> Picking up an old issue, JDK-8091393 [1], I went ahead and looked at the
>> work needed to implement it.
>>
>> keySet() and entrySet() can both be made to return ObservableSet rather
>> easily. values() will probably require an ObservableCollection<E> type.
>>
>> Before discussing these details, my question is: is it backwards 
>> compatible
>> to require that these  methods now return a more refined type? I think 
>> that
>> it will break implementations of ObservableMap out in the wild if it
>> overrides these methods in Map. What is the assessment here?
>>
>> https://bugs.openjdk.java.net/browse/JDK-8091393