As stated in the guide:

Default methods are backported by copying the default methods to a companion class (interface name + "$") as static methods, replacing the default methods in the interface with abstract methods, and by adding the necessary method implementations to all classes which implement that interface.

If I have this interface:

public interface TestI {
  default void test() {}
}

and this class:

public class TestC implements TestI {}

as far as I understand the output of retrolambda will be:

1. An interface with an abstract method test
2. A new class with a static method (empty in the example)
3. The class TestC with the implemented test method

So, If then I have a new class:

public class Test2 {
  static {
   new TestC().test();
  }
}

This should work. Am I right?

I'm asking this because it doesn't.

Test2.java:3: error: cannot find symbol
new TestC().test();
^
symbol: method test()
location: class TestC

If I decompile I found:

public abstract interface TestI {
  public abstract void test();
}
public class TestI$ {
  public static void test(TestI paramTestI) {}
}

and:

public class TestC  implements TestI {}

I don't think the last one is right. I'm doing something wrong or I didn't understand the section:

by adding the necessary method implementations to all classes which implement that interface.

If I use javap I obtain

public class TestC implements TestI {
  public TestC();
  public void test();
}

So the method is there but as the decompiler cannot find it neither javac does.

I tried both using compatibility with bytecode 50 and 51 using the latest version.

java -Dretrolambda.defaultMethods=true -Dretrolambda.bytecodeVersion=50 -Dretrolambda.inputDir=. -Dretrolambda.classpath=. -jar retrolambda.jar

You can reproduce it by using the same source code

Of course it would be nice if my TestC has all the implementation so that I can use it in other java7 project.