In what context are statements in Java interface definitions executed?

I'm looking at the definition of org.apache.maven.plugin.Mojo:

public interface Mojo
{
    String ROLE = Mojo.class.getName();
    [...]
}

I'm lost. To my knowledge, Java interfaces are a set of method signatures. So what's this line which looks like a statement doing here? What are the semantics? For example:

When does that line get "executed"?
In the context in which that line runs, what does Mojo refer to? What is its type?
In the context in which that line runs, what does Mojo.class refer to? I assume its type is java.lang.Class?
In what context can I read that ROLE variable? What is the syntax for doing so? What will the variable contain?
Can I write to that ROLE variable?

Solution

All the fields of an interface are implicitely public, static and final. So this is the same as writing

public static final String ROLE = Mojo.class.getName();

It defines a constant, that all the users of the interface can use, as any other constant: Mojo.ROLE. This line is executed when the Mojo interface is initialized by the ClassLoader. Mojo.class is the Mojo class, indeed of type java.lang.Class<Mojo>. Since the package of the class is org.apache.maven.plugin, the value of the constant will be "org.apache.maven.plugin.Mojo".

Look here for the relevant section of the Java language specification.