What is Class.this in Java?

class Enclosing {
    void method(Enclosing other) {
        // ...
    }
    void otherMethod() {
        new Runnable() {
            public void run() {
                method(this); // Does not compile. 'this' is a Runnable!
                method(Enclosing.this); // Compiles fine.
            }
        }.run();
    }
}

class Enclosing {
    void method(Enclosing other) {
        System.out.println("Accessing method");
    }
    void otherMethod() {
        new Runnable() {
            public void run() {
                // method(this); // Does not compile. 'this' is a Runnable!
                method(Enclosing.this); // Compiles fine.
            }
        }.run();
    }
    public static void main( String args[] ) {
        Enclosing e = new Enclosing();
        e.otherMethod();
    }  
}