Cannot understand the mechanism of/logic behind the compareTo()

1) The sort method is calling treet1.compareTo(treet2). Within compareTo we can access treet1 via this and treet2 obviously via treet2. So calling a method with one parameter is practically the same as calling a function in a procedural language with two parameters. this is an implicit first argument.

To elaborate on this here is an excerpt of the code Craig wrote:

public int compareTo(Object o) {
    Treet other = (Treet) o;
    // ...
    int dateCmp = mCreationDate.compareTo(other.mCreationDate);

To make this more explicit, we can add this when we access mCreation date of the current Treet. The this is not needed to be there.

public int compareTo(Object o) {
    Treet other = (Treet) o;
    // ...
    int dateCmp = this.mCreationDate.compareTo(other.mCreationDate);

Java expects a function with that signature (name, parameters etc.), but behind the scenes compareTo has an additional parameter and gets this as first argument. You can think of the function as follows (note the static). o1 is assigned the value for this.

public static  int compareTo(Object o1, Object o2) {
    Treet treet1 = (Treet) o1;
    Treet treet2 = (Treet) o2;
    // ...
    int dateCmp = treet1.mCreationDate.compareTo(treet2.mCreationDate);

2) You would normally do that, but it seems like Craig wanted to avoid using generics for now. You would need to implement the interface Comparable<Treet> for this to work.

Fantastic, I get it now. Thanks Lars!