Why does he do Object obj.

@Override
// we write the @Override because we implemented the Comparable interface
// if you implement an interface this interface has "empty" methods you need to define for usage
// interface is a contract, so we need to define the methods from that interface how they need to behave

public int compareTo(Object obj){

// this compareTo method thakes an object as argument (obj)
// in java everething is an objectr except primitive types like int, double and so on...
// so if you call compareTo method you NEED to give that methot an object
// so everething except primitives
// a Treet object for example

Treet other = (Treet) obj;
// in this part we convert our argument object  to Treet
// we gave the compareTo method an object of the Treet class, not a Treet
// we know that obj is a object of Treet but the compiler doesnt know it
// so we need to tell the compiler that obj is a Treet through this line of code above

If (equals(other))
// this is tricky here 
// other is our argument (object of the treet class ) that was converted into Treet 
// equals is comparing the Treet class itself with the Treet object we use as argument 
{
return 0;
// if the argument Treet is equal to the Treet class itself
// return 0
// it means that the Treets are equals to each other
}
int dateCmp = mCreationDate.compareTo(other.mDescription);
// if not equals
// we compare the Date and description of the Treets
if (dateCmp == 0)
{
return mDescription.compareTo(other.mDescription);
}
return dateCmp;
}