Confusion with type casting and other things

It's been a while that I've watched these videos, so I'll answer your questions more generically. I'm sure someone else can provide you a more context specific answer. First you need to understand the concept of comparator in Java. So say you've a list of numbers, [2, 6, 7, 1, 3, 5], now you want to sort it. That's easy right, the answer list looks something like [1, 2, 3, 5, 6, 7]. So what was the sorting logic here - yes the natural order of real numbers. You could also have reverse sorted the numbers to something like - [7, 6, 5, 3, 2, 1] In both cases the natural order of numbers is used to sort. You can do the same with any primitive data types - int, float, char etc. However things get a bit hairy when you've to compare two objects. Say you have the following Student objects

class Student{ private name; private age; } Now if you need to sort a list of students, do you sort it by the first letter of the name, or the age. Well Java expects you to specify that. By specifying a comparator you're essentially specifying the order of two objects. Thus to specify that students objects should be compared based on their names you can write up something like this, public class NameComparator implements Comparator { @Override public int compare(Student o1, Student o2) { String name1 = o1.getName(); String name2 = o2.getName(); // ascending order (descending order would be: name2.compareTo(name1)) return name1.compareTo(name2); } } Now passing this comparator to a sort function will enable you to sort the students on the basis of their names. Hope this clarifies - 1 & 2 to some extent. If you wish more on the subject feel free to look up comparators on stack overflow. And yes every Java object inherits from the Object class. That's a language construct and you don't really need to understand the why, but well that's pretty much how it is.

Finally -3 `for (Treet exampleTreet : treets) { System.out.println(exampleTreet); }' treets is a collection to print all the items you need to iterate the for-loop.

System.out.println(treets); just prints the address of the collection object which in this case is an ArrayList and not the items contained in the collection. Hope this helps.

Every class in Java has a concept of this which is sometimes explicit and at other times implicit. This can often trip new programmers. In essence when you write. int dateCmp = mCreationDate.compareTo(other.mCreationDate); It actually means, int dateCmp = this.mCreationDate.compareTo(othet.mCreationDate); this here is the first object.

Thank you @Soumasish your answer helped me understand a bit more of this.

I'm still confused about how java passes objects into this statement without entering values into any parameters

   int dateCmp =  mCreationDate.compareTo(other.mCreationDate);

How does it know which is the first object and which is the second? what if there are more than 2 objects in the array of the object it's pulling from?

Ah ok so does that mean when there is an array of objects, this code will choose the first object (set as this.)and compare it to the other objects (set as other) from the array one by one until it reaches the last object in the array?

Thanks!

if (equals(other)) { return 0; } int dateCmp = mCreationDate.compareTo(other.mCreationDate); if (dateCmp ==0) { return mDescription.compareTo(other.mDescription); } return dateCmp; }

In the recursive when function call itself how come the -1 come from since it can only return i did not see any execution flow that indicate that there are possible to return as -1