I know that the Java Comparable interface has only one method, which has an int return type. However, I'm not sure what I am actually doing when I want to override the compareTo method. It's important to me to understand programming and not just memorizing it. For example, in the following ... More on stackoverflow.com

The Java String compareTo() method is used for comparing two strings lexicographically. Each character of both the strings is converted into a Unicode value for comparison. If both the strings are equal then this method returns 0 else it returns positive or negative value. The result is positive if the first string is lexicographically greater than the second string else the result would be negative. More on reddit.com

A few thoughts: compareTo does not return -1, 0, 1. compareTo only guarantees that it returns either a negative, zero, or positive number. It would be incorrect to write code that compares the output of a call to compareTo against -1 or 1. e.g. if (a.compareTo(b) == -1) // wrong if (a.compareTo(b) < 0) // right CompareTo is used to establish the idea that one object can be greater than, equal to, or less than another object. For instance, Integers are Comparable, and they have a compareTo method. One Integer is larger than another if the int value it contains is larger (numerically) than the other. Strings are Comparable. Doubles are Comparable. As you noted, many other things can be Comparable, such as Students. Java chose to compare Strings lexicographically. This is similar to how a real-life dictionary would sort words in the English alphabet. Essentially, Strings are sorted the same way they would be sorted in the dictionary, and we use the ASCII table as the alphabet (instead of a regular 26-letter alphabet). This implies that capital letters come before lower-case letters. (e.g. "Z" < "a") The ternary operator is ? :. The syntax is: b ? x : y Where b is a boolean expression. x and y are expressions. If b is true, then the ternary operator returns x. Otherwise, it returns y. For instance, rather than writing: int x = 3; // or whatever other value you want if (x < 5) System.out.println("x is less than 5"); else System.out.println("x is greater than or equal to 5"); You can instead write: int x = 3; // or whatever other value you want System.out.println(x < 5 ? "x is less than 5" : "x is greater than or equal to 5"); More on reddit.com

public class Sorter> { ... public int compareTo(T other) { if(this.compareTo(other) > 0) return 1; else if(this.compareTo(other) == 0) return 0; else return -1; } } I'm not sure I understand what you're trying to do with your compareTo() method. You're attempting to compare a Sorter object with a T object? That is not a logical comparison. I'm not sure why you even need this method. In your sortIds(List, List) method, you're correctly using the compareTo() method of the Comparable objects. === Also in lines 17-19, do I need to have the cast there, or is there another way around it? The casts that you're performing in your constructor are not safe. There is no way of knowing that the object at temp[0] is actually of type T. For example, if you created a new Sorter(scanner), the code in your constructor would obviously not be correct, since temp is an array of Strings, and you'd be casting them to Integer. It the constructor may run without error, due to the type-erasured nature of generics, but you'll eventually run into problems when you think you have a List, but it is actually List, for example. I don't even think that code should be part of the constructor. You should read the input in a separate method, (such as your main() method), where you can convert the input to the appropriate Comparable types (e.g. parsing an integer from the String input), and then pass your type-safe IDs to your Sorter class. More on reddit.com