Step $1$: Inspect IntComparer.java and StringComparer.java

Java's built$-$in java.util.Comparator interface is a functional interface: an interface that has only one abstract method. Comparator's abstract method is named compare$()$ and takes two arguments for two items to compare. compare$($a$,$ b$)$ returns an integer:

greater than $0$ if a $>$ b$,$

less than $0$ if a $<$ b$,$ or

equal to $0$ if a $==$ b$.$

Comparator is a generic interface. The compare$()$ method's parameters are both type T$.$ Class IntComparer implements Comparator and so implements compare$()$ to compare two integers. Class StringComparer implements Comparator and so implements compare$()$ to compare two strings.