08: Writing Comparators

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In class, we had PostalAddress implement the Comparable interface and wrote a compareTo method to give it a natural order. Sometimes we want to define additional orderings on a class, and so we define a new Comparator class for each such ordering. (See the notes for an examples of using a “postal sort”).

(2 points) Define a Comparator for Strings such that a sort call on a List<String> of strings sorts the strings by length, shortest to longest. Show the entire class definition.

Hints:

• Start with the class declaration; it should be of type Comparator with an appropriate type parameter.
• You only have to implement one method.
• Use a method of String to get its length.
• You can compare the lengths using <, >, and == correctly, or you can use Integer.compare (examples of each are shown in the notes).