Ben’s Lecture Cliff Notes
Generic Functions
• I want to write generic functions, so I don’t
have to rewrite them again.
• The problem is functions often depend on
functionality provided by the parameters.
• How can I write a generic function, using
generic parameters, yet those parameters are
mandated to have certain functionality?
– Answer: Interfaces (a contract of functionality)
• Required methods, but the definition is up to the user.
A Generic Sort
• To write a generic sort, I need to be able to
compare the objects I am asked to sort.
• Each object must have a function to compare
itself with another object.
– Solution: The sort function accepts a collection of
objects that implement the Comparable interface
• Comparable objects have a compareTo function.
• Now I can sort any collection so long as the
objects implement this interface, using one sort
function.
– Call compareTo for each object in the collection.
Problem
• The Comparable interface only provides one
way to compare.
• What if I need diverse mechanisms of
comparison? (sort by size, shape, color, ….)
• How do I write a generic sort algorithm that
can sort the objects by comparing any
characteristic?
– Answer: Provide the sort a Comparator in addition
to the collection
Comparator
• The Comparator interface contains one
method, compare.
• The sort function can then use any object that
implements the Comparator interface to
perform the comparisons desired, and then
the sort can sort accordingly.
• Sort accepts the collection and the
comparator.