Problem of the Day  At low tide, a ship docks in the harbor  Ship is 9’ above the water line when it docks  Over the side hangs a rope ladder w/ rungs 1’ apart  Tide rises at a rate of 9” per hour After 6 hours what length of ladder will still be above water?

Problem of the Day  At low tide, a ship docks in the harbor  Ship is 9’ above the water line when it docks  Over the side hangs a rope ladder w/ rungs 1’ apart  Tide rises at a rate of 9” per hour After 6 hours what length of ladder will still be above water? 9’ – the ladder will rise with the boat!

CSC 212 – Data Structures

Problem With Position  Really, really limited in how it can be used  Provides way of holding & accessing an element  No way to use element with a Position  Great for keeping unorganized lists of information  Sucks for anything else like: Keeping a list whose data is automatically sorted Searching for something within huge collection Use data for analysis by linking related items Prioritizing items to stay up-to-date on demands

How Much Info Can You Get?

How Do We Organize Data?

Key Key To How We Organize Data

Entry To The Rescue  Entry provides 2 items to view & use data valu(e)  Preserves keeping the valu(e)able data we care about  Key  Key detail used to organize valuables also maintained

Entry To The Rescue  Entry provides 2 items to view & use data valu(e)  Preserves keeping the valu(e)able data we care about  Key  Key detail used to organize valuables also maintained interface Entry { K key(); V value(); }

KeyValue What’s The Key & Value?

Comparable Interface  Provides simple, abstract way to compare data  Found in java.lang package just like Iterable  Makes coding easier by simplifying search & compare  Total ordering relation needed to implement exactly one  Must be exactly one of a b  If a < b & b < c then a < c implied by this definition

Comparable Interface  Single method defined by Comparable int compareTo(E o)  Compare this instance with o (ther) instance  The only thing that matters is relative value returned  Specific value meaningless & only defines result is: negative zero positive negative if this o

Comparable Example positive 0 negative class Student implements Comparable { private float qpa;... public int compareTo(Student other) { if (qpa > other.qpa) { // Need to return positive number here return 73; } else if (qpa == other.qpa) { // Need to return 0 in this case return 0; } else { // Need to return negative number here return ; } }

Using Comparable Student match(float grade, Iterable it){ Student seeker = new Student(); seeker.setQPA(grade); for (Student s : it) { if (seeker.compareTo(s) == 0) { return s; } } // Prof. Idiot forgot to define Exception for this unexpected event, so… return null; }

What Does compareTo() Match?

And Your Reaction Should Be…

 NHL team class can only have 1 compareTo  But many ways to compare and rank teams

And Your Reaction Should Be…  NHL team class can only have 1 compareTo  But many ways to compare and rank teams  Is writing specific case-by-case code our fate?

Comparator to the Rescue!  Can also use Comparator s to compare data  Interface in java.util package (like Iterator )  Like Iterator, is separate class performing work  Comparator defines single method int compare(E o1, E o2)  Specific value meaningless; result defined by: negative zero positive negative if o1 o2

positive 0 negative class WinComp implements Comparator public int compare(NHLTeam o1, NHLTeam o2) { if (o1.getWins() > o2.getWins()) { return 42; // Need to return positive number here } else if (o1.getWins() == o2.getWins()) { return 0; // Need to return 0 in this case } else { return -68; // Need to return negative number here } } class PointsComp implements Comparator public int compare(NHLTeam o1, NHLTeam o2) { return (o1.getPoints() - o2.getPoints()); } } Comparator Example

Using Comparator int rank(NHLTeam team, Comparator comp, Iterable it){ int count = 1; for (NHLTeam goons : it) { if (comp.compare(team, goons) < 0) { count++; } } // Rank of the given team for this metric return count; }

Your Turn  Get into your groups and complete activity

For Next Lecture  Read GT – for Friday's lecture  What is a PriorityQueue and what does it do?  Queue sounds familiar; is there any relationship?  How can I link Marx, Orwell, & Homer Simpson?  Week #14 assignment posted & due Tuesday  Programming Assignment #3  Programming Assignment #3 due next Friday