Lectures (CS 2110 Fall 2023)

Lecture 25: Priority queues and heaps

Required reading

Chapter 7: 7.19–7.21
Chapter 8: 8.34
Chapter 24: 24.32–24.34
Chapter 27

Instructor’s notes

The textbook places the root of the tree at array index 1 instead of 0, which simplifies the parent/children formulas a bit. But it later reimplements reheap() (analogous to our bubbleDown()) using a 0-based convention for use in heapsort. We’ll stick to the 0-based convention.

The textbook makes a point of avoiding swaps when bubbling up and down by only moving existing values and not writing the new value until its final location is known. This is a legitimate optimization, but we’ll stick with swaps because they make it easier to visualize the comparisons that are taking place.

At this point in the textbook, its method specifications range from poor to missing altogether. We’ll try to do better in our demo code.

Supplemental reading

JavaHyperText: Heaps, HeapSort
Myers: Priority Queues and Heaps

Lecture 24: Shortest paths

Required reading

The shortest-path algorithm
Chapter 29: 29.16–29.24
Chapter 30: 30.24

Instructor’s notes

The online reading (including videos) from JavaHyperText is much more thorough than the textbook on this topic, highlighting the loop invariant and proof of correctness.

Supplemental reading

Myers: Dijkstra’s single-source shortest path algorithm

Lecture 23: Graph traversals

Required reading

Chapter 29: 29.11–29.15
Chapter 30: 30.23

Instructor’s notes

DFS is most cleanly implemented recursively (as in lecture), which is not shown in the textbook. The textbook’s iterative implementation does a better job of matching a recursive version than others I’ve seen (e.g. JavaHyperText), but the pseudocode leaves out some details, and there is no concrete implementation in chapter 30.

The textbook’s treatment of topological sorting describes Kahn’s algorithm, but in reverse, starting with the last vertex in the order and accumulating vertices in a Stack to effectively reverse the order that they were added in. It also only provides pseudocode, leaving out details for how to efficiently find nodes with no successors after vertices have been removed. The lecture slides and demo code show the “forward” Kahn’s algorithm, including an efficient way of identifying nodes with no predecessors. Discussion activity 12 will introduce an alternative algorithm that uses depth-first search instead (which I find more elegant). It turns out that reversing the DFS “settled” order gives a topological order.

Supplemental reading

JavaHyperText: Depth-first and breadth-first search
Myers: Graph traversals

Post-lecture tasks

Take Quiz 12 on Canvas

Lecture 22: Graphs

Required reading

Chapter 29: 29.1–29.10, 29.25–29.26
Chapter 30: 30.1–30.22

Instructor’s notes

We will cover chapters 29 and 30 over the course of two or three lectures. The graph algorithms parts of the chapters are the main sections we skip in this introductory lecture. So for today’s reading you can skip over anything about traversals or shortest paths; we’ll come back to those later. Do concentrate on terminology and on representations.

Supplemental reading

JavaHyperText: graphs, topics 1–3: definitions, terminology, representations
Myers: Graphs

Lecture 21: Synchronization

Required reading

Instructor’s notes

The textbook does not cover concurrency. The Java Tutorial lesson Concurrency is a good reference for this lecture and the previous. For more detail, including lots of examples, read Java Concurrency in Practice. You should be familiar with the following general concepts:

Producer–consumer problems
Ring buffers
Locks (mutexes) and the synchronized keyword
Deadlock
Condition variables: wait() and notifyAll()

Supplemental reading

Myers: Synchronization

Post-lecture tasks

Take Quiz 11 on Canvas

Lecture 20: Concurrency

Required reading

Processes and Threads
Thread Objects (including subsections)
Thread Interference, Memory Consistency Errors

Instructor’s notes

The textbook does not cover concurrency. The Java Tutorial lesson Concurrency is a good reference for this lecture and the next. You should be familiar with the following general concepts:

Threads of execution
Java’s Thread class
Runnable
Concurrent execution via time slicing or parallelism
Race conditions

One inconvenience when experimenting with threads is that blocking operations like sleep(), join(), and wait() could throw InterruptedException, which is a “checked” exception that you must handle before it propagates outside of your Runnable’s run() method. Java does this to support universal thread interruption—if an application needs all of its threads to stop working and clean up so it can exit, it can call interrupt() on all of its Thread objects. Thread runnables are supposed to periodically poll their thread’s interrupted() status to know when to clean up, but if the interrupt occurs while they are blocked, then the blocking method will complete early and throw InterruptedException to let its caller know.

The general rule for handling checked exceptions applies: if the caller knows how to respond to the exception (i.e., how to halt the task and clean up), then it should do so; otherwise, it should propagate the exception by declaring that it, too, throws InterruptedException. It is almost never appropriate to “swallow” the exception and ignore it. In demos, where interrupts will not occur and where no cleanup would be necessary anyway, our preferred approach is to propagate the exceptions up to run(), which will then catch and rethrow them as unchecked RuntimeExceptions. This expresses the intent that they are unexpected while still responding to them in the desired way (stopping the thread).

Supplemental reading

JavaHyperText: concurrency
Myers: Concurrency

Lecture 19: Event-driven programming

Instructor’s notes

Supplemental reading

The Swing Tutorial: Writing Event Listeners
The Swing Tutorial: Concurrency in Swing
Myers: Graphical User Interfaces: Events
The Java Tutorials: Lambda Expressions

Post-lecture tasks

Take Quiz 10 on Canvas
Start working on Assignment 5

Lecture 18: Graphical User Interfaces

Instructor’s notes

Supplemental reading

The Swing tutorial: Using Top-Level Containers
The Swing tutorial: A Visual Guide to Layout Managers
Myers: Graphical User Interfaces: Display and Layout

Lecture 17: Dictionaries and hashing

Required reading

Chapter 20—Dictionaries
Chapter 22—Introducing Hashing: 22.1–22.8, 22.10–22.15, 22.24–22.26
Chapter 23—Hashing as a Dictionary Implementation: 23.1–23.2, 23.6–23.8, 23.16–23.17

Instructor’s notes

The textbook’s treatment of hashing is very “classical” (I have a textbook from 1984 that treats the topic in the same way). In response to the fact that real-world hash codes are not uniformly distributed (which is still true of Java’s hash codes for most built-in types), it advocates for limiting table sizes to prime numbers and dedicates several pages to quadratic probing and double hashing. But there are ways to improve the diffusion of the index derivation process (for example, by computing a quality hash of the original hash code), and with uniformly-distributed indices, these approaches are less relevant in practice. As an example, Java’s HashMap uses tables whose sizes are a power of 2.

Chaining remains a popular and performant approach to collision resolution, but linear probing has seen a resurgence in popularity. Techniques like “Robin Hood hashing” reduce the number of probes necessary to find keys contained within the table, and keeping the probe sequence close to the original index provides good memory locality, allowing clusters to be searched very quickly despite their length.

In section 23.2, the textbook claims that, for probing, elements in the “available” state do not affect the load factor. Unless I’m missing something, this is false—the presence of “tombstones” in a table causes all searches to take longer, so they must be included in the numerator of the load factor definition.

Supplemental reading

JavaHyperText: hash table
Myers: Hash tables

Post-lecture tasks

Take Quiz 9 on Canvas

Lecture 16: Sorting

Required reading

Chapter 15—An Introduction to Sorting: 15.1–15.14
Chapter 16—Faster Sorting Methods: 16.1–16.7, 16.9–16.19, 16.23

Instructor’s notes

Supplemental reading

JavaHyperText: sorting (1, 2)
Myers: Sorting

Lecture 15: Loop invariants

Required reading (JavaHyperText)

Supplemental reading

Myers: Loop invariants

Post-lecture tasks

Take Quiz 8 on Canvas

Lecture 14: Trees II

Post-lecture tasks

Optionally take Quiz 7 on Canvas
Start working on Assignment 4

Lecture 13: Trees I

Required reading

Chapter 24: 24.1–24.17, 24.22–22.24, 24.28–24.31
Chapter 25: 25.1–25.2, 25.9–25.11, 25.18
Chapter 26: 26.1–26.18, 26.40–26.43

Instructor’s notes

Supplemental reading

JavaHyperText: trees (1, 2, 3, 5)
Myers: Trees

Lecture 12: Recursion

Required reading

Chapter 5—Stacks: 5.22
Chapter 9—Recursion

Post-lecture tasks

Take Quiz 6 on Canvas

Supplemental reading

JavaHyperText: recursion (do you get the joke?)
Myers: Recursion
Chapter 14—Problem Solving with Recursion

Lecture 11: Efficiency

Required reading

Chapter 4—The Efficiency of Algorithms
Chapter 19—Searching: 19.1–19.18, 19.21–19.24 (skips recursive searches, for now; will revisit in Lecture 15)

Supplemental reading

JavaHyperText: algorithmic complexity
Myers: Asymptotic complexity

Lecture 10: Ordered collections

Required reading

Chapter 5—Stacks: 5.1–5.4
Chapter 6—Stack Implementations: 6.1–6.12
Chapter 7: 7.1–7.13 (Queue ADT)
Chapter 8: 8.1–8.16 (Queue implementations: linked and array-based)
Chapter 10—Lists
Chapter 11—A List Implementation That Uses an Array: 11.1–11.13
Chapter 12—A List Implementation That Links Data: 12.1–12.24

Post-lecture tasks

Take Quiz 5 on Canvas

Supplemental reading

JavaHyperText: list, linked list, doubly-linked list, stack, queue
Myers: Linked lists

Lecture 9: Linked structures

Required reading

Chapter 3—A Bag Implementation That Links Data

Post-lecture tasks

Start working on Assignment 3

Lecture 8: Generics

Required reading

Introduction—Organizing Data
Chapter 1—Bags
Java Interlude 1—Generics
Chapter 2—Bag Implementations That Use Arrays

Supplemental reading

The Java Tutorials: Generics, Introduction to Collections
JavaHyperText: bag, data structure, abstract data type, generics
Myers: Parametric Polymorphism (generics)

Post-lecture tasks

Take Quiz 4 on Canvas

Lecture 7: Exceptions, I/O

Required reading

Java Interlude 2—Exceptions
Java Interlude 3—More About Exceptions: J3.1–J3.8
Supplement 1—Java Basics: S1.32–S1.37, S1.81–S1.85
Supplement 2—File Input and Output: S2.1–S2.19
Input/output in Java

Supplemental reading

The Java Tutorials: Exceptions, Basic I/O
JavaHyperText: exceptions
Myers: Exceptions

Lecture 6: Inheritance

Required reading

Appendix C—Creating Classes from Other Classes: C.1–C.24
Prelude—Designing Classes: P.21–P.22, P.28–P.31

Post-lecture tasks

Take Quiz 3 on Canvas
Review Assignment 1 feedback
Look up your prelim 1 exam time and mark it in your planner. If you have a conflict, fill out the prelim 1 conflict survey on Canvas

Supplemental reading

The Java Tutorials: Inheritance
JavaHyperText: inheritance, extends, subclass, superclass, bottom-up rule, override, super, this
Myers: Inheritance and the specialization interface

Lecture 5: Interfaces, subtyping

Required reading

Prelude—Designing Classes: P.12–P.20

Post-lecture tasks

Start working on Assignment 2

Supplemental reading

The Java Tutorials: Interfaces
JavaHyperText: interface, compile-time reference rule
Myers: Interfaces and subtyping

Lecture 4: Specifications, testing

Required reading

Appendix A—Documentation and Programming Style: A.1–A.12
Code style

Post-lecture tasks

Take Quiz 2 on Canvas

Supplemental reading

JavaHyperText: class invariant, javadoc comment, specification, precondition, postcondition
Myers: Designing and documenting interfaces, Modular Design and Testing

Lecture 3: Abstraction, encapsulation

Required reading

Prelude—Designing Classes: P.1–P.11
Appendix B—Java Classes: B.17–B.26

Post-lecture tasks

~~Look up your prelim 1 exam time and mark it in your planner. If you have a conflict, fill out the prelim 1 conflict survey on Canvas~~ (postponed due to registrar glitch)

Supplemental reading

JavaHyperText: access modifier, constructor, new-expression…
Myers: Encapsulation and Information Hiding

Lecture 2: Objects

Required reading

Unless linked or otherwise specified, readings refer to chapters and sections from our textbook, Data Structures and Abstractions with Java, Fifth Edition. If you do not have a paper copy, you should be able to access an electronic version via the “Course Materials” link on Canvas.

Appendix B—Java Classes: B.1–B.16, B.22–B.28, B.34–B.35
Java Interlude 6—Mutable and Immutable Objects
Object Diagram Rules

Post-lecture tasks

Take Quiz 1 on Canvas

Supplemental reading

The Java Tutorials: Classes and Objects
JavaHyperText: types 0–2, classes 1A–1C
Myers: Objects and Values

Lecture 1: Course overview

Post-lecture tasks

There are a lot of these after the first lecture, but don’t worry—the pace will even out quickly.

Follow the setup guide to install and configure IntelliJ on your computer
Register your iClicker remote
Read the syllabus (yes, all of it) and take the syllabus quiz on Canvas
If you are new to Java, read the transition to Java guide
Access the textbook’s online supplement 1: Java Basics (this will be assigned reading for the next few lectures, but it is only available online)
Start working on Assignment 1

Required reading

If you are already familiar with Java, you can skim these resources to review any details you may have forgotten. If you are new to Java, these are the resources you should use to learn its procedural syntax (these foundations will not be discussed further in lecture).

Transition to Java
Supplement 1—Java Basics: S1.2–S1.31, S1.38–S1.50, S1.57–S1.63, S1.66–S1.80, S1.86–S1.96

Supplemental reading

Supplemental readings are optional, but they should be the first place you go if a topic is still unclear after reviewing lecture notes and the textbook. They are also valuable if you want to broaden and deepen your knowledge of the material. These curated links are of much higher quality than the top search results on Google.

The Java Tutorials: Language Basics