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Read me that page, Daddy! -Shoshanna Hertz. CSC 313 – Advanced Programming Topics. Lecture 4: Communication. Strategy Pattern Review. Define interface for family of algorithms Signature creates data used by entire family Make each Strategy interchangeable

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Read me that page, Daddy!

-Shoshanna Hertz

Strategy pattern review
Strategy Pattern Review

  • Define interface for family of algorithms

    • Signature creates data used by entire family

  • Make each Strategy interchangeable

    • Encapsulate one in its own class

  • Separate Strategy from its Context

    • Can change Strategy used dynamically

    • Add new Strategies without modifying code

    • Can also reuse Strategy in new environments

public interface Greeter {public void greet(String name);


public class Formal implements Greeter {public void greet(String name) {System.out.println(“Hello ” + name);}


public class Informal implements Greeter {public void greet(String name) {System.out.println(“Hiya ” + name);}


public class French implements Greeter {public void greet(String name) {System.out.println(“Bonjour ” + name);}


public interface Greeter {public void greet(String name);


public abstract class Interpersonal {protected Greeter g;


public class Worker extends Interpersonal {private String person;public void greet() { g.greet(person); }


public class DrHertz extends Interpersonal {public void greet() { g.greet(“Bob”); }


public class Flanders extends Interpersonal {private String person; public void greet() { g.greet(person + “doodly”);}


Shared vocabulary necessary2
Shared Vocabulary Necessary

  • Hints:







    Full of hubris

    Person assigning grades

Shared vocabulary necessary3
Shared Vocabulary Necessary

  • Hints:



    Waste of Time

    Former TRL Host

    Dr. Hertz’s odd fascination

Not a free gift
Not a Free Gift

  • Design patterns are useful…

    • Provide usable design solutions

    • Enable shared vocabulary

  • … but are not panacea

    • Do not prevent complex designs

    • Cannot eliminate bugs

    • Are not “gift” in the box

Brevity is the soul of wit
Brevity is the soul of wit

The competent programmer is fully aware of the strictly limited size of his own skull; therefore he approaches the programming task in full humility, and among other things he avoids clever tricks like the plague.

Edsger Dijkstra

Spot the bug
Spot the Bug

public boolean isPrime(int n) {for (int i = 2; i < n; i++) { if ((n % i) == 0) { return false; }}return true;


public boolean isPrime(int n) {for (int i = 1; i < n; i++) { if ((n % i) == 0) { return false; }}return true;


Spot the bug1

} catch (IOException ioe) {

if ( n == 0 ) {

spec.harness.Context.out.println("Empty database");



spec.harness.Context.out.println("ERROR opening/reading input file \""+filename+"\"");

// System.exit(1);


entry = new Entry();

spec.harness.Context.out.print("OK\nBuilding database ...");


n = buffer.length;

s = e = 0;

while ( (e < n) && (s < n) ) {

// Check for CR also - rrh 2/18/98

while ( (e < n) && (buffer[e] != '\n') && (buffer[e] != '\r') ) e++;

if ( e < n ) {

if ( buffer[s] == '#' ) {


entry = new Entry();

} else

entry.items.addElement(new String(buffer, 0, s, e-s));

// Discard CR & LF - rrh 2/18/98

Spot the Bug

public void read_db(String filename) {

Entry entry;

int i;

int n = 0, act = 0, e, s;

boolean OK;

byte buffer[] = null;

spec.harness.Context.out.print("Reading database "+dbname+" ... ");


try { sif = new;

n = sif.getContentLength();

buffer = new byte[n];

int bytes_read;

while ( (bytes_read =, act , (n - act))) > 0){

act = act + bytes_read;



sif = null; // 03/11/98 rrh

if ( act != n ){

spec.harness.Context.out.println("ERROR reading input file");




Brevity is the soul of wit1
Brevity is the soul of wit

Complexity kills. It sucks the life out of developers, it makes products difficult to plan, build and test, it introduces security challenges and it causes end-user and administrator frustration.

Ray Ozzie

Elevator talk
Elevator Talk

  • Big name in field (or company VP) gets in your elevator asks, “What are you working on?”

    • You duration of elevator ride to explain it all

    • Need to impress, but not BS

  • Boss comes by and asks, “How is it going?”

    • Does not care/have time to get into details

    • Have 90 seconds to get out important issues

This does matter
This Does Matter

  • Need to market your ideas and designs

    • Requires explaining to lazy, impatient coders

    • Get bored well before 90 seconds are up

  • If cannot explain design in elevator talk

    • Code created from design will have bugs

    • Will require major effort to get to work


More marketing
More Marketing

  • This also matters for documentation

  • Bad versus good documentation

More marketing1
More Marketing

  • Documentation must be brief

    • Provides only necessary details

    • Details “needed” only to get user coding

      Before software can be reusable it first has to be usable.

      -- Ralph Johnson

      An API that isn't comprehensible isn't usable.

      -- James Gosling

Why comments are useful
Why Comments are Useful

If the code and the comments disagree, then both are probably wrong.

Norm Schryer

Why comments are useful1
Why Comments are Useful

As you're about to add a comment, ask yourself, 'How can I improve the code so that this comment isn't needed?' Improve the code and then document it to make it even clearer.

Steve McConnell

And finally
…and finally

For every complex problem there is an answer that is clear, simple, and wrong.

-- H L Mencken

Computers are useless. They can only give you answers.

-- Pablo Picasso

For next lecture
For Next Lecture

  • Two (short) readings available on web

    • Will start looking into how code is optimized

    • Begin by investigating how programs actually run

    • Also look at some of the simplest optimizations

    • Important to understand to improve code written

  • There is lab assignment this week

    • Posted to web/Angel

    • Will be due before lab in two weeks