LECTURE 4:COMMUNICATION

CSC 313 – Advanced Programming Topics

Why Does This Matter?

Spot the Bugpublic 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+" ... "); spec.harness.Context.out.flush(); try { spec.io.FileInputStream sif = new spec.io.FileInputStream(filename); n = sif.getContentLength(); buffer = new byte[n]; int bytes_read; while ( (bytes_read = sif.read(buffer, act , (n - act))) > 0){ act = act + bytes_read; } sif.close(); sif = null; // 03/11/98 rrh if ( act != n ){ spec.harness.Context.out.println("ERROR reading input file"); //System.exit(1); return; }

} catch (IOException ioe) { if ( n == 0 ) { spec.harness.Context.out.println("Empty database"); return; } 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 ..."); spec.harness.Context.out.flush(); 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] == '#' ) { add(entry); entry = new Entry(); } else entry.items.addElement(new String(buffer, 0, s, e-s)); // Discard CR & LF - rrh 2/18/98…

Brevity is the soul of witComplexity 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

Spot the Bug

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

}

Spot the Bug

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

}

Which Line Is Yours?

Shared Vocabulary Necessary Hints:

WiseCreativeHumorousAttractiveImpatientLazyFull of hubrisPerson assigning grades

Shared Vocabulary Necessary Hints:

ToolUselessLack of talentWaste of TimeAI HostDr. Hertz’s odd fascination

Shared Vocabulary Necessary

Shared Vocabulary Necessary

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”);}

}

Strategy Pattern

Define interface for family of algorithms Method signature created for entire

family Coded up so each Strategy

interchangeable Each algorithm encapsulated in class of

its own Separates the Behavior from

Context Implies client uses 1 strategy at a time Also implies can change Strategy

dynamically

Shared Vocab. Not Sufficient

Brevity is the soul of witThe 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

Not a Free Gift

Design patterns are useful… Provide solutions at design level Enable shared vocabulary

… but are not panacea Do not prevent complex designs Programs continue having box

Not a Free Gift

Design patterns are useful… Provide solutions at design level Enable shared vocabulary

… but are not panacea Do not prevent complex designs Programs continue having box Are not “gift” in the box

Elevator Talk

VIP in elevator asks, “What are you working on?” You have elevator ride to explain it all Need to impress, but will lose them with 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 Matters

Need to market your ideas & designs Requires explaining to lazy, impatient

coders Well before your time is up, they are

bored If cannot explain design in elevator

talk Code created from design will have bugs Will require major effort to get to work

This Matters

Need to market your ideas & designs Requires explaining to lazy, impatient

coders Well before your time is up, they are bored

If cannot explain design in elevator talk Code created from design will have bugs Will require major effort to get to work Coders are lazy and HATE effort and work

This Matters

Need to market your ideas & designs Requires explaining to lazy, impatient

coders Well before your time is up, they are

bored If cannot explain design in elevator

talk Code created from design will have bugs Will require major effort to get to work Coders are lazy and HATE effort and

work

IT IS TOO COMPLEX

More Marketing

Explanations must be brief Coders should not see only necessary details Detail needed to code or not an important

details

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

If the code and the comments disagree,

then both are probably wrong.

Norm Schryer

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

Your Turn

Give elevator speech on your current project

…and finally

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

wrong.-- H L Mencken

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