1 university of utah – school of computing computer science 1021 "programming with...

11University of Utah – School of Computing

Computer Science 1021 "Programming with Style"

University of Utah – School of Computing

University

of Utah

22

No oneprograms

in avacuum.


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of Utah

33

In Real Life...

• Other people will read your code• Other people will maintain your code• Other people will reuse your code in new

programs


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of Utah

44

So...

• Make your programs easy to understand• Don't be too “clever!”


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of Utah

55

Style Tip #1

• Indent consistently


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of Utah

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No Indentationpublic void mousePressed(MouseEvent e) {mousePos = e.getPoint();prevMousePos = mousePos;if (e.getButton() == 1) {if (lassoRect.contains(mousePos)) {return;} for (WhiteboardTeam wt : teams) {WhiteboardCard c = wt.getCardAtPosition(mousePos);if (c != null) {select(c);dragging = true;dnd = false;c.setPrevPosition(c.getPosition());return;}} lassoPos = new Point(mousePos);lassoRect.setLocation(lassoPos);lassoRect.setSize(0,0);setCursor(Cursor.getDefaultCursor());}}


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of Utah

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Bad Indentation public void mousePressed(MouseEvent e) { mousePos = e.getPoint(); prevMousePos = mousePos; if (e.getButton() == 1) { if (lassoRect.contains(mousePos)) { return; } for (WhiteboardTeam wt : teams) { WhiteboardCard c = wt.getCardAtPosition(mousePos); if (c != null) {select(c); dragging = true; dnd = false; c.setPrevPosition(c.getPosition()); return; }} lassoPos = new Point(mousePos); lassoRect.setLocation(lassoPos); lassoRect.setSize(0,0); setCursor(Cursor.getDefaultCursor());}}


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of Utah

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Good Indentationpublic void mousePressed(MouseEvent e) { mousePos = e.getPoint(); prevMousePos = mousePos; if (e.getButton() == 1) { if (lassoRect.contains(mousePos)) { return; } for (WhiteboardTeam wt : teams) { WhiteboardCard c = wt.getCardAtPosition(mousePos); if (c != null) { select(c); dragging = true; dnd = false; c.setPrevPosition(c.getPosition()); return; } } lassoPos = new Point(mousePos); lassoRect.setLocation(lassoPos); lassoRect.setSize(0,0); setCursor(Cursor.getDefaultCursor()); }}


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of Utah

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Style Tip #2

• Use blank lines wisely- between each method- between each important part of a method


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of Utah

1010

Spacingpublic void mousePressed(MouseEvent e) { mousePos = e.getPoint(); prevMousePos = mousePos;

if (e.getButton() == 1) { if (lassoRect.contains(mousePos)) { return; }

for (WhiteboardTeam wt : teams) { WhiteboardCard c = wt.getCardAtPosition(mousePos); if (c != null) { select(c); dragging = true; dnd = false; c.setPrevPosition(c.getPosition()); return; } }

lassoPos = new Point(mousePos); lassoRect.setLocation(lassoPos); lassoRect.setSize(0,0); setCursor(Cursor.getDefaultCursor()); }}


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of Utah

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Style Tip #3

• Don't make methods too long


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of Utah

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Style Tip #4

• Use standard naming conventions- Class names: First letter capitalized- Variable names: First letter lowercase- “final” variables: ALL_CAPS


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of Utah

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Style Tip #5

• Variables on top• Methods below


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of Utah

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Not wrong, just weirdpublic class Person {

public void setMother(Person m) {mother = m;

}

public void setFather(Person f) {father = f;

}

public Person(String n) {name = n;

}

private String name;private Person mother;private Person father;

}


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of Utah

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Ahh... That's better!public class Person {

private String name;private Person mother;private Person father;

public Person(String n) {name = n;

}

public void setMother(Person m) {mother = m;

}

public void setFather(Person f) {father = f;

}}


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of Utah

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Style Tip #6

• Turn big problems into small problems- Divide your program into classes- Put each action in its own method- Minimize public variables


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of Utah

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Style Tip #7

• Comment your code!


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of Utah

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Comment Formats// Single-line comment

/* Multiple Line Comment*/

/* Easier * to read * Multiple * Line * comment */


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of Utah

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Comment Risk #1

// Store the value 5// into the variable x

x = 5;


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of Utah

2020

Comment Risk #2/* Get the two values from the user. * Convert the String input into floating-point * numbers. * We use Java's built-in “parse” methods * to do this. */

String temp = side1TextField.getText();int side1 = Integer.parseInt(temp);temp = side2TextField.getText();float side2 = Float.parseFloat(temp);

/* Now, we compute the hypotenuse of a * right triangle by squaring both sides, * adding them up, then taking the square * root of the sum. */

float side1Squared = side1 * side1;float side2Squared = side1 * side2;float sum = side1Squared + side2Squared;double hypotenuse = Math.sqrt(sum);


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of Utah

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Style Tip #8

• Avoid “magic numbers”!


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of Utah

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Magic Numbers

String message = “”;if (roomNumber == 1)

message = “Welcome to the White Room.”;if (roomNumber == 2)

message = “You tiptoe into the Office.”;if (roomNumber == 3)

message = “This is the Kitchen. Are you hungry?”;if (roomNumber == 4)

message = “You enter the Parlor. Light music is playing.”;if (roomNumber == 5)

message = “Sweating profusely, you enter the Warm Room.”;


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of Utah

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Magic Numbers

final int WHITE_ROOM = 1;final int OFFICE = 2;final int KITCHEN = 3;final int PARLOR = 4;final int WARM_ROOM = 5;

String message = “”;if (roomNumber == WHITE_ROOM)

message = “Welcome to the White Room.”;if (roomNumber == OFFICE)

message = “You tiptoe into the Office.”;if (roomNumber == KITCHEN)

message = “This is the Kitchen. Are you hungry?”;if (roomNumber == PARLOR)

message = “You enter the Parlor. Light music is playing.”;if (roomNumber == WARM_ROOM)



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of Utah

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Style Tip #9

• Use nested “if” statements carefully


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of Utah

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For example...

if (a > b) {if (a > c) {

largest = a;}else {

largest = c;}

}else {

if (b > c) {largest = b;

}else {

largest = c;}

}


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of Utah

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Better!

if (a > b && a > c) {largest = a;

}

if (b > a && b > c) {largest = b;

}

if (c > a && c > b) {largest = c;

}


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of Utah

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Another example...

if (h == 1)house = “Gryffindor”;

else if (h == 2)house = “Slytherin”;

else if (h == 3)house = “Ravenclaw”;

else if (h == 4)house = “Hufflepuff”;


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of Utah

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Improvement?

if (h == 1)house = “Gryffindor”;

else if (h == 2)house = “Slytherin”;

else if (h == 3)house = “Ravenclaw”;

else if (h == 4)house = “Hufflepuff”;


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of Utah

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Still Better...

if (h == 1) {house = “Gryffindor”;

}if (h == 2) {

house = “Slytherin”;}if (h == 3) {

house = “Ravenclaw”;}if (h == 4) {

house = “Hufflepuff”;}


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of Utah

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Yet another way

switch (h) {case 1:house = “Gryffindor”;break;

case 2:house = “Slytherin”;break;

case 3:house = “Ravenclaw”;break;

case 4:house = “Hufflepuff”;break;

}


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of Utah

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Style Tip #10

• Don't optimize prematurely


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of Utah

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Style Tip #11

• Documentation!- Just do it.


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of Utah

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Style Tip #12

• Consistency- dontMix_styles- indent the same everywhere


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of Utah

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Style Tip #13

• Don't be too clever.


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of Utah

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A Quote

• "Consider two programs. One was written by a clever programmer, using all the tricks. The program contains no comments, but it works. The other is nicely commented and well-structured, but doesn't work. Which program is more useful? In the long run, the "broken" one is more useful because it can be fixed and maintained easily. Although the clever one works now, sooner or later it will have to be modified. The hardest work you will ever have to do is modifying a cleverly written program."

From page XV of "Practical C++ Programming" by Steve Oualline


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of Utah

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Example:Operator Precedence

Operators Precedence

postfix expr++ expr--

unary ++expr --expr +expr -expr ~ !

multiplicative * / %

additive + -

shift << >> >>>

relational < > <= >= instanceof

equality == !=

bitwise AND &

bitwise exclusive OR ^

bitwise inclusive OR |

logical AND &&

logical OR ||

ternary ? :

assignment = += -= *= /= %= &= ^= |= <<=>>= >>>=


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of Utah

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Operator Precedence:Simplifed!

• Two rules:- Multiplication and division before addition

and subtraction- Use parentheses for everything else


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of Utah

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And nowfor something

completelydifferent!


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of Utah

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Magic Numbers:Revisited









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of Utah

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roomNumber = -1;


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of Utah

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int weird = OFFICE + KITCHEN;


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of Utah

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A Better Way

enum Room { WHITE_ROOM, OFFICE, KITCHEN, PARLOR, WARM_ROOM

}

String message = “”;if (roomID == Room.WHITE_ROOM)

message = “Welcome to the White Room.”;if (roomID == Room.OFFICE)

message = “You tiptoe into the Office.”;if (roomID == Room.KITCHEN)

message = “This is the Kitchen. Are you hungry?”;if (roomID == Room.PARLOR)

message = “You enter the Parlor. Light music is playing.”;if (roomID == Room.WARM_ROOM)



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of Utah

4343

Enums are safer

Room room1 = Room.OFFICE;Room room2 = Room.KITCHEN;

Room weird = room1 + room2; //ILLEGAL

Room room3 = 3; //ILLEGAL

Room bureau = “OFFICE”; //ILLEGAL


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of Utah

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Coming Tomorrow:

• More advanced features!


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of Utah

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Reminders

• Homework 8 due tomorrow, July 31• FINAL EXAM THURSDAY @ 07:30

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