CS 635 Advanced Object-Oriented Design & Programming Spring Semester, 2001 Assignment 1 Comments
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Standard Issues

Code formatting
Line Wrap
Refactorings to reduce nesting levels

Replace Nested Conditional with Guard Clauses
Decompose Conditional
Introduce Null Object

Comments

Kinds of Comments
Commenting Efficiently
Commenting Techniques

Commenting Individual Lines
Commenting Paragraphs of Code

Commenting Data Declarations
Commenting Routines

Outline of Solution

Problem 3. Visitor
Problem 4 Strategy

Doc 15, Assignment 1 Comments Slide # 2

Standard Issues

public void foo()
{
   code here
}

public void bar() { code here }

public void foobar() {
   code here
}

Doc 15, Assignment 1 Comments Slide # 3

Code formatting

public abstract class HttpTransaction
 {
 HashMap headers = new HashMap();
 byte[] body;
     abstract void  parseFirstLine(ByteReader input ); q 
 abstract String firstLineToString();
   public void fromStream( InputStream input) throws IOException
 {
  ByteReader bufferedInput = new ByteReader( input);
      
parseFirstLine(bufferedInput);
if ( hasHeaders() )
parseHeaders(bufferedInput);
if (hasBody() )
parseBody(bufferedInput);
}
      
   public byte[] toBytes()
    {
   if (!hasBody())
       return toString().getBytes();
      String headerString = toString();
     int length = headerString.length() + body.length;
      byte[]  transaction = new byte[length];  
     System.arraycopy(headerString.getBytes(), 0, transaction, 0, headerString.length());
         System.arraycopy(body, 0, transaction, headerString.length(), body.length);
    return transaction;
      }
      
   public boolean hasContentLength()
      {
      return (headers.containsKey( "Content-length" ) || 
         headers.containsKey( "Content-Length" ));
      } 

Doc 15, Assignment 1 Comments Slide # 4

Line Wrap

   public byte[] toBytes()
      {
      if (!hasBody())
         return toString().getBytes();      //get the string and 
convert it to bytes then return it
      String headerString = toString();//convert to a string
      int length = headerString.length() +
 body.length;
      byte[]  transaction = new byte[length];//declare transaction
      System.arraycopy(headerString.getBytes(), 0, 
transaction, 0, headerString.length());
      System.arraycopy(body, 0, transaction, 
headerString.length(), body.length);
      return transaction;
      }
         {
         String requestLine = readLine(input);      // Read a 
Line of input from the input
         while (requestLine.length() > 0 )
            {
            int separatorIndex = requestLine.indexOf(':');
            String name = requestLine.substring(0, 
separatorIndex);
            String value = 
requestLine.substring(separatorIndex + 1).trim();
            headers.put( name, value);
            requestLine = readLine(input);
Doc 15, Assignment 1 Comments Slide # 5

         String requestLine = readLine(input);      // Read a 
Line of input from the input

• Do not use end of line comments

• Use short expressive name

Doc 15, Assignment 1 Comments Slide # 6

if ( blah ) {
   if (more blah) {
      foo;
   else {
      if ( bar ) {
         not bar
      else {
         if ( more bar ) {
            if (even more bar ) {
               if (still more bar ) {
                  if (even still more bar ) {
                     if ( bar until you can’t stand it ) {
                        if ( foo ) {
                           if ( more foo ) {
                              if ( still more foo ) {
                                 if ( you can understand the nesting level here please do not work for me) {
                                 }
                              }
                           }
                        }
                     }
                  }
               }
            }
         }
      }
Doc 15, Assignment 1 Comments Slide # 7

Doc 15, Assignment 1 Comments Slide # 8

Refactorings to reduce nesting levels

Replace Nested Conditional with Guard Clauses[1]

double getPayAmount() {
   double result;
   if ( _isDead) 
      result = deadAMount();
   else {
      if ( _isSeparated) 
         result = separatedAmount();
      else {
         if (_isRetired) 
            result = retiredAmount();
         else
            result = normalPayAmount();
      }
   }
}

double getPayAmount() {
   if ( _isDead) 
      return deadAMount();
   if ( _isSeparated) 
      return separatedAmount();
   if (_isRetired) 
      return  retiredAmount();
   return normalPayAmount();
}

Doc 15, Assignment 1 Comments Slide # 9

Decompose Conditional[2]

   if (date.before (SUMMER_START) || date.after(SUMMER_END))
      charge = quality * _winterRate + _winterServiceCharge;
   else
      charge = quantity * _summerRate

   if (notSummer( date))
      charge = winterCharge(quantity);
   else
      charge = summerCharge(quantity);
Doc 15, Assignment 1 Comments Slide # 10

Introduce Null Object[4]

void add(int key, String value)
   if (key < _key ) {
      if (right == null)
         left == new BinaryNode(key, value);
      else
         left .add( key, value);
      etc.

void add(int key, String value)
   if (key < _key ) {
      left .add( key, value);
      etc.

Doc 15, Assignment 1 Comments Slide # 11

void add(int key, String value)
   if (key < _key ) {
      if (left == null)
         left = new BinaryNode(key, value);
      else
         left.add( key, value);
   else {
      if (key == _key )
         value = _value;
      else {
         if (key > _key ) {
            if ( right == null ) {
               right = new BinaryNode(key, value);
            else
               left.add( key, value);
         }
      }
   }
}

void add(int key, String value)
   if (key < _key )
      retun left.add( key, value);
   if (key == _key )
      return value = _value;
   if (key > _key ) 
      return left.add( key, value);
}

Doc 15, Assignment 1 Comments Slide # 12

Comments

for i := 1 to Num do
 MeetsCriteria[ i ] := True;
for  i := 1 to Num / 2  do begin
 j := i + i;
 while ( j <= Num ) do begin
  MeetsCriteria[ j ] := False;
  j := j + i;
 end;
for i := 1 to Mun do
 if MeetsCriteria[ i ] then
  writeln( i, ' meets criteria ' );

Doc 15, Assignment 1 Comments Slide # 13

for PrimeCandidate:= 1 to Num do
   IsPrime[ PrimeCandidate] := True;
for  Factor:= 1 to Num / 2  do begin
   FactorableNumber := Factor + Factor ;
   while ( FactorableNumber <= Num ) do begin
      IsPrime[ FactorableNumber ] := False;
      FactorableNumber := FactorableNumber + Factor ;
   end;
end;
for PrimeCandidate:= 1 to Num do
   if IsPrime[ PrimeCandidate] then
      writeln( PrimeCandidate, ' is Prime ' );

Doc 15, Assignment 1 Comments Slide # 14

Kinds of Comments

• Repeat of the code

   X := X + 1    /* add one to X
   /** Integer value */
   private int key;
   /** String value */
   private String value;

• Explanation of code

Used to explain complicated or tricky code

      *p++->*c = a
      /* first we need to increase p by one, then ..

Make code simpler before commenting

      (*(p++))->*c = a
      ObjectPointerPointer++;
      ObjectPointer = *ObjectPointerPointer;
      ObjectPointer ->*DataMemberPointer = a;

Doc 15, Assignment 1 Comments Slide # 15

• Marker in the code

/*  **** Need to add error checking here  **** */

• Summary of the code

Distills a few lines of code into one or two sentences

• Description of the code's intent

Explains the purpose of a section of code

{ get current employee information }   intent
{ update EmpRec structure }     what

Doc 15, Assignment 1 Comments Slide # 16

Commenting Efficiently

• Use styles that are easy to maintain

/***********************************
 * module: Print                   *
 *                                 *
 * author: Roger Whitney           *
 * date:   Sept. 10, 1995          *
 *                                 *
 * blah blah blah                  *
 *                                 *
 ***********************************/
/***********************************
  module: Print          
                         
  author: Roger Whitney  
  date:   Sept. 10, 1995 
                         
  blah blah blah         
                         
 ***********************************/

• Comment as you go along

Doc 15, Assignment 1 Comments Slide # 17

Commenting Techniques

Commenting Individual Lines

MOV AX,  723h        ;    R. I. P. L. V. B.

MemToInit := MemoryAvailable(); { get memory available }

Not much room for comment

Must work to format the comment

Data declarations

Maintenance notes

Mark ends of blocks

Doc 15, Assignment 1 Comments Slide # 18

Commenting Paragraphs of Code

/* if allocation flag is zero */
if ( AllocFlag == 0 ) ...

/* if allocating a new member */
if ( AllocFlag == 0 ) ...

/* if allocating a new member */
if ( AllocFlag == NEW_MEMBER ) ...

Doc 15, Assignment 1 Comments Slide # 19

{ check each character in "InputStr" until a 
  dollar sign is found or all characters have 
  been checked }
Done   := false;
MaxPos := Length( InputStr );
i      := 1;
while ( (not Done) and (i <= MaxLen) ) begin
   if ( InputStr[ i ] = '$' ) then
      Done := True
   else
      i := i + 1
end;

{ find the command-word terminator }
Done   := false;
MaxPos := Length( InputStr );
i      := 1;
while ( (not Done) and (i <= MaxPos ) ) begin
   if ( InputStr[ i ] = '$' ) then
      Done := True
   else
      i := i + 1
end;

Doc 15, Assignment 1 Comments Slide # 20

{ find the command-word terminator }
FoundTheEnd      := false;
MaxCommandLength := Length( InputStr );
Index            := 1;
while ((not FoundTheEnd) and 
       (Index <= MaxCommandLength)) begin
   if ( InputStr[ Index ] = '$' ) then
      FoundTheEnd := True;
   else
      Index := Index + 1;
end;

Doc 15, Assignment 1 Comments Slide # 21

Commenting Data Declarations

var
   CursorX:      1..MaxCols;   { horizontal screen position of cursor }
   CursorY:      1..MaxRows;   { vertical position of cursor on screen }
   AntennaLength:   Real;   { length of antenna in meters: >= 2 }
   SignalStrength:   Integer;   { strength of signal in kilowatts: >= 1 }
   CharCode:      0..255;   { ASCII character code }
   CharAttib:      Integer;   { 0=Plain; 1=Italic; 2=Bold  }
   CharSize:         4..127;   { size of character in points }
Comment limitations on input data
Document flags to the bit level

Doc 15, Assignment 1 Comments Slide # 22

Commenting Routines

procedure InsertionSort 
   {
   Var   Data:      SortArray;    { sort array elements }
      FirstElement:   Integer        {index of first element to sort}
      LastElement:   Integer        {index of last element to sort}
   }

Doc 15, Assignment 1 Comments Slide # 23

//*****************************************************
//*****************************************************
// Class: Proxy
//*****************************************************
//*****************************************************
public class Proxy {
   //***************************************************
   //Default Constructor
   //***************************************************
   public Proxy() { blah }
   //***************************************************
   //Constructor
   //***************************************************
   public Proxy(int size) {
   _size = size;}
   //***************************************************
   //Main
   //***************************************************
   public static void public static void main( String[] args ) {
      //Create a new socket
      ServerSocket acceptor = new ServerSocket(0);
      //Print out the port number
      System.out.println("On port " + acceptor.getLocalPort());
      while (true) {//runs forever, until program is manually killed
         Socket client = acceptor.accept();//Accept a new connection
         processRequest(//Process the client request 
            client.getInputStream(),//get the input
            client.getOutputStream());//get the ouput
         client.close();//Close the connection

Doc 15, Assignment 1 Comments Slide # 24

public class Proxy 
   {

   public Proxy() 
      { 
      blah 
      }

   public Proxy(int size) 
      {
      _size = size;
      }

   public static void public static void main( String[] args ) 
      {
      ServerSocket acceptor = new ServerSocket(0);
      System.out.println("On port " + acceptor.getLocalPort());

      //Must kill process to terminate
      while (true) 
         {
         Socket client = acceptor.accept();
         processRequest( 
            client.getInputStream(),
            client.getOutputStream());
         client.close();
         }
      }
   }

Doc 15, Assignment 1 Comments Slide # 25

//-------------------------------------------------------------

public class Proxy 
   {

   public Proxy() 
      { 
      blah 
      }

   public Proxy(int size) 
      {
      _size = size;
      }

   public static void public static void main( String[] args ) 
      {
      ServerSocket acceptor = new ServerSocket(0);
      System.out.println("On port " + acceptor.getLocalPort());

      //Must kill process to terminate
      while (true) {
         Socket client = acceptor.accept();
         processRequest( 
            client.getInputStream(),
            client.getOutputStream());
         client.close();

Doc 15, Assignment 1 Comments Slide # 26

thisIsTheJavaStandardNameStyleForMethodNamesAndVariables

ClassName

Doc 15, Assignment 1 Comments Slide # 27

public Interator interator(int order) 
   {
   switch(order)
      {
      case PREORDER:
         return new PreorderInterator(this);
      case INORDER:
         return new InorderInterator(this);
      default:
         throw new IllegalArgumentExeption("No such order");
      }
   }

public Interator preorderInterator() 
   {
   return new PreorderInterator(this);
   }

public Interator inorderInterator() 
   {
   return new InorderInterator(this);
   }

Doc 15, Assignment 1 Comments Slide # 28

abstract class Visitor
   {
   Node root;
   abstract void visitTree(BinaryTree visitee);
   abstract void visitNode(Node visitee);
   }

class PreorderVisitor extends Visitor
   {
   Node root;
   blah
   etc.
   }

Doc 15, Assignment 1 Comments Slide # 29

abstract class Visitor
   {
   abstract void visitTree(Node visitee);
   abstract void visitNode(Node visitee);
   }

class PreorderVisitor extends Visitor
{
   Node root;
   blah
   etc.
}

Doc 15, Assignment 1 Comments Slide # 30

public class BinaryTreeIterator implements Iterator{
   public static final int PREORDER = 1;
   public static final int INORDER = 2;
   int type;
   public boolean hasNext() {
      blah
      if (PREORDER  == type)
         do the preorder thing
      else if (INORDER == type)
         do the inorder thing
      else
         now what?
      more blah
   }
   public Object next() {
      blah
      if (PREORDER  == type)
         do the preorder thing
      else if (INORDER == type)
         do the inorder thing
      else
         now what?
      more blah
   }
}

Doc 15, Assignment 1 Comments Slide # 31

Outline of Solution

• BinarySearchTree
• Node (interface)
• BinaryNode
• NullNode

• PreorderIterator
• InorderIterator

Doc 15, Assignment 1 Comments Slide # 32

Problem 3. Visitor

class BinarySearchTree {
   public accept(Visitor visitor) {
      visitor.visitBinarySerachTree( this);
      root.accept( visitor);
   }
}
   
class BinaryNode{
   public accept(Visitor visitor) {
      visitor.visitBinaryNode( this);
      left.accept( visitor);
      right.accept( visitor);
   }
}
   
class NullNode{
   public accept(Visitor visitor) {
      visitor.visitNullNode( this);
   }
}

Doc 15, Assignment 1 Comments Slide # 33

class Visitor {
   integer count = 0;
   
   public visitBinarySerachTree(BinarySerachTree tree) {
   }
   
   public visitBinaryNode(BinaryNode node) {
      count++;
      reverseValue( node);
   }
   
   public visitNullNode(BinaryNode node) {
      count++;
   }
   private void reverseValue(BinaryNode node) {
      put your code here
   }
}

Doc 15, Assignment 1 Comments Slide # 34

class BinarySearchTree {
   public accept(Visitor visitor) {
      visitor.visitBinarySerachTree( this);
   }
}
   
class BinaryNode{
   public accept(Visitor visitor) {
      visitor.visitBinaryNode( this);
   }
}
   
class NullNode{
   public accept(Visitor visitor) {
      visitor.visitNullNode( this);
   }
}

BinarySearchTree studentNames;
   
Code here to populate the tree
   
Visitor reverseNames = new Visitor();
studentNames.accept( reverseNames  );

Doc 15, Assignment 1 Comments Slide # 35

class Visitor {
   integer count = 0;
   
   public visitBinarySerachTree(BinarySerachTree tree) {
      Node root = tree.root();
      root.accept( this );
   }
   
   public visitBinaryNode(BinaryNode node) {
      count++;
      reverseValue( node);
      Node left = node.left();
      left.accept( this );
      Node right = node.right();
      right.accept( this );
   }
   
   public visitNullNode(BinaryNode node) {
      count++;
   }
   private void reverseValue(BinaryNode node) {
      put your code here
   }
}
Doc 15, Assignment 1 Comments Slide # 36

   public visitBinaryNode(BinaryNode node) {
      count++;
      reverseValue( node);
      if ( node.left() != null );
         visitBinaryNode( node.left() );
      if ( node.right() != null );
         visitBinaryNode( node.right() );
   }

   public visitBinaryNode(BinaryNode node) {
      count++;
      reverseValue( node);
      Node left = node.left();
      left.accept( this );
      Node right = node.right();
      right.accept( this );
   }

Doc 15, Assignment 1 Comments Slide # 37

Problem 4 Strategy

class Visitor {
   integer count = 0;
   Iterator traversal;
   public Visitor(Interator order) {
      traversal = order;
   }
   
   public visitBinarySerachTree(BinarySerachTree tree) {
      order.on( tree );
      while ( order.hasNext() ) {
         Node next = (Node) order.next();
         next.accept( this );
      }
   }
   
   public visitBinaryNode(BinaryNode node) {
      count++;
      reverseValue( node);
   }
   
   public visitNullNode(BinaryNode node) {
      count++;
   }
   private void reverseValue(BinaryNode node) { 
      blah
   }
}

Doc 15, Assignment 1 Comments Slide # 38

BinarySearchTree studentNames;
   
Code here to populate the tree
   
Visitor reverseNames = new Visitor( new InorderIterator() );
studentNames.accept( reverseNames  );

Doc 15, Assignment 1 Comments Slide # 39

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