CS 535: Object-Oriented Programming & Design

1. Reference
2. Conceptual Level Definition
3. Some Typical Beginner Mistakes

Doc 5, Conceptual OO Definition Slide # 1

• Abstraction

"Extracting the essential details about an item or group of items, while ignoring the unessential details."

Edward Berard

What is it?

Can you describe it with a simple sentence?

It contains data and operations (behavior)on the data

• Encapsulation

Enclosing all parts of an abstraction within a container

• Information Hiding

Hiding parts of the abstraction

• Hierarchy

Abstractions arranged in order of rank or level

Doc 5, Conceptual OO Definition Slide # 2

"A stack is a linear list for which all insertions and deletions are made at one end of the list"

pop, push, isEmpty, isFull

Doc 5, Conceptual OO Definition Slide # 3

class Stack[1]  {
   private float[] elements;
   private int topOfStack = -1;
   
   public Stack( int stackSize )  {
      elements = new float[ stackSize ];
   }
   
   public void push( float item )  {
      elements[ ++topOfStack ] = item;
   }
   
   public float pop()  {
      return elements[ topOfStack-- ];
   }
   
   public boolean isEmpty()  {
      if ( topOfStack < 0 )    return true;
      else               return false;
   }
   
   public boolean isFull()  {
      if ( topOfStack >= elements.length )    return true;
      else                           return false;
   }
}

   Stack me = new Stack( 20 );
   me.push( 5 );
   me.push( 12 );
   System.out.println( me.pop() );
   System.out.println( me.pop() );
Doc 5, Conceptual OO Definition Slide # 4

struct Stack 
{
   float stack[100];      
   int topOfStack;
};

void push(Stack& it, int item) 
{  
   it.stack[(it.topOfStack)++] = item;   
}

float pop(Stack& it)
{  
   return it.stack[--(it.topOfStack)];   
}

main()
{
   Stack tryThisOut; 
   Stack yours, mine;

   tryThisOut.topOfStack = 0;
   yours.topOfStack = 0;

   push( tryThisOut, 5.0 );
   push( yours, 3.3 );
   push( tryThisOut, 9.9 );

   cout << pop( tryThisOut ) << endl;
}

Doc 5, Conceptual OO Definition Slide # 5

Data is encapsulated

Operations are not encapsulated with data

The boundaries of what it is become fuzzy

Composability

Understandability

Continuity

Data is not hidden

Data is not safe!

   Stack troubleAhead;

   troubleAhead.topOfStack = 13;
   troubleAhead.stack[ 8 ] = 29;

Doc 5, Conceptual OO Definition Slide # 6

class StackData
{
   public  float[]  elements = new float[100];
   public  int   topOfStack      = 0;
}

class Test
{
   static void push(Stack it, int item) 
   {  
      it.stack[ ( it.topOfStack )++ ] = item;   
   }

   static float pop(Stack it)
   {  
      return it.stack[--(it.topOfStack)];   
   }

   public void static main( String[] args)
   {
      Stack yours, mine;

      push( yours, 3.3 );
      push(  mine, 9.9);
   }

Doc 5, Conceptual OO Definition Slide # 7

class StackData
{
   private  float[]  elements = new float[100];
   private  int        topOfStack      = -1;

   public int getTopOfStack()
   {
      return topOfStack;
   }

   public void setTopOfStack( int newTop )
   {
      topOfStack = newTop;
   }
   
   public float getElement( int elementIndex )
   {
      return elements[ elementIndex ];
   }

   public void getElement( int elementIndex, float element )
   {
      elements[ elementIndex ] = element;
   }
}

Doc 5, Conceptual OO Definition Slide # 8

class Stack {
   private float[] elements = new float[ 100 ];
   private int topOfStack = -1;
   
   public void push( )  
   {
      float item = Console.readFloat( "Type a float to push");
      elements[ ++topOfStack ] = item;
   }
   
   public void  pop()  
   {
      Console.println( "Top stack item: " + 
         elements[topOfStack--];
   }
}

class Test
{
   public void static main( String[] args)
   {
      Stack yours ohNo = new Stack();

      ohNo.push(  );
      ohNo.push(  );
      ohNo.pop(  );
   }

Doc 5, Conceptual OO Definition Slide # 9

• All data should be hidden within its class

• A class should capture one and only one key abstraction

• Keep related data and behavior in one place

• Beware of classes that have many accessor methods in their public interface. This implies data and behavior are not in one place

Doc 5, Conceptual OO Definition Slide # 10

( 3 + 9 - 13 ) * 6 + 2

becomes

3 9 + 13 - 6 * 2 +

read next token

if token is operand push on stack

if token is operator

pop two items off the stack

apply operator to the items from stack

push result on stack

repeat until no more tokens

result is on the top of the stack

Doc 5, Conceptual OO Definition Slide # 11

class CalculatorEngine
{
   private Stack operands = new Stack( 100 );
   
   public float evaluate( String expression )
   {
      StringTokenizer tokenList = 
            new StringTokenizer( expression );
   
      while ( tokenList.hasMoreTokens() )
         processToken( tokenList.nextToken() );
      
      return    operands.pop();
   }
   
   private void processToken( String token )
   {
      if ( token.equals( "+" ) )
         operands.push( operands.pop() + operands.pop() );
         
      else if ( token.equals( "-" ) )
         operands.push( operands.pop() - operands.pop() );
         
      else if ( token.equals( "/" ) )
         operands.push( operands.pop() / operands.pop() );
         
      else if ( token.equals( "*" ) )
         operands.push( operands.pop() * operands.pop() );
      
      else
         operands.push( stringToFloat( token ) );
   }

   private float stringToFloat( String number )
   {
      return Float.valueOf( number ).floatValue();
   }
}
Doc 5, Conceptual OO Definition Slide # 12

class CalculatorGUI
{

   CalculatorEngine rpnEvaluator;

   public CalculatorGUI( CalculatorEngine myComputeEngine )
   {
      rpnEvaluator = myComputeEngine;

      // code to build the gui interface removed
   }

   // code to make gui run removed
}

public static void main( String[] arguments )
{
   CalculatorGUI fourBanger;

   fourBanger = new CalculatorGUI( new CalculatorEngine() );
}
Doc 5, Conceptual OO Definition Slide # 13

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Doc 5, Conceptual OO Definition Slide # 14

Identify the data and the operations on the data

These start to form the classes

Determine how classes interact

Create program on top of the classes

visitors since 17-Sep-97