Comp 110 Recitation 3

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Comp 110Recitation 3

• Instructor Sasa Junuzovic

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Agenda

• Stepwise refinement high-level to lower-level
• Internal vs. external calls
• Eclipse Introduction
• Creating a basic project
• Add class to project
• Multiple function calls
• Stepthrough using Eclipse

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Algorithm

• Description of solution to a problem.
• Can be in any language
• graphical
• natural or programming language
• natural programming language (pseudo code)
• Can describe solution to various levels of detail

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Pound Inch BMI Calculator
Weight in pounds
Height in inches
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Steps for Reusing ABMICalculator

• Calculate weight in Kgs from weight in Pounds
• Calculate height in Metres from height in inches
• Call calculateBMI() of ABMICalculator with these
  values
• Return the value returned by this call

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2nd Level Algorithm

• Calculate weight in kgs from weight in Pounds
• Divide weight in Pounds by 2.2
• Calculate height in Meters from height in inches
• Calculate height in centimeters from height in
  inches and divide it by 100 to get height in
  meters
• Call calcuateBMI() of ABMICalculator with these
  values
• Return the value returned by this call

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3rd Level Algorithm

• Calculate weight in kgs from weight in Pounds
• Divide weight in Pounds by 2.2
• Calculate height in metres from height in inches
• Calculate height in centimetres from height in
  inches and divide it by 100 to get height in
  metres
• Multiply height in Inches by 2.54 to get height
  in centimetres
• Call calcuateBMI() of ABMICalculator with these
  values
• Return the value returned by this call

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Stepwise Refinement
Programming Language Algorithm public class
APoundInchBMICalculator () public double
calculateBMI( double weightInLbs,
double heightInInches) return (new
ABMICalculator()).calculateBMI(
weightInLbs/2.2, heightInInches2.54/100)

Does not reflect 3rd-level algorithm instead of
a single function, we need a function for each
level of the algorithm
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External Method Invocation Syntax
Caller and callee methods are in different objects
Example from an instance of class B call
methodInA() in an instance of class A
(new A()).methodInA (p1, p2)
Target Object
Method Name
Actual Parameters
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Internal Method Invocation Syntax
Caller and callee methods are in the same object
Example from an instance of class A call
methodInA() in an the same instance of class A
this.methodInA (p1, p2)
Target Object
Method Name
Actual Parameters
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External vs. Internal Method Invocation Syntax
External
(new A()).methodInA (p1, p2)
Actual Parameters
Method Name
Target Object
Internal
methodInA (p1, p2)
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Multi-Level Code (Edit)
public class APoundInchBMICalculator public
double calculateBMI( double weightInLbs, double
heightInInches)
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Multi-Level Code (Edit)
public class APoundInchBMICalculator
public double calculateBMI( double weightInLbs,
double heightInInches) return (new
ABMICalculator()).calculateBMI( toKgs(weightInLb
s), toMetres(heightInInches))
public double toMetres(double heightInInches)
return toCentiMetres(heightInInches)/100
public double toCentiMetres(double
heightInInches) return heightInInches2.54
public double toKgs(double weightInLbs)
return weightInLbs/2.2
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Eclipse