Questions

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• Quiz?
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Concept: Loop algorithms applied to ArrayLists

When we talked about loops, we looked at several algorithms. They are very useful when working with ArrayLists

• Finding sum and average
• Maximum and minimum
• Counting matches
• Finding the first match

Concept: Finding the sum

• General algorithm to find the sum of items in a ArrayList

      declare and initialize a variable to hold the sum
      for each element in the ArrayList
           add this value the sum
      

Activity - ArrayList of objects: sum

Record your participation in Piazza clicker question Lesson16 Q1

• We are going to work with an array list of Circle objects.
• Download the starter file. It contains a Circle class (provided), a CircleManager class (started), and a CircleManagerTester (provided). CircleManager has stubs for several ArrayList methods
• First look at the classes we are given
• Pseudocode to find the sum of the areas

      declare and initialize a variable to hold the sum
      for each element in the ArrayList (Use an enhanced for loop)
          get the area of the Circle         
          add the area of this Circle to the sum
      

• Now complete method sumAreas in CircleManager that returns the sum of all the areas. Use an enhanced for loop
• Run the tester
• Did it work?

Activity - ArrayList of objects: average

Record your participation in Piazza clicker question Lesson16 Q2

• How do you calculate an average?
• For our circle_arraylist project, we have the sum of all the areas of the Circles
• How will you get the number of areas?
• Complete the method averageArea to return the average area or 0 if array list is empty.
  • Do not calculate the sum again. Let sumAreas do it for you.
• Uncomment the code in the tester that prints the average
• Run it
• Look at your output for the empty array list
  • Did you get NaN instead of 0?
  • That means you divided by 0
• How do you fix that?

Concept: Finding the maximum

• General algorithm for finding the largest item in a data set

  initialize a variable max to the first element in the list
    for each element 
        if this element is larger than the max
            max = this element

Activity - ArrayList of objects: Largest

Record your participation in Piazza clicker question Lesson16 Q3

• Complete the method largest in CircleManager to get the largest Circle. If the ArrayList is empty, return null
• Uncomment the code in the tester that prints that Circle
• Run it.
  • Does you code work correctly when the ArrayList is empty?
• If your code throws an exception, how do you fix it?

Concept: Finding the first match

  set a boolean flag found to false
  initialize a variable first 
  initialize a loop control variable index to 0
  while there are more elements to look at and !found 
     if this element is a match
        set first to this element
        set found to true
     else
        increment index 

Activity - ArrayList of objects: find first match

Record your participation in Piazza clicker question Lesson16 Q4

• Complete the method firstRadiusGreaterThan10 to get the first Circle with a radius greater than 10. If the ArrayList is empty or does not have an Circle with a radius greater than 10, return null
• Uncomment the code in the tester that prints the first Circle with a radius > 10

Activity - ArrayList of objects: count

Record your participation in Piazza clicker question Lesson16 Q5

• Add a method to get the number of Circles with a radius greater than 1. Call it countRadiusGreaterThanOne. If the ArrayList is empty, return 0. You will need to provide the method header this time.
• Add code to the tester to call the method and print that count

Activity - ArrayList of objects: find all matches

Record your participation in Piazza clicker question Lesson16 Q6

• Add a method that returns an array list containing all the Circles with radius greater than or equal to 10. Call it radiusGreaterOrEqualTo10. You need to write the method header
• Add code to the tester to call the method and print the ArrayList