Questions

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Concept: Declaring an ArrayList

• An ArrayList is an improved array
• An ArrayList is similar to a vector in C++ or lists in Python
  • a sequence of values that can be accessed by an integer index
  • Index numbers start at 0
• You can declare an empty ArrayList and assign it to a variable
• To use ArrayLists: import java.util.ArryaList;
• Example

  ArrayList<Rectangle> boxes = new ArrayList<Rectangle>();
  

• Example

  ArrayList<String> professors = new ArrayList<String>();

• Contents of the boxes: [ ]
  • boxes.size() is 0
• Contents of professors: [ ]
  • professors.size() is 0

Concept: Adding to an ArrayList

• To add an element to the end of an ArrayList

  professors.add("Horstmann");
  professors.add("O'Brien");

• Contents: [Horstmann, O'Brien]
• To add an element at a particular index

  professors.add(0,"Heller");

• Contents: [Heller, Horstmann, O'Brien]
• To set (replace) a particular element

  professors.set(1,"Kim");

• Contents: [Heller, Kim, O'Brien]

Concept: More ArrayList methods

• Let's go back to out professors list: Contents: [Heller, Kim, O'Brien]
• To get the element at index i

  String name = professors.get(i);

• To get the number of elements

  int size = professors.size()

• The last element is at size() - 1
• To get the last element

  String last = professors.get(professors.size() - 1);

• To remove the element at index 1

  String name = professors.remove(1);

  • Contents of professors: [Heller, O'Brien]
  • Contents of name: Kim

Concept: Enhanced for loop

• Let's go back to out professors list: Contents: [Heller, O'Brien]
• Add a couple of more professors

  professors.add("Wesley");
  professors.add("Stamp");

• Contents: [Heller, O'Brien, Wesley, Stamp]
• Process using the enhanced for loop

  for (String p: professors)
  {
      //process the element p
  }

Activity - Using an ArrayList

Record your participation in Piazza clicker question Lesson12 Q1

• Write an application that declares an array list of Strings called flowers
• To the array list, add: rose, violet, pansy, zinnia
• Insert lavender in the next to the last position
• Remove element at index 1.
• Now replace each element so it start with an uppercase letter
  • You need to use a traditional for loop since you are changing the ArrayList
• Print the array list on one line without using a loop (page 345. section 7.7.1)
• What is printed?

1. [rose, violet, pansy, zinnia]
2. [Rose, Violet, Pansy, Lavender, Zinnia]
3. [Rose, Pansy, Lavender, Zinnia]
4. [Rose, Violet, Pansy, Lavender]

Activity - ArrayList of objects: sum

Record your participation in Piazza clicker question Lesson12 Q2

• We are going to work with an ArrayList of Circle objects.
• Download the starter file. It contains a Circle class, a CircleManager class (started), and a CircleManagerTester
• Add a method sumAreas that returns the sum of all the areas or 0 if the ArrayList is empty.
• Run the tester

1. Got it
2. Got it but it was hard
3. Couldn't do it in the time allowed
4. Didn't know where to start

Activity - ArrayList of objects: average

Record your participation in Piazza clicker question Lesson12 Q3

• Add a method averageArea to return the average area or 0 if array list is empty.
• Do not calculate the sum in this method (use the previous method)
  • Uncomment the code in the tester that prints the average and run the tester

1. Got it
2. Got it but it was hard
3. Couldn't do it in the time allowed
4. Didn't know where to start

Activity - ArrayList of objects: Largest

Record your participation in Piazza clicker question Lesson12 Q4

• Add a method to CircleManager to get the largest Circle. If the ArrayList is empty, return null
  • Uncomment the code in the tester that prints the Circle and run it

1. Got it
2. Got it but it was hard
3. Couldn't do it in the time allowed
4. Didn't know where to start

Activity - ArrayList of objects: find all matches

Record your participation in Piazza clicker question Lesson12 Q5

• Add a method that returns an ArrayList containing all the Circles with radius greater than or equal to 10. Call it radiusGreaterThan10.
  • Add code to the tester to print the ArrayList

1. Got it
2. Got it but it was hard
3. Couldn't do it in the time allowed
4. Didn't know where to start

Activity - ArrayList of objects: find first match

Record your participation in Piazza clicker question Lesson12 Q6

• Add a method to get the first Circle with a radius greater than 10. Call it firstRadiusGreaterThan10. 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 that Circle

1. Got it
2. Got it but it was hard
3. Couldn't do it in the time allowed
4. Didn't know where to start