Questions

• Reading?
• Interactivities?
• Homework?

Concept: Declaring an ArrayList

• An ArrayList is a sequence of values that can accessed by an integer index
• Index numbers start at 0
• A data structure
• You can declare an empty ArrayList and assign it to a variable
• Example

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

• Example

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

• Contents of the ArrayList: [ ]
• To use ArrayLists: import java.util.ArryaList;

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]

Activity - An ArrayList

Record your participation in Piazza clicker question Lesson15 Q1

Let's work with an array list containing string flower names

• Start a new Bluej Project
• Declare and initialize an array list of strings called garden
• Did you remember the type parameter <String>?
• Does it compile? If not, fix it
• Add "rose", "daisy", and "violet" in that order
• Print the array list
  

  System.out.println(garden); 

• Add "petunia" at position 0
• Add "pansy" at position 2
• What should the list look like now?
• Print it

Concept: More ArrayList methods

• Let's go back to out professors list: Contents: [Heller, Kim, O'Brien]
• To get the element at index 0

  String name = professors.get(0);

• 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

  professors.remove(1);

• Contents: [Heller, O'Brien]

Activity - More array list work

Record your participation in Piazza clicker question Lesson15 Q2

• Replace the element at index 2 with "marigold" (Use the set method)
• Print the size of the array list
• Print the last element in the ArrayList
• Replace the last element with "zinnia" (Do not use a magic number)
• Swap the the first two elements.

  get the element at index 0 and assign it to a variable named temp
  get the element at index 1 and set it in index 0
  set temp in index 1

• Print it. Did you get this?

  [rose, petunia, marigold, daisy, zinnia]

• Remove the element at 2 and add it at the end
• Note: The remove method violates the rule that says a method should not be both a mutator and an accessor. It returns the object that is removed
• Print it: You should get

  [rose, petunia, daisy, zinnia, marigold]

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]
• Print using the enhanced for loop

  for (String p: professors)
  {
      System.out.println(p);
  }

• Output:

  Heller
  O'Brien
  Wesley
  Stamp

Activity - ArrayLists and for loops

Record your participation in Piazza clicker question Lesson15 Q3

Using garden:

• Print each element on a separate line using a regular for loop
• Print each element on a separate line using an enhanced for loop

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 - More ArrayList

Record your participation in Piazza clicker question Lesson15 Q4

• Replace each element so it start with an uppercase letter
• You need to use a traditional for loop since you are changing the ArrayList
• pseudocode

  for each element in the ArrayList
     get the first letter of the string
     change the first letter to uppercase
     concatenate the uppercase letter with the rest of the word. 
     set the element back in the ArrayList

• Print the array list on one line

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