1. ArrayList
Collections

2. How Do I Use an ArrayList?
First, import it so it is available for use:
import java.util.ArrayList;
-or-
import java.util.*;

3. How Do I Use an ArrayList?
Next declare and initialize!
ArrayList<Point> myPoints;
myPoints = new ArrayList<Point>();
//note: The initial capacity of an ArrayList is 10
Recall the Java array style
Point[] myPoints;
myPoints = new Points[10];

4. How do I add items?
Call the add method (adds the item to the back of the ArrayList).
Point p = new Point(1,2);
myPoints.add(p);
myPoints.add(new Point(2,3));

5. How many items are in the ArrayList?
For an ArrayList, we use
myPoints.size()
For an array, we use
myPointsArr.length
Note: size() gives number of items, length gives the capacity

6. How do I retrieve items? For an ArrayList For an array,
Point p = myPoints.get(0);
For an array,
Point p = myPointArr[0];

7. Example (Traversal and set)
Given an ArrayList called myNames filled with names, replace all occurrences of “marc” with “mark”.
for(int i = 0; i < myNames.size(); i++) {
if (myNames.get(i).equals(“marc”))
myNames.set(i, “mark”); }
Note: The set method replaces what is at i with the new element and returns the old element (which is ignored in this case).

8. Traversal with “for each” loop
for(String s: myNames) {
if (myNames.get(i).equals(“marc”))
myNames.set(i, “mark”); }

9. Can elements only be added at the back of the ArrayList?
No! You can add an element at any valid index.
Consider the ArrayList named myAlphabet:
[“apple”, “bear”, “cake”, “dog”]
The call
myAlphabet.add(2, “zebra”);
results in
[“apple”,“bear”,“zebra”,“cake”,“dog”]
Note: No need to shift things over by hand! ArrayList does this for you!!!

10. Special note on add Given the following ArrayList named myAlphabet:
[“apple”, “bear”, “cake”, “dog”]
The following two calls would produce identical results:
myAlphabet.add(“zebra”)
myAlphabet.add(4, “zebra”);
Note: myAlphabet.add(5, “zebra”) will cause an IndexOutOfBoundsException.

11. Easy to remove as well! [“apple”, “bear”, “cake”, “dog”]
Remember the pain of removing with arrays (having to shift elements to the left). ArrayList does this for you!
Given
[“apple”,“bear”,“zebra”,“cake”,“dog”]
myAlphabet.remove(2) results in
[“apple”, “bear”, “cake”, “dog”]

12. Summary of ArrayList methods
class java.util.ArrayList<E>
int size()
boolean add(E e)
appends e to end of list, returns true
void add(int i, E e)
inserts e at index of i (0 <= i <= size) moving elements right as necessary
E get(int i)
returns element at index of i
E set(int i,E e)
replaces element at i with e, returns former element at i
E remove(int i)
removes element at I moving elements left as necessary.

13. Arrays vs. ArrayList Arrays ArrayList Declaration/Initialization
Point[] p;
p = new Point[5];
ArrayList<Point> p;
p=new
ArrayList<Point>();
Assignment (replace)
p[3]=aPoint;
p.set(3, aPoint);
Insertion
Lots of code to shift element right
p.add(2, aPoint);
Deletion
Lots of code to shift elements left
p.remove(2);
Number of items
p.length
p.size();
Access
p[4].getX();
p.get(4).getX();