Transcript Chapter 10 - Arraylist Unit 6 - chapter 10 arraylist_2

ARRAYLIST..
Hazen High School
Vocabulary to Know
• ArrayList
• Generic Class
• ArrayList Operations
• ArrayList Methods
• ArrayList Searching
• For-Each
• Wrapper Class
• Boxing
• Unboxing
• Comparable
• Comparison function
• Natural Ordering
What ?
• Resizable Array [Automatic]
• Allows Duplication.
• Order - Maintains Insertion order.
• Type Safety
• Capacity and Size
Array List
• The ArrayList class extends AbstractList and implements
the List interface.
• ArrayList supports dynamic arrays that can grow as
needed.
• In Java, standard arrays are of a fixed length. After arrays
are created, they cannot grow or shrink, which means that
you must know in advance how many elements an array
will hold
Array Lists
• an ArrayList can dynamically increase or decrease in size.
• Array lists are created with an initial size.
• When this size is exceeded, the collection is automatically
enlarged.
• When objects are removed, the array may be shrunk
Methods and Fields
• ArrayList list = new ArrayList()
• Assignment / Insertion
• list.Add(“Item1”); // Syntax : list.add(<Object>)
• Size :
• int arrayListLength = list.Size();
• Retrieval :
• String firstString = list.get(0); // Syntax : list.get(<Index>)
• Removal :
• list.Remove(0) // Syntax : list.Remove(<Index>)
• Others
• IsEmpty(), Clear(), ToArray(), Set(Index, Object)
• See full reference list at end of the slide deck.
Generics - Type Parameters
ArrayList<Type> name = new ArrayList<Type>();
•—
When constructing an ArrayList, you must specify the type
of elements it will contain between < and >.
• —
This is called a type parameter or a generic class.
• —
Allows the same ArrayList class to store lists of different
types.
•ArrayList<String> names = new ArrayList<String>();
•names.add(“Kory Srock”); names.add(“Tod
Oney”);
Generics
• Using different classes in Collection.
• Why ?
• Better programmability
• Better Object Orientation
• Example
• ArrayList myList = new ArrayList();
• ArrayList<int > a = new ArrayList<int >()
• ArrayList<Vehicle> list = new ArrayList<Vehicle >()
Array Vs ArrayList
• Grows automatically
• Work well with Generics
• ArrayList<String> stringArrayList = new ArrayList<String>();
• ArrayList<MyClass> stringArrayList = new ArrayList<MyClass>();
• Objects vs References
• Pass by Value --- Pass by Reference
ArrayList of primitives?
• The type you specify when creating an ArrayList must be
an object type; it cannot be a primitive type.
// illegal -- int cannot be a type parameter
ArrayList<int> list = new ArrayList<int>();
• But we can still use ArrayList with primitive types by using
special classes called wrapper classes in their place.
// creates a list of ints
ArrayList<Integer> list = new ArrayList<Integer>();
Wrapper classes
 A wrapper is an object whose sole
purpose is to hold a primitive
value.
 Once you construct the list, use it
with primitives as normal:
Primitive
Wrapper
intType
IntegerType
double
Double
char
Character
boolean
Boolean
ArrayList<Double> grades = new ArrayList<Double>();
grades.add(3.2); grades.add(2.7);
... double myGrade = grades.get(0
ArrayList versus Array – Code Examples
• Construction
String[] names = new String[5];
ArrayList<String> list = new ArrayList<String>();
• Storing a value
names[0] = "Michael";
list.add("Michael");
• Retrieving a value
String s = names[0];
String s = list.get(0);
ArrayList vs Array – Code Examples Continued
• Doing something to each value that starts with "B"
for (int i = 0; i < names.length; i++) {
if (names[i].startsWith("B")) { ... }}
for (int i = 0; i < list.size(); i++) {
if (list.get(i).startsWith("B")) { ... } }
• Seeing whether the value "Nathaniel" is found
for (int i = 0; i < names.length; i++) {
if (names[i].equals("Nathaniel")) { ... }}
if (list.contains("Nathaniel")) { ... }
Objects storing collections
• An object can have an array, list, or other collection as a
field.
public class Course {
private double[] grades;
private ArrayList<String> studentNames;
public Course() {
grades = new double[4];
studentNames = new ArrayList<String>();
...
}
• Now each object stores a collection of data inside it.
• This is called “composition” (the collection is a
component)
Exercise #1
• Write a method addStars that accepts an array list of
strings as a parameter and places a * after each element.
—
Example: if an array list named list initially stores:
[the, quick, brown, fox]
—
Then the call of addStars(list); makes it store:
[the, *, quick, *, brown, *, fox, *]
• Write a method removeStars that accepts an array list of
strings, assuming that every other element is a *, and
removes the stars (undoing what was done by addStars
above).
Questions
ArrayList list = new ArrayList()
list.Add(“Item1”);
list.Add(“Item1”);
list.Add(“Item2”);
Will this compile ?
Yes, assuming declaration of
import java.util.ArrayList;
Questions.. Cntd..
• ArrayList list = new ArrayList()
• list.Add(“1”);
• list.Add(“2”);
• list.Add(3);
Yes, all are added as objects
Will this compile ?
Questions.. Cntd..
• ArrayList list = new ArrayList(3)
• list.Add(“1”);
• list.Add(“2”);
• list.Add(“3”);
• list.Add(“4”);
Will this compile ?
Yes. ArrayList grows dynamically
Questions.. Cntd..
• ArrayList list = new ArrayList(4)
• list.Add(“1”);
• list.Add(“2”);
• list.Add(“2”);
Yes, it will compile
• list.Add(“4”);
• System.out.println(list.indexOf(“2”));
Will this compile ?
Output ?
Output is 1
Questions.. Cntd..
• ArrayList list = new ArrayList(4);
• list.add(“1”);
• list.add(“2”);
What do we need to do to fix it?
• list.add(“2”);
• list.add(“4”);
Change for loop to 4 instead of 5
• for(int i=0;i<5;i++)
• System.out.println(list.get(i));
Will this compile ?
Output ?
No, IndexOutOfBoundsException
Question .. Tricky
ArrayList arr1 = new ArrayList();
No, there is no method .length for arraylists,
ArrayList arr2 = arr1;
need to use .size
arr1.Add("Test");
System.out.println(arr1.Length == arr2.Length);
Compile?
Output ?
What is the output once we change .length to .size?
true
ArrayList arr1 = new ArrayList();
ArrayList arr2 = new ArrayList();
arr1.Add("Test");
Won’t compile – arr1[0]= “Test1” is a array type conflict
arr2.Add(arr1.get(0));
arr1[0] = “Test1”;
What do we need to do to fix it?
System.out.println(arr2.get(0));
Arr1.add(“Test1”)
Compile?
Output ?
import java.util.*;
class ArrayListDemo {
What is the initial size of al?
public static void main(String args[]) {
ArrayList al = new ArrayList(); // create an array list
System.out.println("Initial size of al: " + al.size());
Initial size of al: 0
// add elements to the array list
al.add("C");
al.add("A");
al.add("E");
What is the size of al after additions?
al.add("B");
al.add("D");
al.add("F");
Size of al after additions: 7
al.add(1, "A2");
What is the contents of al?
System.out.println("Size of al after additions: " +al.size());
// display the array list
System.out.println("Contents of al: " + al);
Contents of al: [C, A2, A, E, B, D, F]
// Remove elements from the array list al.remove("F");
al.remove(2);
What is the size after deletions?
System.out.println("Size of al after deletions: " + al.size());
System.out.println("Contents of al: " + al);
Size of al after deletions: 5
}
}
Contents of al: [C, A2, E, B, D]
Exercise #2
• Use Array List to implement the following exercise
• Create and Display a List of Employees in a Company with each Employee
information containing the following
• Id
• Name
• Date of Birth
• Designation
• Address
• Skill Sets [ Accounts, Sales, Marketing, IT, Support, Management, Delivery ]
• List of products worked [ ProjectX, PriojectY, ProjectZ, ProjectH ]
• Each Project should track the list of Employees in it
• Each Dept./Skill Sets should track the list of Employees in it
• Hint :
• Use Static variables to track the List of Employees and Count of them in Project / Department
Array List Methods
add(value)
appends value at end of list
add(index, value)
inserts given value just before the given index,
shifting subsequent values to the
rightremoves all elements of the list
clear()
indexOf(value)
returns first index where given value is found in
list (-1 if not found)
get(index)
returns the value at given index
remove(index)
removes/returns value at given index, shifting
subsequent values to the left
set(index, value)
replaces value at given index with given
valuereturns the number of elements in list
size()
toString()
returns a string representation of the list such
as "[3, 42, -7, 15]"
Array List Methods Continued
addAll(list) addAll(index, list)
adds all elements from the given list to this list (at the end of the list, or
inserts them at the given
contains(value)
index)returns true if given value is found somewhere in
containsAll(list)
this listreturns true if this list contains every element from
equals(list)
given listreturns true if given other list contains the same
iterator() listIterator()
elementsreturns an object used to examine the contents of the list (seen later)
lastIndexOf(value)
returns last index value is found in list (-1 if not
remove(value)
found)finds and removes the given value from this list
removeAll(list)
removes any elements found in the given list from
retainAll(list)
this listremoves any elements not found in given list from
subList(from, to)
this listreturns the sub-portion of the list between indexes from (inclusive) and
to (exclusive)
toArray()
returns the elements in this list as an array
PracticeIt
• http://www.garfieldcs.com/2011/02/arraylists-practice/
• http://practiceit.cs.washington.edu/problem.jsp?category=
University+of+Washington+CSE+143%2FCS2+Exams%2
FCS2+Midterm+Exams%2F143+Practice+Midterm+5&pro
blem=143practicemidterm5-ArrayListMystery
• http://www.garfieldcs.com/2011/03/classes-quiz-practice/
Question .. Tricky
ArrayList arr1 = new ArrayList();
ArrayList arr2 = arr1.clone();
arr1.Add("Test");
arr2.Add(arr1.get(0));
arr1[0] = “Test1”;
System.Out.PrintLn(arr2.get(0));
Output ?
ArrayList arr1 = new ArrayList();
ArrayList arr2 = new ArrayList();
arr1.Add("Test");
arr2.Add(arr1.get(0).Clone());
arr1[0] = “Test1”;
System.Out.PrintLn(arr2.get(0));
Output ?