CS445 Recitation 7:25pm8:15pm

1
CS445 Recitation725pm-815pm

• Jan. 23 25, 2007 (T,H)

2
The Helpdesk Hours located in the 5712 lab
3
Homework 1

• Go over solution of homework 1
• (new Date()).getTime() number of ms since
  January 1, 1970, 000000 GMT
• Running Time
• Linear search 106 (around 220) comparisons
• Binary search log 220 20 comparisons

4
Generic Types

• If the data fields of a class can be objects of
  any class type, you can use a generic type when
  declaring them
• puclic class MyClassltTgt
• The identifier T can be any identifier
• MyClassltStringgt item new MyClassltStringgt()
• MyClassltIntegergt item new MyClassltIntegergt()
• Define more than one generic type with a class
  definition
• puclic class MyClassltT, S, Rgt

5
Generic Types within an Interface

• public interface PairableltSgt
• public void setPair(S firstItem, S lastItem)
• A class that implements this interface
• public class OrderedPairltTgt implements
  PairableltTgt
• public class Circle implements ComparableltCirclegt,
  Measurable

6
Generic Types

• Avoid casting

Object o Box b (Box)o//casting public
interface ComparableltTgt public int
compareTo(T) //casting is NOT needed in method
body public interface Comparable public
int compareTo(Object o) //casting is needed in
method body
7
ADT List

• Data
• A collection of objects in a specific order and
  having the same data type
• The number of objects in the collection
• Operations
• add(newEntry) at the end
• add(newPosition, newEntry) anywhere
• remove(givenPosition)
• clear() -- remove all
• replace(givenPosition, newEntry)
• getEntry(givenPosition)--look at
• contains(anEntry)
• getLength() -- count
• isEmpty() -- empty
• isFull() -- full
• display() -- display all the entries

8
Implementing ADT List

• Using fixed-size Array
• add(newEntry) at the end
• add(newPosition, newEntry) anywhere
• remove(givenPosition)
• clear() -- remove all
• replace(givenPosition, newEntry)
• getEntry(givenPosition)--look at
• contains(anEntry)
• getLength() -- count
• isEmpty() -- empty
• isFull() -- full

9
Implementing ADT List

• Using Array Expansion
• When an array is full, move its contents to a
  larger arraythe dynamic expansion of an array.
• isFull() always return false

int myArray new int100 //myArray is full,
expand it. int oldArray myArray myArray
new int2 oldArray.length for (int index0
index lt oldArray.length index)
myArrayindex oldArrayindex
Original array
Larger array
10
ArrayList A Java Class Library class that use
dynamic array expansion
 
 
Each Expansion increase the room by 50.
11
 
12
 
13
Why ArrayList ?

• Support generic type.
• Provide sorting and searching support for any
  ArrayList of objects that implement Comparable
  interface.

14
Java Classes Implementing Comparable
15
Examples

• http//www.cs.pitt.edu/aronis/cs445/misc/
  DemonstrateArrayList.java
• //////////////////////////////////////////////////
  ////////////////////
• /// Contents Demonstrate some capabilities of a
  generic ArrayList
• /// Author John Aronis
• //////////////////////////////////////////////////
  ////////////////////
• /// Java's ArrayList is a flexible, fast, and
  extremely useful data structure. It comes in two
  forms generic and vanilla. The generic form is
• /// illustrated below. A few of the most useful
  methods are illustrated see a good manual for
  many more.
• import java.util.ArrayList
• import java.util.Collections
• public class DemonstrateArrayList
• public static void main(String args)
• /// Create an ArrayList of Strings and fill
  it
• ArrayListltStringgt A new ArrayListltStringgt()
  
• A.add("d") A.add("b") A.add("e")
  A.add("a")
• A.add("h") A.add("f") A.add("c")
  A.add("g")
• System.out.println(A)
• /// Zip through it quickly
• for (int i0 iltA.size() i)
  System.out.print( A.get(i) " " )

Output d, b, e, a, h, f, c, g d b e a h f c
g a, b, c, d, e, f, g, h 2 -9 a, hello, foo,
c, e, f, g, h
16
Examples

• ArrayListltIntegergt B new ArrayListltIntegergt()
• B.add(6) B.add(2) B.add(4) B.add(9)
• B.add(1) B.add(8) B.add(9)
• System.out.println(B)
• /// Zip through it quickly
• for (int i 0 i lt B.size() i)
  System.out.print(B.get(i) " ")
• System.out.println()
• /// String implements Comparable, so sort it
  with Java's Quicksort
• Collections.sort(B)
• System.out.println(B)
• /// Search it with Java's binary search
• System.out.println(Collections.binarySearch(B,
  6))
• System.out.println(Collections.binarySearch(B,
  100))
• /// Demonstrate a few other important methods
• B.add(2, 33)

Output 6, 2, 4, 9, 1, 8, 9 6 2 4 9 1 8 9
1, 2, 4, 6, 8, 9, 9 3 -8 1, 111, 33, 4, 8, 9,
9
17
Examples

• public class CBox implements ComparableltCBoxgt
• public static int numberOfBoxes 0
• private float side 0.0F
• public CBox(float s)
• side s
• numberOfBoxes
• public float getSide() return side
• public void setSide(float s) side s
• public CBox add(CBox b)
• CBox result new CBox(0.0F)
• result.setSide( this.side b.side )
• return result
• public boolean equals(CBox b)
• return (this.side b.side)

18
Examples

• ArrayListltCBoxgt C new ArrayListltCBoxgt()
• C.add(new CBox(6)) C.add(new CBox(2)) C.add(new
  CBox(4)) C.add(new CBox(9))
• C.add(new CBox(1)) C.add(new CBox(8)) C.add(new
  CBox(9))
• System.out.println(C)
• /// Zip through it quickly
• for (int i 0 i lt C.size() i)
  System.out.print(C.get(i) " ")
• System.out.println()
• /// String implements Comparable, so sort it with
  Java's Quicksort
• Collections.sort(C)
• System.out.println(C)
• /// Search it with Java's binary search
• System.out.println(Collections.binarySearch(C,
  new CBox(6)))
• System.out.println(Collections.binarySearch(C,
  new CBox(100)))
• /// Demonstrate a few other important methods
• C.add(2, new CBox(222))

Output 6.0, 2.0, 4.0, 9.0, 1.0,
8.0, 9.0 6.0 2.0 4.0 9.0 1.0 8.0
9.0 1.0, 2.0, 4.0, 6.0, 8.0,
9.0, 9.0 3 -8 1.0, 111.0, 222.0,
4.0, 6.0, 8.0, 9.0, 9.0
Question When invoking the boolean
remove(Object o) method that is inherited from
List class, if C.remove(new CBox(8)) can remove
item from the right array list ?
19

• /////
• ///// Contents Demonstrate how to extract
  number from string.
• ///// Author John Aronis
• ///// Date January 2007
• /////
• public class TestStringForNumber
• public static void main(String args)
• String s
• s "foo"
• System.out.println("\nString\""s"\" ---")
• if ( isNumber(s) ) System.out.println(
  getNumber(s) )
• else System.out.println( "Can't fool me, that
  isn't a number!" )
• s "1.2345"
• System.out.println("\nString\"" s "\"
  ---")
• if (isNumber(s)) System.out.println(getNumber(s))
  
• else System.out.println( "Can't fool me, that
  isn't a number!" )
• System.out.println()

Output String"foo" --- Can't fool me, that
isn't a number! String"1.2345" --- 1.2345
20
ArrayList

• http//java.sun.com/j2se/1.4.2/docs/api/java/util/
  ArrayList.html
• http//java.sun.com/j2se/1.4.2/docs/api/java/util/
  Collections.html