Class Object

1
Class Object

• Common parent (base class)
• Minimal functionality
• Classes may override to provide specific
  behaviour
• public boolean equals(Object other)
• public int hashCode()
• public String toString()
• public Class getClass()
• public Object clone()

2
Serialization

• Serialization is the process of transforming an
  object into a stream of bytes.
• Deserialization is the reverse process.
• public interface Serializable
• Making an object serializable requires almost no
  effort (the interface Serializable is empty).
• More complex operations may be necessary if, for
  instance, just a portion of an objects state is
  to be saved on the output stream.

3
Serialization (cont.)

• import java.io.
• public class IntPair implements Serializable
• int x
• int y
• public IntPair(int x, int y)
• this.x x
• this.y y
• public String toString()
• return (" x "," y ")"

4
Serialization (cont.)

• import java.io.
• public class inout
• public static void main(String args)
• IntPair p new IntPair(2,3)
• try
• ObjectOutputStream out new
  ObjectOutputStream(
• new FileOutputStream(Filename))
• out.writeObject(p)
• out.close()
• catch(IOException e)
• e.printStackTrace()

5
Serialization (cont.)

• import java.io.
• public class inout
• public static void main(String args)
• try
• ObjectInputStream in new
  ObjectInputStream(
• new FileInputStream(Filename))
• IntPair p (IntPair) in.readObject()
• System.out.println(p)
• catch(Exception e)
• e.printStackTrace()

6
Some useful interfaces

• interface Serializable
• interface Cloneable
• this interface does not include the clone method.
• a class implements the Cloneable interface to
  indicate to the Object.clone() method that it is
  legal for that method to make a field-for-field
  copy of instances of that class.
• interface ComparableltTgt
• public int compareTo(T o)
• this interface imposes a total ordering on the
  objects of each class that implements it.
• compareTo(T o) returns a negative integer, zero,
  or a positive integer as this object is less
  than, equal to, or greater than the specified
  object.
• interface ComparatorltTgt
• public int compare(T o1, T o2)

7
Utility Classes

• The Java library provides a number of small
  utility classes, including
• Point
• Dimension
• Date, Calendar
• Math
• Random
• Toolkit
• System
• String and related classes

8
Points
x
Points represent locations in a two-dimensional
space.
y

• class Point implements Cloneable, Serializable
• public Point(int x, int y) //constructor
• public int x //public accessible data
• public int y //fields
• public void move(int x, int y) //move to a
  given location
• public void translate(int x, int y) //change by
  offset
• public boolean equals(Object p) //compare two
  points
• public String toString() //convert to string

9
Dimension

• A dimension is used to represent a rectangular
  size. Dimensions are
• characterized by a width and a height.
• class Dimension implements Cloneable,
  Serializable
• public Dimension() //constructors
• public Dimension(int w, int h)
• public Dimension(Dimension d) //make a copy
  (clone ?!?!)
• public int width //public accessible data
  fields
• public int height
• public String toString() //operations

10
Date, Calendar

• The class Date is used to represent both data and
  time values.
• class Date implements Cloneable, Comparable,
  Serializable
• public Date() //constructors
• public Date(int year, int month, int
  day) //deprecated,
• public Date(int year, int month, int day,
  //replaced by
• int hours, int minutes) //Calendar and
• public Date(int year, int month, int day, //the
  set method int hours, int minutes, int seconds)
• public int getDate() //field access methods
• public int getDay() //deprecated, replaced by
  Calendar and the
• public int getHours() //get method
• public int getMinutes()
• public int getMonth()
• public int getSeconds()
• public int getYear()
• public int getTimezoneOffset()

11

• //epoch methods
• public long getTime() //returns milliseconds
  since epoch
• public void setTime(long lval) //set time from
  epoch
• //field setting methods
• public void setDate(int date) //deprecated,
  replaced by
• public void setHours(int hour) //Calendar and
  the get method
• public void setMinutes(int minutes)
• public void setMonth(int month)
• public void setSeconds(int seconds)
• public void setYear(int year)
• //comparison methods
• public boolean after(Date when)
• public boolean before(Date when)
• public boolean equals(Object when)
• //output
• public String toString()

12
Date - Example

• Date start new Date()
• int j 0
• for (int i 0 i lt 100000 i)
• j j 1
• Date end new Date()
• System.out.println(That took
• (end.getTime() start.getTime())
• milliseconds. )

13
Math

• The class Math provides a number of constants, as
  well as useful
• mathematical functions.
• final class Math
• //constants
• public static final double E //2.71828
• public static final double PI //3.14159
• //trigonometric operations, angles in radians
• public static double sin(double num)
• public static double cos(double num)
• public static double tan(double num)
• public static double asin(double num)
• public static double acos(double num)
• public static double atan(double num)
• public static double atan(double s, double c)

14

• //rounding operations
• public static double ceil(double num)
• public static double floor(double num)
• public static double rint(double num)
• public static int round(float num)
• public static long round(double num)
• //exponential and powers
• public static double exp(double y)
• public static double pow(double x, double y)
• public static double log(double x)
• public static double sqrt(double x)

15

• //other operations
• public static int abs(int num)
• public static long abs(long num)
• public static float abs(float num)
• public static double abs(double num)
• public static int max(int x, int y)
• public static long max(long x, long y)
• public static float max(float x, float y)
• public static double max(double x, double y)
• public static int min(int x, int y)
• public static long min(long x, long y)
• public static float min(float x, float y)
• public static double min(double x, double y)
• public static double random()

16
Random

• The class Random provides more general facilities
  for random numbers.
• class Random implements Serializable
• //constructors
• Random()
• Random(long seed)
• //operations
• public void setSeed(long seed)
• public double nextDouble()
• public float nextFloat()
• public int nextInt()
• public int nextInt(int n)
• public long nextLong()
• //alternative distribution
• public double nextGaussian()

17
Random - Example

• static public int weightedDistribution(int
  weights)
• int sum 0
• for(int i 0 i lt weights.length i)
• sum weightsi
• int val (int) Math.floor(Math.random()sum
  1)
• for(int i 0 i lt weights.length i)
• val - weightsi
• if (val lt 0) return i
• return 0

18
Toolkit

• This class is the abstract superclass of all
  actual implementations of the Abstract Window
  Toolkit (AWT).
• Useful methods
• getFontList() returns an array of string values,
  containing the names of the fonts available on
  the current system.
• getImage() takes as a parameter either a string
  (a file name) or a URL returns an image as a
  value of type Image.
• getScreenSize() returns the number of pixels
  (type Dimension) in the screen.
• getScreenResolution() returns the number of dots
  per inch.
• The Toolkit class is an example of the Abstract
  Factory design pattern .

19
System

• The class System gives access to several
  system-wide resources.
• System.in standard input
• System.out standard output
• System.err error output
• Useful methods
• exit(int) immediately halts the current running
  program, yielding to the operating system the
  integer status given in the argument.
• currentTimeMillis() returns the current time in
  milliseconds since epoch.

20
String

• In Java a string is an immutable object it
  cannot be changed.
• implements CharSequence, Comparable, Serializable
• String name John Smith
• The addition operator, , is overloaded
• System.out.println(The answer is answer)
• addition operator groups left to right, i.e.,
• System.out.println(Catch- 2 2)
• yields Catch-22,
• System.out.println(2 2 warned)
• yields 4warned
• use equals(Object obj) or equalsIgnoreCase(String
  str) to compare strings

21
String (cont.)

• final class String
• ?
• public static String valueOf(Object obj)
• if (obj null)
• return null
• else
• return obj.toString()
• ?
• If obj is a string valueOf returns a reference to
  the original, not a copy!

22
StringBuffer

• String as an array of character symbol similar
  to C.
• The methods append, insert, and reverse change
  the current string buffer and return a reference
  to the updated string buffer.
• String str1 Hello
• String str2 str1 str1
• StringBuffer strbuf1 new StringBuffer(Hello
  )
• StringBuffer strbuf2 strbuf1.append(strbuf1)

23
Collections

• containers, data structures
• kinds
• bags (multiset)
• unordered with duplicates
• Collection
• set
• unordered without duplicates
• also sorted or ordered sets
• Set and SortedSet
• list (sequence)
• ordered with duplicates
• indexing by position
• List
• map (dictionary, associative array)
• unordered (key,value) pairs
• no duplicate keys
• map from key to value
• also sorted or ordered map (by key)
• Map and SortedMap

24
Interfaces

• design guideline Maximize the Uniformity of
  Common Aspects of Related Classes/Interfaces

E
Iterable
E
K,V
Collection
Map
E
E
K,V
Set
List
SortedMap
E
SortedSet
25
Interfaces

• Iterable
• iterator
• Collection
• common interface for non-map collections
• equals
• Set
• modifies semantics no duplicates
• SortedSet
• List
• modified semantics ordered
• Map
• not Collection involves keys, no duplicate keys
• views
• entry set (key-value pairs)
• key set
• value collection
• keys
• equals
• SortedMap

26
CollectionltEgt interface
27
SetltEgt interface
28
ListltEgt interface
29
ListltEgt interface (cont.)
30
SortedSetltEgt interface
31
MapltK,Vgt interface
32
SortedMapltK,Vgt interface
33
Concrete Classes

• Important issues
• bounded versus unbounded
• time and space complexity of various operations
• interchangeability
• concrete collection classes in Java
• all unbounded

34
SetltEgt

• HashSetltEgt
• hash table (efficient in insertion and membership
  checking)
• unpredictable iteration order
• requires equals and hashCode
• LinkedHashSetltEgt (similar to HashSet)
• hash table with linked elements
• predictable iteration order (usually insertion
  order)
• requires equals and hashCode
• TreeSetltEgt
• red-black tree (a form of balanced binary trees)
• SortedSet
• requires ordering (Comparable or Comparator)
• iteration by natural order
• less efficient in insertion and membership
  checking
• Use HashSet unless a sorted set or a predictable
  iteration order is required.

35
ListltEgt

• ArrayListltEgt
• array extended when necessary
• large enough to hold predicted number of elements
• often, a large portion of the array is unused
• large cost to increase size (copying)
• more efficient access
• VectorltEgt
• same implementation as the ArrayList
• supports additional legacy methods
• thread-safe
• significant overhead in performance
• LinkedListltEgt
• doubly-linked list
• no additional penalty as list grows
• less efficient access
• LinkedList for volatile lists, ArrayList for
  stable lists

36
MapltK,Vgt

• HashMapltK,Vgt
• hash table (efficient in insertion and membership
  checking)
• unpredictable iteration order
• requires equals and hashCode
• HashtableltK,Vgt
• same implementation as the HashMap
• supports additional legacy methods
• thread-safe
• significant overhead in performance
• LinkedHashMapltK,Vgt
• hash table with linked elements
• predictable iteration order (usually insertion
  order)
• requires equals and hashCode

37

• IdentityHashMapltK,Vgt (similar to HashMap)
• key equality based on (identity)
• requires hashCode
• TreeMapltK,Vgt
• red-black tree
• SortedMap
• iteration order by key
• requires ordering for keys (Comparable or
  Comparator)
• less efficient in insertion and membership
  checking
• Use TreeMap if a sorted map is required otherwise
  use HashMap or IdentityHashMap.

38
Abstract Collection Classes

• for building new collections
• AbstractCollectionltEgt
• bag
• must implement iterator and size
• AbstractSetltEgt
• must implement add
• AbstractListltEgt
• optimized for random access
• must implement get and size
• AbstractSequentialListltEgt
• optimized for sequential access
• must implement listIterator and size
• AbstractMapltK,Vgt
• must implement entries