Arrays

1
Arrays

• Arrays
• Collections (Set, Database, History)
• Inheritance
• inheriting ancestors traits
• inheriting benefactors assets
• inheriting instance members( methods/variables)
• IS-A Relationship
• human IS-A Mammal
• salmon IS-A Fish
• Joe Doe IS-A Student
• ALoan IS-A Loan

2
Strings Char Sequences
String
sequences of characters
3
Other Sequences as Predefined Types
sequences of integers
IntSequence
100
98
99
100
90
80
60
40
50
sequences of doubles
DoubleSequence
3.8
3.1
3.7
3.1
3.6
3.9
sequence of Strings
StringSequence
JFK
FDR
JC
BC
RR
GB
4
Sequences of Programmer-Defined Type
sequence of loans
LoanSequence
Loan
loan1
loan2
loan3
sequence of temperatures
TemperatureSequence
Temperature
5
Other Sequences as Array Types
sequences of integers
int
100
98
99
100
90
80
60
40
50
sequences of doubles
double
3.8
3.1
3.7
3.1
3.6
3.9
sequence of strings
String
JFK
FDR
JC
BC
RR
GB
6
Initializing Array Declarations
int assignmentScores 100, 98, 99, 80
assignmentScores
100
98
99
100
90
80
7
Initializing Array Declaration
ltElementTypegt ltarrayVariablegt ltelement1gt,
, ltelementNgt
Loan loans new ALoan(100000), new
AnotherLoan (100)
8
Array Operations
initials.length
? 6
Array Instance Size Fixed
initials0
initialsinitials.length - 1
initialsinitials.length
? ArrayIndexOutOfBoundsException
initials0 HT
initialsinitials.length HT
? ArrayIndexOutOfBoundsException
9
Array Types have Variable-Size
int
100
98
99
100
90
80
60
40
50
int assignmentScores 100, 98, 99, 100, 99,
80
assignmentScores 60, 40, 50
assignmentScores
100
98
99
100
90
80
10
Uninitializing Array Declaration
int assignmentScores
assignmentScores 60, 40, 50
null
11
Array Elements Uninitialized
int assignmentScores new int3
12
Object Array Elements Uninitialized
String initials new String3
13
Uninitialized Array Vs Element
String initials
initials0
? ArrayIndexOutOfBoundsException
String initials new String3
? null
initials0
initials0.charAt(0)
? StringIndexOutOfBounds
14
Example
15
getStrings()
static String getStrings()
System.out.println("Number of Strings")
int numElements Keyboard.readInt()
System.out.println("Please enter " numElements
" strings") String strings new
StringnumElements for (int elementNum
0 elementNum lt numElements elementNum)
stringselementNum Keyboard.readLine()
return strings
16
print()
static void print(String strings)
System.out.println("")
for ( int elementNum 0 elementNum lt
strings.length elementNum)
System.out.println(stringselementNum)
System.out.println("")
17
main()
public static void main(String args)
String names getStrings() while
(true) String command
Keyboard.readLine() if
(command.length gt 0 command.charAt(0)
'q') break if
(command.length gt 0 command.charAt(0)
'p') print(names)
18
main()
19
Variable-Size Collection
unfilled part
filled part
20
Variable-Size Collection
size
array
3
filled part
unfilled part
21
Variable-Size Collection
public class ltClassNeedingVariableSizeCollectiongt
final static int A_MAX_SIZE
50 String a new String MAX_SIZE int aSize
0 //process a for (int index 0 index lt
aSize index)
System.out.println(aindex) final int
B_MAX_SIZE 50 String b new String
MAX_SIZE int bSize 0 //process
b
22
Special Type
public class ltClassNeedingVariableSizeCollectiongt
... AVariableSizeCollection a new
AVariableSizeCollection() ... for (int
index 0 index lt a.size index)
System.out.println(a.contentsindex)
AVariableSizeCollection b new
AVariableSizeCollection() ...
a.contentsa.size Keyboard.readString()
public class AVariableSizeCollection public
static final int MAX_SIZE 50 public String
contents new String MAX_SIZE public int size
0
23
Supporting Encapsulation
public interface . public
static final int MAX_SIZE 50
public void addElement (String element)
public void print ()
24
History
public interface StringHistory
public void addElement (String element)
public int size()
public String elementAt (int index)
25
Implementing a History
public class AStringHistory implements
StringHistory public final int MAX_SIZE
50 String contents new
StringMAX_SIZE int size 0 public
int size() return size public String
elementAt (int index) return contentsindex
boolean isFull() return size MAX_SIZE
public void addElement(String element)
if (isFull()) System.out.println(
"Adding item to a full history") else
contentssize element
size
26
Using a History
public static void main(String args)
StringHistory names new AStringHistory()
while (true) String input
Keyboard.readLine() if (input.length gt 0)
if (input.charAt(0) 'q') break
else if (input.charAt(0) 'p' )
print(names)
else names.addElement(input)

27
Printing a History
static void print(StringHistory strings)
System.out.println("")
for ( int elementNum 0 elementNum lt
strings.size() elementNum) System.out.println
(strings.elementAt(elementNum))
28
Database
29
Database
public interface StringDatabase
//from history public int size() public void
addElement (String element) public String
elementAt (int index) //additional methods
public void deleteElement(String element)
public void member (String element)
public void clear()
30
deleteElement (String element)
deleteElement(Joe Doe)
size
array
public void deleteElement (String element)
contentsindexOf(element) contentssize -
1 size--
4
3
John Smith
John Smith
31
deleteElement (String element)
deleteElement(Joe Doe)
size
array
public void deleteElement (String element)
shiftUp(indexOf(element))
4
John Smith
32
Multi-element window
deleteElement(Joe Doe)
size
array
public void deleteElement (String element)
shiftUp(indexOf(element))
4
Jane Smith
John Smith
contentsindex contentsindex 1
33
deleteElement (String element)
deleteElement(Joe Doe)
size
array
public void deleteElement (String element)
shiftUp(indexOf(element))
4
3
Jane Smith
void shiftUp (int startIndex) for (int
index startIndex index 1 lt size index)
contentsindex contentsindex
1 size--
John Smith
John Smith
34
indexOf (String element)
indexOf(Joe Doe)
size
array
4
John Smith
35
indexOf (String element)
deleteElement(Joe Doe)
size
array
4
public int indexOf (String element) for
( index 0 index lt size
!element.equals(contentsindex
index)
return index
John Smith
36
public boolean member(String element)
member(Joe Doe)
size
array
public int indexOf (String element) for (
index 0 index lt size
!element.equals(contentsindex
index)
return index
4
John Smith
public boolean member (String element)

return indexOf (element) lt size
37
public void clear()
clear()
size
array
4
3
2
1
0
public void clear() while ( size gt 0)
deleteElement(size -1)
John Smith
38
public void clear()
clear()
size
array
4
public void clear() size 0
0
John Smith
39
addElement(Mary Doe)
size
array
4
1
John Smith
40
Logical but not Physical Extensions
41
Database
public interface StringDatabase
//from history public int size() public void
addElement (String element) public String
elementAt (int index) //additional methods
public void deleteElement(String element)
public void member (String element)
public void clear()
42
Physical and Logical Extensions
43
Extending an Interface
public interface StringDatabase extends
StringHistory
public void deleteElement(String element)
public void member (String element)
public void clear()
44
Extending a Class
public class AStringDatabase extends
AStringHistory implements StringDatabase
public void deleteElement (String element)
int indexOf (String element)
void shiftUp (int startIndex)
public boolean member(String element)
public void clear()
45
Physical and Computer Inheritance
AStringDatabase
Human
StringDatabase
Deluxe Accord
46
No Explicit Extension
public class AStringHistory implements
StringHistory public final int MAX_SIZE
50 String contents new
StringMAX_SIZE int size 0 public
int size() return size public String
elementAt (int index) return contentsindex
boolean isFull() return size MAX_SIZE
public void addElement(String element)
if (isFull()) System.out.println(
"Adding item to a full history") else
contentssize element
size
47
Equivalent Class Definition
public class AStringHistory extends Object
implements StringHistory public final int
MAX_SIZE 50 String contents new
StringMAX_SIZE int size 0 public
int size() return size public String
elementAt (int index) return contentsindex
boolean isFull() return size MAX_SIZE
public void addElement(String element)
if (isFull()) System.out.println(
"Adding item to a full history") else
contentssize element
size
48
Some Methods of Class Object
toString( )
size
size( )
EXTENDS
AString History
Object
contents
elementAt( )
equals( )
MAX_SIZE
addElement( )
clone( )
isFull( )
(new AStringHistory()).toString()
EXTENDS
(new AStringDatabase()).toString()
member( )
AString Database
(new ALoan()).toString()
deleteElement( )
hello.toString()
indexOf( )
h.toString()
shiftUp( )
clear( )
5.toString()
49
IS-A Relationships
Object
StringHistory
AStringHistory
String
AStringDatabase
StringDatabase
implements
extends
50
IS-A Polymorphism
public static Loan add(Loan loan1, Loan loan2)
return new ALoan(loan1.getPrincipal()
loan2.getPrincipal()))
IS-A
51
Printing a History
static void print(StringHistory strings)
System.out.println("")
for ( int elementNum 0 elementNum lt
strings.size() elementNum) System.out.println
(strings.elementAt(elementNum))
AStringHistory IS-A StringHistory
AStringDatabase IS-A AStringHistory
AStringDatabase IS-A StringHistory
52
Assignment Rules for Primitive Types

• If T1 narrower than T2 (Set of instances of T1 ?
  Set of instances of T2)
• Expression of type T1 can be assigned to Variable
  of type T2
• Expression of type T2 can be assigned to Variable
  of type T1 with cast.

53
Assignment Rules for Object Types

• If T1 IS-A T2
• Expression of type T1 can be assigned to Variable
  of type T2
• Expression of type T2 can be assigned to Variable
  of type T1 with cast.

54
IS-A Definition

• Implements T1 implements T2 gt T1 IS-A T2
• Extends T1 extends T2 gt T1 IS-A T2
• Transitive
• T1 IS-A T2
• T2 IS-A T3
• gt T1 IS-A T3
• Reflexive
• T1 T2 gt T1 IS-A T2

55
Type Checking Examples
StringHistory stringHistory new
AStringDatabase()
StringDatabase stringDatabase new
AStringHistory()
56
Getting an Upgrade
ARegularModel myCar new ADeluxeModel ()
57
Getting a Downgrade
ADeluxeModel myCar new ARegularModel ()
58
Type Checking Examples
StringHistory stringHistory new
AStringDatabase()
stringHistory.size()
stringHistory .clear()
((StringDatabase) stringHistory) .clear()
StringDatabase stringDatabase new
AStringHistory()
stringDatabase.clear()
59
Type Checking Examples
Object objects Joe Doe, new
AStringDatabase(), new AStringHistory()
String strings Joe Doe, new Object()
60
Database
61
Set
62
Overriding Inherited Methods
toString( )
size
size( )
EXTENDS
AString History
Object
contents
elementAt( )
equals( )
MAX_SIZE
addElement( )
clone( )
isFull( )
EXTENDS
member( )
AString Database
addElement( )
deleteElement( )
indexOf( )
shiftUp( )
clear( )
63
Overriding addElement()
public void addElement(String element)
if (isFull()) System.out.println("Addi
ng item to a full history") else
contentssize element
size
public void addElement(String element)
if (member(element)) return if
(isFull()) System.out.println("Adding
item to a full history") else
contentssize element
size
64
super
public void addElement(String element)
if (isFull()) System.out.println("Addi
ng item to a full history") else
contentssize element
size
public void addElement(String element)
if (member(element)) return
super.addElement()
65
Omitting Super
public void addElement(String element)
if (isFull()) System.out.println("Addi
ng item to a full history") else
contentssize element
size
public void addElement(String element)
if (member(element)) return
addElement()
66
More Overriding
toString( )
size
size( )
EXTENDS
AString History
Object
contents
elementAt( )
equals( )
MAX_SIZE
addElement( )
clone( )
isFull( )
EXTENDS
member( )
AString Database
addElement( )
deleteElement( )
indexOf( )
shiftUp( )
clear( )
toString( )
67
More Overriding
stringSet.toString()
? AStringSet_at_1eed58
public String toString() String retVal
for (int i 0 i lt size i) retVal
contentsi return retVal
stringSet.toString()
? James DeanJohn Smith
68
Motivation for Switch
public static void main(String args)
StringDatabase names new AStringDatabase()
while (true) String input
Keyboard.readLine() if
(!(input.length() 0)) if
(input.charAt(0) 'q') break
else if (input.charAt(0) 'p')
print(names) else if
(input.charAt(0) 'd')
names.deleteElement(input.substring(2,
input.length())) else if
(input.charAt(0) 'm')
System.out.println(names.member(input.substring(2,
input.length()))) else if
(input.charAt(0) 'c')
names.clear() else
names.addElement(input)
69
Main with Switch
public static void main(String args)
StringDatabase names new AStringDatabase()
while (true) String input
Keyboard.readLine() if
(!(input.length() 0)) if
(input.charAt(0) 'q') break else switch
(input.charAt(0)) case 'p'
print(names) break case 'd'
names.deleteElement(input.substring(2,
input.length())) break case 'm'
System.out.println(names.member(input.substri
ng(2, input.length()))) break case
'c' names.clear() break
default names.addElement(input)

70
Multi-case arms
public static void main(String args)
StringDatabase names new AStringDatabase()
while (true) String input
Keyboard.readLine() if
(!(input.length() 0)) if
(input.charAt(0) 'q') break else switch
(input.charAt(0)) case 'p, P
print(names) break case 'd, D
names.deleteElement(input.substring(2,
input.length())) break case 'm,
M System.out.println(names.member(input
.substring(2, input.length()))) break
case 'c, C names.clear()
break default names.addElement(input
)
71
Omitting break
public static void main(String args)
StringDatabase names new AStringDatabase()
while (true) String input
Keyboard.readLine() if
(!(input.length() 0)) if
(input.charAt(0) 'q') break else switch
(input.charAt(0)) case 'p, P
print(names) case 'd, D
names.deleteElement(input.substring(2,
input.length())) case 'm, M
System.out.println(names.member(input.substring(2,
input.length()))) case 'c, C
names.clear() default
names.addElement(input)
72
Illegal Switch
Type of switch expression must be ordinal type
switch (input ) case print
print(names) case clear
names.clear() default
names.addElement(input)
73
Ordinal Type

• Values of type are ordered.
• Each value has a unique successor and predecessor

int
char
String
double