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Date Class

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day = 1; month = 1; year = 2000; valid = true; public Date (Date d) // Copy constructor ... public Date (Date d) private void setValidity() // Check day, month, year ... – PowerPoint PPT presentation

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Title: Date Class

1
Date Class

public class Date
private int month
private int day
private int year
private boolean valid
// true if stored date is valid
public Date (int inDay, int inMonth, int
inYear)
day inDay
month inMonth
year inYear
...

public class Date
private int month
private int day
private int year
private boolean valid
// true if stored date is valid ...
private void setValidity()
// Check day, month, year
// Handle 30 day months and leap year
// Leap year expression
// year 400 0 (year 4 0
year 100 ! 0)
if ( . . . )
valid true
else
valid false

public class Date
private int month
private int day
private int year
private boolean valid // true if stored date
is valid
public Date (int inDay, int inMonth, int
inYear)
day inDay
month inMonth
year inYear
setValidity()
public Date (String s)
// Code to parse string to date

public class Date
...
public Date (int inDay, int inMonth, int
inYear)
...
public Date (String s)
...
public Date ()
day 1
month 1
year 2000
valid true
public Date (Date d) // Copy constructor
day d.day
month d.month
year d.year

public class Date
private int month
private int day
private int year
private boolean valid
public Date (int inDay, int inMonth, int
inYear)
...
public Date (String s)
...
public Date ()
...
public Date (Date d)
...
private void setValidity()
...
. . .

public class Date
. . .
public String toString()
return month / day / year
public boolean isValid()
return valid
// More methods

public class Date
. . .
// Object is a base class
// All classes are a sub-class of Object
// An instance of any class inherits the
methods of
// Object class
_at_Override
public String toString()
return month / day / year
//public _at_Override String toString()

8
Date Class
public class Date ... public _at_Override
String toString() return month /
day / year public void setFormat
(int format) // Allow different
formats ...
9
Date Class
public class Date ... // constants that
can be accessed by the user public final int
SHORT_DATE 0 public final int LONG_DATE
1 public final int WEEKDAY 2
private int dateFormat SHORT_DATE ...
10
Date Class
public class Date ... public void
setFormat (int format) // Check
validity of format dateFormat format
public _at_Override String toString()
if (dateFormat shortDate) return
month / day / year else if
(dateFormat longDate) ... else
... ...
11
Date Class

Date d new Date()
System.out.println(d.toString())
d.setFormat(d.longDate)
System.out.println(d.toString())
// Cannot compile!
d.setFormat(Date.weekDay )

12
Date Class
public class Date ... // constants that
can be accessed by the user // adding modifier
static public static final int shortDate
0 public static final int longDate 1
public static final int weekDay 2
private int dateFormat shortDate
... Date d new Date() // Compile and
run! d.setFormat(Date.weekDate)
13
Instance and Static Data

Instance data
private int day, month, year
// Difference instances (objects) usually
// have different values
Static data
private static int count 0
// One value for the class,
// no matter how many instances (could be 0)
// Each constructor must update the value of
count
public Date()
...
count

14
Static Methods
public class Date private static int count
0 . . . public Date() ...
count // static method //
for the class public static int getCount()
// Cannot access instance fields
return count
15
Static Methods
public static int getCount() return
count int theCount Date.getCount() //
theCount 0 Date d theCount
Date.getCount() // theCount 0 d new
Date() theCount Date.getCount() // theCount
1 //Static method can be referenced from
non-static context theCount d.getCount()
16
Instance Methods
public class Date . . . private static
int count 0 public Date() ...
count // instance method
public int getCount() // can access
static fields return count
17
Instance Methods
public int getCount() return count int
theCount Date.getCount() // non-static method
cannot be referenced // from a static
context Date d theCount Date.getCount() //
NO d new Date() theCount Date.getCount() //
No theCount d.getCount() // YES!
18