1 OBJECT-BASED PROGRAMMING CHAPTER 8
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- Oswald Henry
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1 1 OBJECT-BASED PROGRAMMING CHAPTER 8 8 Object-Based Programming 1 // Fig. 8.1: Time1.java 2 // Time1 class definition 3 import java.text.decimalformat; // used for number formatting 4 5 // This class maintains the time in 24-hour format 6 public class Time1 extends Object { 7 private int hour; // private int minute; // private int second; // // Time1 constructor initializes each instance variable 12 // to zero. Ensures that each Time1 object starts in a 13 // consistent state. 14 public Time1() 15 { 16 settime( 0, 0, 0 ); 17 } // Set a new time value using universal time. Perform 20 // validity checks on the data. Set invalid values to zero. 21 public void settime( int h, int m, int s ) 22 { 23 hour = ( ( h >= 0 && h < 24 )? h : 0 ); 24 minute = ( ( m >= 0 && m < 60 )? m : 0 ); 25 second = ( ( s >= 0 && s < 60 )? s : 0 ); 26 } // Convert to String in universal-time format 29 public String touniversalstring() 30 { 31 DecimalFormat twodigits = new DecimalFormat( "00" ); return twodigits.format( hour ) + ":" + 34 twodigits.format( minute ) + ":" + 35 twodigits.format( second ); 36 } // Convert to String in standard-time format 39 public String tostring() 40 { 41 DecimalFormat twodigits = new DecimalFormat( "00" ); return ( (hour == 12 hour == 0)? 12 : hour % 12 ) + 44 ":" + twodigits.format( minute ) + 45 ":" + twodigits.format( second ) + 46 ( hour < 12? " AM" : " PM" ); 47 } 48 } Fig. 8.1 Abstract data type Time1 implementation as a class (part 1 of 2).
2 CHAPTER 8 OBJECT-BASED PROGRAMMING 2 49 // Fig. 8.1: TimeTest.java 50 // Class TimeTest to exercise class Time1 51 import javax.swing.joptionpane; public class TimeTest { 54 public static void main( String args[] ) 55 { 56 Time1 t = new Time1(); // calls Time1 constructor 57 String output; output = "The initial universal time is: " + 60 t.touniversalstring() + 61 "\nthe initial standard time is: " + 62 t.tostring() + 63 "\nimplicit tostring() call: " + t; t.settime( 13, 27, 6 ); 66 output += "\n\nuniversal time after settime is: " + 67 t.touniversalstring() + 68 "\nstandard time after settime is: " + 69 t.tostring(); t.settime( 99, 99, 99 ); // all invalid values 72 output += "\n\nafter attempting invalid settings: " + 73 "\nuniversal time: " + t.touniversalstring() + 74 "\nstandard time: " + t.tostring(); JOptionPane.showMessageDialog( null, output, 77 "Testing Class Time1", 78 JOptionPane.INFORMATION_MESSAGE ); System.exit( 0 ); 81 } 82 } Fig. 8.1 Abstract data type Time1 implementation as a class (part 2 of 2).
3 3 OBJECT-BASED PROGRAMMING CHAPTER 8 1 // Fig. 8.2: TimeTest.java 2 // Demonstrate errors resulting from attempts 3 // to access private class members. 4 public class TimeTest { 5 public static void main( String args[] ) 6 { 7 Time1 t = new Time1(); 8 9 t.hour = 7; 10 } 11 } TimeTest.java:9: Variable hour in class Time1 not accessible from class TimeTest. t.hour = 7; ^ 1 error Fig. 8.2 Erroneous attempt to access private members of a class.
4 CHAPTER 8 OBJECT-BASED PROGRAMMING 4 1 // Fig. 8.3: Time1.java 2 // Time1 class definition 3 package com.deitel.jhtp3.ch08; 4 import java.text.decimalformat; // used for number formatting 5 6 // This class maintains the time in 24-hour format 7 public class Time1 extends Object { 8 private int hour; // private int minute; // private int second; // // Time1 constructor initializes each instance variable 13 // to zero. Ensures that each Time1 object starts in a 14 // consistent state. 15 public Time1() 16 { 17 settime( 0, 0, 0 ); 18 } // Set a new time value using military time. Perform 21 // validity checks on the data. Set invalid values 22 // to zero. 23 public void settime( int h, int m, int s ) 24 { 25 hour = ( ( h >= 0 && h < 24 )? h : 0 ); 26 minute = ( ( m >= 0 && m < 60 )? m : 0 ); 27 second = ( ( s >= 0 && s < 60 )? s : 0 ); 28 } // Convert to String in universal-time format 31 public String touniversalstring() 32 { 33 DecimalFormat twodigits = new DecimalFormat( "00" ); return twodigits.format( hour ) + ":" + 36 twodigits.format( minute ) + ":" + 37 twodigits.format( second ); 38 } // Convert to String in standard-time format 41 public String tostring() 42 { 43 DecimalFormat twodigits = new DecimalFormat( "00" ); return ( (hour == 12 hour == 0)? 12 : hour % 12 ) + 46 ":" + twodigits.format( minute ) + 47 ":" + twodigits.format( second ) + 48 ( hour < 12? " AM" : " PM" ); 49 } 50 } Fig. 8.3 Creating a package for software reuse (part 1 of 2).
5 5 OBJECT-BASED PROGRAMMING CHAPTER 8 51 // Fig. 8.3: TimeTest.java 52 // Class TimeTest to use imported class Time1 53 import javax.swing.joptionpane; 54 import com.deitel.jhtp3.ch08.time1; // import Time1 class public class TimeTest { 57 public static void main( String args[] ) 58 { 59 Time1 t = new Time1(); t.settime( 13, 27, 06 ); 62 String output = 63 "Universal time is: " + t.touniversalstring() + 64 "\nstandard time is: " + t.tostring(); JOptionPane.showMessageDialog( null, output, 67 "Packaging Class Time1 for Reuse", 68 JOptionPane.INFORMATION_MESSAGE ); System.exit( 0 ); 71 } 72 } Fig. 8.3 Creating a package for software reuse (part 2 of 2).
6 CHAPTER 8 OBJECT-BASED PROGRAMMING 6 1 // Fig. 8.4: Time2.java 2 // Time2 class definition 3 package com.deitel.jhtp3.ch08; // place Time2 in a package 4 import java.text.decimalformat; // used for number formatting 5 6 // This class maintains the time in 24-hour format 7 public class Time2 extends Object { 8 private int hour; // private int minute; // private int second; // // Time2 constructor initializes each instance variable 13 // to zero. Ensures that Time object starts in a 14 // consistent state. 15 public Time2() { settime( 0, 0, 0 ); } // Time2 constructor: hour supplied, minute and second 18 // defaulted to public Time2( int h ) { settime( h, 0, 0 ); } // Time2 constructor: hour and minute supplied, second 22 // defaulted to public Time2( int h, int m ) { settime( h, m, 0 ); } // Time2 constructor: hour, minute and second supplied. 26 public Time2( int h, int m, int s ) { settime( h, m, s ); } // Time2 constructor: another Time2 object supplied. 29 public Time2( Time2 time ) 30 { 31 settime( time.hour, time.minute, time.second ); 32 } // Set a new time value using universal time. Perform 35 // validity checks on the data. Set invalid values to zero. 36 public void settime( int h, int m, int s ) 37 { 38 hour = ( ( h >= 0 && h < 24 )? h : 0 ); 39 minute = ( ( m >= 0 && m < 60 )? m : 0 ); 40 second = ( ( s >= 0 && s < 60 )? s : 0 ); 41 } // Convert to String in universal-time format 44 public String touniversalstring() 45 { 46 DecimalFormat twodigits = new DecimalFormat( "00" ); 47 Fig. 8.4 Using overloaded constructors (part 1 of 4).
7 7 OBJECT-BASED PROGRAMMING CHAPTER 8 48 return twodigits.format( hour ) + ":" + 49 twodigits.format( minute ) + ":" + 50 twodigits.format( second ); 51 } // Convert to String in standard-time format 54 public String tostring() 55 { 56 DecimalFormat twodigits = new DecimalFormat( "00" ); return ( (hour == 12 hour == 0)? 12 : hour % 12 ) + 59 ":" + twodigits.format( minute ) + 60 ":" + twodigits.format( second ) + 61 ( hour < 12? " AM" : " PM" ); 62 } 63 } Fig. 8.4 Using overloaded constructors (part 2 of 4).
8 CHAPTER 8 OBJECT-BASED PROGRAMMING 8 64 // Fig. 8.4: TimeTest.java 65 // Using overloaded constructors 66 import javax.swing.*; 67 import com.deitel.jhtp3.ch08.time2; public class TimeTest { 70 public static void main( String args[] ) 71 { 72 Time2 t1, t2, t3, t4, t5, t6; 73 String output; t1 = new Time2(); 76 t2 = new Time2( 2 ); 77 t3 = new Time2( 21, 34 ); 78 t4 = new Time2( 12, 25, 42 ); 79 t5 = new Time2( 27, 74, 99 ); 80 t6 = new Time2( t4 ); // use t4 as initial value output = "Constructed with: " + 83 "\nt1: all arguments defaulted" + 84 "\n " + t1.touniversalstring() + 85 "\n " + t1.tostring(); output += "\nt2: hour specified; minute and " + 88 "second defaulted" + 89 "\n " + t2.touniversalstring() + 90 "\n " + t2.tostring(); output += "\nt3: hour and minute specified; " + 93 "second defaulted" + 94 "\n " + t3.touniversalstring() + 95 "\n " + t3.tostring(); 96 Fig. 8.4 Using overloaded constructors (part 3 of 4).
9 9 OBJECT-BASED PROGRAMMING CHAPTER 8 97 output += "\nt4: hour, minute, and second specified" + 98 "\n " + t4.touniversalstring() + 99 "\n " + t4.tostring(); output += "\nt5: all invalid values specified" "\n " + t5.touniversalstring() "\n " + t5.tostring(); output += "\nt6: Time2 object t4 specified" "\n " + t6.touniversalstring() "\n " + t6.tostring(); JOptionPane.showMessageDialog( null, output, 110 "Demonstrating Overloaded Constructors", 111 JOptionPane.INFORMATION_MESSAGE ); System.exit( 0 ); 114 } 115 } Fig. 8.4 Using overloaded constructors (part 4 of 4).
10 CHAPTER 8 OBJECT-BASED PROGRAMMING 10 1 // Fig. 8.5: Time3.java 2 // Time3 class definition 3 package com.deitel.jhtp3.ch08; // place Time3 in a package 4 import java.text.decimalformat; // used for number formatting 5 6 // This class maintains the time in 24-hour format 7 public class Time3 extends Object { 8 private int hour; // private int minute; // private int second; // // Time3 constructor initializes each instance variable 13 // to zero. Ensures that Time object starts in a 14 // consistent state. 15 public Time3() { settime( 0, 0, 0 ); } // Time3 constructor: hour supplied, minute and second 18 // defaulted to public Time3( int h ) { settime( h, 0, 0 ); } // Time3 constructor: hour and minute supplied, second 22 // defaulted to public Time3( int h, int m ) { settime( h, m, 0 ); } // Time3 constructor: hour, minute and second supplied. 26 public Time3( int h, int m, int s ) { settime( h, m, s ); } // Time3 constructor: another Time3 object supplied. 29 public Time3( Time3 time ) 30 { 31 settime( time.gethour(), 32 time.getminute(), 33 time.getsecond() ); 34 } // Set Methods 37 // Set a new time value using universal time. Perform 38 // validity checks on the data. Set invalid values to zero. 39 public void settime( int h, int m, int s ) 40 { 41 sethour( h ); // set the hour 42 setminute( m ); // set the minute 43 setsecond( s ); // set the second 44 } // set the hour 47 public void sethour( int h ) 48 { hour = ( ( h >= 0 && h < 24 )? h : 0 ); } Fig. 8.5 Using set and get methods (part 1 of 6).
11 11 OBJECT-BASED PROGRAMMING CHAPTER // set the minute 51 public void setminute( int m ) 52 { minute = ( ( m >= 0 && m < 60 )? m : 0 ); } // set the second 55 public void setsecond( int s ) 56 { second = ( ( s >= 0 && s < 60 )? s : 0 ); } // Get Methods 59 // get the hour 60 public int gethour() { return hour; } // get the minute 63 public int getminute() { return minute; } // get the second 66 public int getsecond() { return second; } // Convert to String in universal-time format 69 public String touniversalstring() 70 { 71 DecimalFormat twodigits = new DecimalFormat( "00" ); return twodigits.format( gethour() ) + ":" + 74 twodigits.format( getminute() ) + ":" + 75 twodigits.format( getsecond() ); 76 } // Convert to String in standard-time format 79 public String tostring() 80 { 81 DecimalFormat twodigits = new DecimalFormat( "00" ); return ( ( gethour() == 12 gethour() == 0 )? : gethour() % 12 ) + ":" + 85 twodigits.format( getminute() ) + ":" + 86 twodigits.format( getsecond() ) + 87 ( gethour() < 12? " AM" : " PM" ); 88 } 89 } Fig. 8.5 Using set and get methods (part 2 of 6).
12 CHAPTER 8 OBJECT-BASED PROGRAMMING // Fig. 8.5: TimeTest.java 91 // Demonstrating the Time3 class set and get methods 92 import java.awt.*; 93 import java.awt.event.*; 94 import javax.swing.*; 95 import com.deitel.jhtp3.ch08.time3; public class TimeTest extends JApplet 98 implements ActionListener { 99 private Time3 t; 100 private JLabel hourlabel, minutelabel, secondlabel; 101 private JTextField hourfield, minutefield, 102 secondfield, display; 103 private JButton tickbutton; public void init() 106 { 107 t = new Time3(); Container c = getcontentpane(); c.setlayout( new FlowLayout() ); 112 hourlabel = new JLabel( "Set Hour" ); 113 hourfield = new JTextField( 10 ); 114 hourfield.addactionlistener( this ); 115 c.add( hourlabel ); 116 c.add( hourfield ); minutelabel = new JLabel( "Set minute" ); 119 minutefield = new JTextField( 10 ); 120 minutefield.addactionlistener( this ); 121 c.add( minutelabel ); 122 c.add( minutefield ); secondlabel = new JLabel( "Set Second" ); 125 secondfield = new JTextField( 10 ); 126 secondfield.addactionlistener( this ); 127 c.add( secondlabel ); 128 c.add( secondfield ); display = new JTextField( 30 ); 131 display.seteditable( false ); 132 c.add( display ); tickbutton = new JButton( "Add 1 to Second" ); 135 tickbutton.addactionlistener( this ); 136 c.add( tickbutton ); updatedisplay(); 139 } 140 Fig. 8.5 Using set and get methods (part 3 of 6).
13 13 OBJECT-BASED PROGRAMMING CHAPTER public void actionperformed( ActionEvent e ) 142 { 143 if ( e.getsource() == tickbutton ) 144 tick(); 145 else if ( e.getsource() == hourfield ) { 146 t.sethour( 147 Integer.parseInt( e.getactioncommand() ) ); 148 hourfield.settext( "" ); 149 } 150 else if ( e.getsource() == minutefield ) { 151 t.setminute( 152 Integer.parseInt( e.getactioncommand() ) ); 153 minutefield.settext( "" ); 154 } 155 else if ( e.getsource() == secondfield ) { 156 t.setsecond( 157 Integer.parseInt( e.getactioncommand() ) ); 158 secondfield.settext( "" ); 159 } updatedisplay(); 162 } public void updatedisplay() 165 { 166 display.settext( "Hour: " + t.gethour() "; Minute: " + t.getminute() "; Second: " + t.getsecond() ); 169 showstatus( "Standard time is: " + t.tostring() "; Universal time is: " + t.touniversalstring() ); 171 } public void tick() 174 { 175 t.setsecond( ( t.getsecond() + 1 ) % 60 ); if ( t.getsecond() == 0 ) { 178 t.setminute( ( t.getminute() + 1 ) % 60 ); if ( t.getminute() == 0 ) 181 t.sethour( ( t.gethour() + 1 ) % 24 ); 182 } 183 } 184 } Fig. 8.5 Using set and get methods (part 4 of 6).
14 CHAPTER 8 OBJECT-BASED PROGRAMMING 14 Fig. 8.5 Using set and get methods (part 5 of 6).
15 15 OBJECT-BASED PROGRAMMING CHAPTER 8 Fig. 8.5 Using set and get methods (part 6 of 6).
16 CHAPTER 8 OBJECT-BASED PROGRAMMING 16 1 // Fig. 8.6: Increment.java 2 // Initializing a final variable 3 import java.awt.*; 4 import java.awt.event.*; 5 import javax.swing.*; 6 7 public class Increment extends JApplet 8 implements ActionListener { 9 private int count = 0, total = 0; 10 private final int INCREMENT = 5; // constant variable private JButton incr; Fig. 8.6 Initializing a final variable (part 1 of 2) public void init() 15 { 16 Container c = getcontentpane(); incr = new JButton( "Click to increment" ); 19 incr.addactionlistener( this ); 20 c.add( incr ); 21 } public void actionperformed( ActionEvent e ) 24 { 25 total += INCREMENT; 26 count++; 27 showstatus( "After increment " + count + 28 ": total = " + total ); 29 } 30 } Fig. 8.6 Initializing a final variable (part 2 of 2).
17 17 OBJECT-BASED PROGRAMMING CHAPTER 8 Increment.java:10: Blank final variable 'increment' may not have been initialized. It must be assigned a value in an initializer, or in every constructor. private final int increment; // constant variable ^ 1 error Fig. 8.7 Compiler error message as a result of not initializing increment.
18 CHAPTER 8 OBJECT-BASED PROGRAMMING 18 1 // Fig. 8.8: Date.java 2 // Declaration of the Date class. 3 package com.deitel.jhtp3.ch08; 4 5 public class Date extends Object { 6 private int month; // private int day; // 1-31 based on month 8 private int year; // any year 9 10 // Constructor: Confirm proper value for month; 11 // call method checkday to confirm proper 12 // value for day. 13 public Date( int mn, int dy, int yr ) 14 { 15 if ( mn > 0 && mn <= 12 ) // validate the month 16 month = mn; 17 else { 18 month = 1; 19 System.out.println( "Month " + mn + 20 " invalid. Set to month 1." ); 21 } year = yr; // could also check 24 day = checkday( dy ); // validate the day System.out.println( 27 "Date object constructor for date " + tostring() ); 28 } // Utility method to confirm proper day value 31 // based on month and year. 32 private int checkday( int testday ) 33 { 34 int dayspermonth[] = { 0, 31, 28, 31, 30, 35 31, 30, 31, 31, 30, 36 31, 30, 31 }; if ( testday > 0 && testday <= dayspermonth[ month ] ) 39 return testday; 40 Fig. 8.8 Demonstrating an object with a member object reference (part 1 of 4).
19 19 OBJECT-BASED PROGRAMMING CHAPTER 8 41 if ( month == 2 && // February: Check for leap year 42 testday == 29 && 43 ( year % 400 == 0 44 ( year % 4 == 0 && year % 100!= 0 ) ) ) 45 return testday; System.out.println( "Day " + testday + 48 " invalid. Set to day 1." ); return 1; // leave object in consistent state 51 } // Create a String of the form month/day/year 54 public String tostring() 55 { return month + "/" + day + "/" + year; } 56 } Fig. 8.8 Demonstrating an object with a member object reference (part 2 of 4).
20 CHAPTER 8 OBJECT-BASED PROGRAMMING // Fig. 8.8: Employee.java 58 // Declaration of the Employee class. 59 package com.deitel.jhtp3.ch08; public class Employee extends Object { 62 private String firstname; 63 private String lastname; 64 private Date birthdate; 65 private Date hiredate; public Employee( String fname, String lname, 68 int bmonth, int bday, int byear, 69 int hmonth, int hday, int hyear) 70 { 71 firstname = fname; 72 lastname = lname; 73 birthdate = new Date( bmonth, bday, byear ); 74 hiredate = new Date( hmonth, hday, hyear ); 75 } public String tostring() 78 { 79 return lastname + ", " + firstname + 80 " Hired: " + hiredate.tostring() + 81 " Birthday: " + birthdate.tostring(); 82 } 83 } Fig. 8.8 Demonstrating an object with a member object reference (part 3 of 4).
21 21 OBJECT-BASED PROGRAMMING CHAPTER 8 84 // Fig. 8.8: EmployeeTest.java 85 // Demonstrating an object with a member object. 86 import javax.swing.joptionpane; 87 import com.deitel.jhtp3.ch08.employee; public class EmployeeTest { 90 public static void main( String args[] ) 91 { 92 Employee e = new Employee( "Bob", "Jones", 7, 24, 49, 93 3, 12, 88 ); 94 JOptionPane.showMessageDialog( null, e.tostring(), 95 "Testing Class Employee", 96 JOptionPane.INFORMATION_MESSAGE ); System.exit( 0 ); 99 } 100 } Date object constructor for date 7/24/1949 Date object constructor for date 3/12/1988 Fig. 8.8 Demonstrating an object with a member object reference (part 4 of 4).
22 CHAPTER 8 OBJECT-BASED PROGRAMMING 22 1 // Fig. 8.9: PackageDataTest.java 2 // Classes in the same package (i.e., the same directory) 3 // can use package access data of other classes in the 4 // same package. 5 import javax.swing.joptionpane; 6 7 public class PackageDataTest { 8 public static void main( String args[] ) 9 { 10 PackageData d = new PackageData(); 11 String output; output = "After instantiation:\n" + d.tostring(); d.x = 77; // changing package access data 16 d.s = "Good bye"; // changing package access data output += "\nafter changing values:\n" + d.tostring(); 19 JOptionPane.showMessageDialog( null, output, 20 "Demonstrating Package Access", 21 JOptionPane.INFORMATION_MESSAGE ); System.exit( 0 ); 24 } 25 } class PackageData { 28 int x; // package access instance variable 29 String s; // package access instance variable // constructor 32 public PackageData() 33 { 34 x = 0; 35 s = "Hello"; 36 } public String tostring() 39 { 40 return "x: " + x + " s: " + s; 41 } 42 } Fig. 8.9 Package access to members of a class.
23 23 OBJECT-BASED PROGRAMMING CHAPTER 8 1 // Fig. 8.10: ThisTest.java 2 // Using the this reference to refer to 3 // instance variables and methods. 4 import javax.swing.*; 5 import java.text.decimalformat; 6 7 public class ThisTest { 8 public static void main( String args[] ) 9 { 10 SimpleTime t = new SimpleTime( 12, 30, 19 ); JOptionPane.showMessageDialog( null, t.buildstring(), 13 "Demonstrating the \"this\" Reference", 14 JOptionPane.INFORMATION_MESSAGE ); System.exit( 0 ); 17 } 18 } class SimpleTime { 21 private int hour, minute, second; public SimpleTime( int hour, int minute, int second ) 24 { 25 this.hour = hour; 26 this.minute = minute; 27 this.second = second; 28 } public String buildstring() 31 { 32 return "this.tostring(): " + this.tostring() + 33 "\ntostring(): " + tostring() + 34 "\nthis (with implicit tostring() call): " + 35 this; 36 } public String tostring() 39 { 40 DecimalFormat twodigits = new DecimalFormat( "00" ); return twodigits.format( this.hour ) + ":" + 43 twodigits.format( this.minute ) + ":" + 44 twodigits.format( this.second ); 45 } 46 } Fig Using the this reference (part 1 of 2).
24 CHAPTER 8 OBJECT-BASED PROGRAMMING 24 Fig Using the this reference (part 2 of 2).
25 25 OBJECT-BASED PROGRAMMING CHAPTER 8 1 // Fig. 8.11: Time4.java 2 // Time4 class definition 3 package com.deitel.jhtp3.ch08; // place Time4 in a package 4 import java.text.decimalformat; // used for number formatting 5 6 // This class maintains the time in 24-hour format 7 public class Time4 extends Object { 8 private int hour; // private int minute; // private int second; // // Time4 constructor initializes each instance variable 13 // to zero. Ensures that Time object starts in a 14 // consistent state. 15 public Time4() { this.settime( 0, 0, 0 ); } // Time4 constructor: hour supplied, minute and second 18 // defaulted to public Time4( int h ) { this.settime( h, 0, 0 ); } // Time4 constructor: hour and minute supplied, second 22 // defaulted to public Time4( int h, int m ) { this.settime( h, m, 0 ); } // Time4 constructor: hour, minute and second supplied. 26 public Time4( int h, int m, int s ) 27 { this.settime( h, m, s ); } // Time4 constructor: another Time4 object supplied. 30 public Time4( Time4 time ) 31 { 32 this.settime( time.gethour(), 33 time.getminute(), 34 time.getsecond() ); 35 } 36 Fig Chaining method calls (part 1 of 5).
26 CHAPTER 8 OBJECT-BASED PROGRAMMING // Set Methods 38 // Set a new Time value using military time. Perform 39 // validity checks on the data. Set invalid values to zero. 40 public Time4 settime( int h, int m, int s ) 41 { 42 this.sethour( h ); // set the hour 43 this.setminute( m ); // set the minute 44 this.setsecond( s ); // set the second return this; // enables chaining 47 } // set the hour 50 public Time4 sethour( int h ) 51 { 52 this.hour = ( ( h >= 0 && h < 24 )? h : 0 ); return this; // enables chaining 55 } // set the minute 58 public Time4 setminute( int m ) 59 { 60 this.minute = ( ( m >= 0 && m < 60 )? m : 0 ); return this; // enables chaining 63 } // set the second 66 public Time4 setsecond( int s ) 67 { 68 this.second = ( ( s >= 0 && s < 60 )? s : 0 ); return this; // enables chaining 71 } // Get Methods 74 // get the hour 75 public int gethour() { return this.hour; } // get the minute 78 public int getminute() { return this.minute; } // get the second 81 public int getsecond() { return this.second; } // Convert to String in universal-time format 84 public String touniversalstring() 85 { 86 DecimalFormat twodigits = new DecimalFormat( "00" ); 87 Fig Chaining method calls (part 2 of 5).
27 27 OBJECT-BASED PROGRAMMING CHAPTER 8 88 return twodigits.format( this.gethour() ) + ":" + 89 twodigits.format( this.getminute() ) + ":" + 90 twodigits.format( this.getsecond() ); 91 } // Convert to String in standard-time format 94 public String tostring() 95 { 96 DecimalFormat twodigits = new DecimalFormat( "00" ); return ( ( this.gethour() == this.gethour() == 0 )? : this.gethour() % 12 ) + ":" twodigits.format( this.getminute() ) + ":" twodigits.format( this.getsecond() ) ( this.gethour() < 12? " AM" : " PM" ); 104 } 105 } Fig Chaining method calls (part 3 of 5).
28 CHAPTER 8 OBJECT-BASED PROGRAMMING // Fig. 8.11: TimeTest.java 107 // Chaining method calls together with the this reference 108 import javax.swing.*; 109 import com.deitel.jhtp3.ch08.time4; public class TimeTest { 112 public static void main( String args[] ) 113 { 114 Time4 t = new Time4(); 115 String output; t.sethour( 18 ).setminute( 30 ).setsecond( 22 ); output = "Universal time: " + t.touniversalstring() "\nstandard time: " + t.tostring() "\n\nnew standard time: " t.settime( 20, 20, 20 ).tostring(); JOptionPane.showMessageDialog( null, output, 125 "Chaining Method Calls", 126 JOptionPane.INFORMATION_MESSAGE ); System.exit( 0 ); 129 } 130 } Fig Chaining method calls (part 4 of 5). Fig Chaining method calls (part 5 of 5).
29 29 OBJECT-BASED PROGRAMMING CHAPTER 8 1 // Fig. 8.12: Employee.java 2 // Declaration of the Employee class. 3 public class Employee extends Object { 4 private String firstname; 5 private String lastname; 6 private static int count; // # of objects in memory 7 8 public Employee( String fname, String lname ) 9 { 10 firstname = fname; 11 lastname = lname; count; // increment static count of employees 14 System.out.println( "Employee object constructor: " + 15 firstname + " " + lastname ); 16 } protected void finalize() 19 { 20 --count; // decrement static count of employees 21 System.out.println( "Employee object finalizer: " + 22 firstname + " " + lastname + 23 "; count = " + count ); 24 } public String getfirstname() { return firstname; } public String getlastname() { return lastname; } public static int getcount() { return count; } 31 } Fig Using a static class variable to maintain a count of the number of objects of a class (part 1 of 3).
30 CHAPTER 8 OBJECT-BASED PROGRAMMING // Fig. 8.12: EmployeeTest.java 33 // Test Employee class with static class variable, 34 // static class method, and dynamic memory. 35 import javax.swing.*; public class EmployeeTest { 38 public static void main( String args[] ) 39 { 40 String output; output = "Employees before instantiation: " + 43 Employee.getCount(); Employee e1 = new Employee( "Susan", "Baker" ); 46 Employee e2 = new Employee( "Bob", "Jones" ); output += "\n\nemployees after instantiation: " + 49 "\nvia e1.getcount(): " + e1.getcount() + 50 "\nvia e2.getcount(): " + e2.getcount() + 51 "\nvia Employee.getCount(): " + 52 Employee.getCount(); output += "\n\nemployee 1: " + e1.getfirstname() + 55 " " + e1.getlastname() + 56 "\nemployee 2: " + e2.getfirstname() + 57 " " + e2.getlastname(); // mark objects referred to by e1 and e2 60 // for garbage collection 61 e1 = null; 62 e2 = null; System.gc(); // suggest that garbage collector be called output += "\n\nemployees after System.gc(): " + 67 Employee.getCount(); JOptionPane.showMessageDialog( null, output, 70 "Static Members and Garbage Collection", 71 JOptionPane.INFORMATION_MESSAGE ); 72 System.exit( 0 ); 73 } 74 } Fig Using a static class variable to maintain a count of the number of objects of a class (part 2 of 3).
31 31 OBJECT-BASED PROGRAMMING CHAPTER 8 Employee object constructor: Susan Baker Employee object constructor: Bob Jones Employee object finalizer: Susan Baker; count = 1 Employee object finalizer: Bob Jones; count = 0 Fig Using a static class variable to maintain a count of the number of objects of a class (part 3 of 3).
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