Classes and Objects

Program Chapter 8 Classes and Objects: A Deeper Look (8.1 - 8.6)

8.1 Time1 class declaration maintains the time in 24-hour format 

1. /**  
2.   * Program Kelas Time1  
3.   * Deklarasi kelas Time1 mengelola waktu dalam format 24 jam  
4.   * Nama file : Time1.java  
5.   */
7. public class Time
8. {
9.     private int hour;
10.     private int minute;
11.     private int second;
12.    
13.     public void setTime (int h, int m, int s)
14.     {
15.         if((h>=0 && h<24) && (m>=0 && m<60) && (s>=0 && s<60))
16.         {
17.             hour=h;
18.             minute=s;
19.             second=s;
20.         }
21.         else
22.             throw new IllegalArgumentException("hour, minute and/or second was out of range");
23.     }
24.    
25.     public String toUniversalString()
26.     {
27.         return String.format("%02d:%02d:%02", hour, minute, second);
28.     }
29.    
30.     public String toString()
31.     {
32.         return String.format("%d:%02d:%02d %s",
33.         ((hour==0 || hour==12)?12:hour%12),
34.         minute, second, (hour<12? "AM" : "PM"));
35.     }
36. }

8.2 Time1 object used in an application 

1. /**  
2.   * Program Kelas Time1Test  
3.   * Objek Time1 digunakan dalam aplikasi  
4.   * nama file : Time1Test.java  
5.   */  
7. public class Time1Test  
8.  {  
9.    public static void main( String[] args )  
10.    {  
11.      Time1 time = new Time1();  
13.      System.out.print( "The initial universal time is: ");  
14.      System.out.println(time.toUniversalString() );  
15.      System.out.print( "The initial standard time is: ");  
16.      System.out.println(time.toString() );  
17.      System.out.println();  
19.      time.setTime( 13, 27, 6);  
20.      System.out.print( "Universal time after setTime is: ");  
21.      System.out.println(time.toUniversalString() );  
22.      System.out.print("Standard time after setTime is: ");  
23.      System.out.println( time.toString() );  
24.      System.out.println();  
26.      try  
27.      {  
28.        time.setTime( 99, 99 , 99 );  
29.      }  
30.      catch ( IllegalArgumentException e )  
31.      {  
32.        System.out.printf( "Exception: %s\n\n", e.getMessage() );  
33.      }  
34.      System.out.println( "After attempting invalid settings:");  
35.      System.out.print( "Universal time: ");  
36.      System.out.println(time.toUniversalString() );  
37.      System.out.print("Standard time: ");  
38.      System.out.println( time.toString() );  
39.    }  
40.  }

Output:



8.3 Controlling Access to Members 

1. /**  
2.  * Program Kelas MemberAccessTest  
3.  * Anggota kelas private Time1 tidak dapat diakses  
4.  * Nama file : MemberAccessTest.java  
5.  */  
6.    
7. public class MemberAccessTest
8. {
9.    public static void main(String[] args)
10.    {
11.        Time1 time = new Time1();
12.        
13.        time.hour = 7; //error: has private access
14.        time.minute = 15; //error: has private access
15.        time.second = 30; //error: has private access
16.    }
17. }

8.4 Referring to the Current Object's Members with the this Reference 

1. /**  
2.  * Program Kelas ThisTest  
3.  * Program ini digunakan secara implisit dan eksplisit untuk merujuk kepada anggota dari sebuah objek  
4.  * Nama file : ThisTest.java  
5.  */  
7. public class ThisTest
8. {
9.     public static void main (String[] args)
10.     {
11.         SimpleTime time = new SimpleTime(15, 30, 19);
12.         System.out.println(time.buildString());
13.     }
14. }
16. class SimpleTime
17. {
18.     private int hour;
19.     private int minute;
20.     private int second;
21.    
22.     public SimpleTime(int hour, int minute, int second)
23.     {
24.         this.hour=hour;
25.         this.minute=minute;
26.         this.second=second;
27.     }
28.    
29.     public String buildString()
30.     {
31.         return String.format("%24s: %s\n%24s: %s",
32.             "this.toUniversalString()", this.toUniversalString(),
33.             "toUniversalString()", toUniversalString());
34.     }
35.    
36.     public String toUniversalString()
37.     {
38.         return String.format( "%02d:%02d:%02d",
39.             this.hour, this.minute, this.second);
40.     }
41. }

Output:




8.5 Time2 class with overloaded constructors

1. /**  
2.   * Program Kelas Time2  
3.   * Deklarasi kelas Time2 dengan konstuktor overload  
4.   * Nama file : Time2.java  
5.   */
7. public class Time2
8. {
9.     private int hour;
10.     private int minute;
11.     private int second;
12.    
13.     public Time2()
14.     {
15.         this( 0, 0, 0 );
16.     }
17.    
18.     public Time2( int h )
19.     {
20.         this( h, 0, 0 );
21.     }
22.    
23.     public Time2( int h, int m )
24.     {
25.         this( h, m, 0 );
26.     }
27.    
28.     public Time2( int h, int m, int s )
29.     {
30.         setTime( h, m, s );
31.     }
32.    
33.     public Time2( Time2 time )
34.     {
35.         this( time.getHour(), time.getMinute(), time.getSecond() );
36.     }
37.    
38.     public void setTime( int h, int m, int s )
39.     {
40.         setHour( h );
41.         setMinute( m );
42.         setSecond( s );
43.     }
45.     public void setHour( int h )
46.     {
47.         if ( h >= 0 && h < 24 )
48.             hour = h;
49.         else
50.             throw new IllegalArgumentException( "hour must be 0-23" );
51.     }
53.     public void setMinute( int m )
54.     {
55.         if ( m >= 0 && m < 60 )
56.             minute = m;
57.         else
58.             throw new IllegalArgumentException( "minute must be 0-59" );
59.     }
61.     public void setSecond( int s )
62.     {
63.         if ( s >= 0 && s < 60 )
64.             second = ( ( s >= 0 && s < 60 ) ? s : 0 );
65.         else
66.             throw new IllegalArgumentException( "second must be 0-59" );
67.     }
69.     public int getHour()
70.     {
71.         return hour;
72.     }
74.     public int getMinute()
75.     {
76.         return minute;
77.     }
78.    
79.     public int getSecond()
80.     {
81.         return second;
82.     }
84.     public String toUniversalString()
85.     {
86.         return String.format(
87.             "%02d:%02d:%02d", getHour(), getMinute(), getSecond() );
88.     }
90.     public String toString()
91.     {
92.         return String.format( "%d:%02d:%02d %s",
93.             ((getHour() == 0 || getHour() == 12) ? 12 : getHour() % 12 ),
94.                 getMinute(), getSecond(), ( getHour() < 12 ? "AM" : "PM" ) );
95.     }
96. }

8.6 Overloaded constructors used to initialize Time2 objects 

1. /**  
2.   * Program Kelas Time2Test  
3.   * Konstruktor overload digunakan untuk menginisialisasi objek Time2  
4.   * Nama file : Time2Test.java  
5.   */  
7. public class Time2Test
8. {
9.     public static void main(String[] args)
10.     {
11.         Time2 t1 = new Time2();
12.         Time2 t2 = new Time2( 2 );
13.         Time2 t3 = new Time2( 21, 34 );
14.         Time2 t4 = new Time2( 12, 25, 42 );
15.         Time2 t5 = new Time2( t4 );
16.        
17.         System.out.println( "Constructed with:" );
18.         System.out.println( "t1: all arguments defaulted" );
19.         System.out.printf( " %s\n", t1.toUniversalString() );
20.         System.out.printf( " %s\n", t1.toString() );
22.         System.out.println(
23.             "t2: hour specified; minute and second defaulted" );
24.         System.out.printf( " %s\n", t2.toUniversalString() );
25.         System.out.printf( " %s\n", t2.toString() );
27.         System.out.println(
28.             "t3: hour and minute specified; second defaulted" );
29.         System.out.printf( " %s\n", t3.toUniversalString() );
30.         System.out.printf( " %s\n", t3.toString() );
32.         System.out.println( "t4: hour, minute and second specified" );
33.         System.out.printf( " %s\n", t4.toUniversalString() );
34.         System.out.printf( " %s\n", t4.toString() );
36.         System.out.println( "t5: Time2 object t4 specified" );
37.         System.out.printf( " %s\n", t5.toUniversalString() );
38.         System.out.printf( " %s\n", t5.toString() );
40.         try
41.         {
42.             Time2 t6 = new Time2( 27, 74, 99 );
43.         }
44.         catch ( IllegalArgumentException e )
45.         {
46.             System.out.printf( "\nException while initializing t6: %s\n",
47.             e.getMessage() );
48.         }
49.     }
50.  }

Output: