Classes and Objects

• ·         Fig. 8.1: Time1.java

Time1 class declaration maintains the time in 24-hours format.

public class Time1
{
    public int hour;
    public int minute;
    public int second;
    
    public void setTime(int h, int m, int s)
    {
        if((h >= 0 && h < 24) && (m >= 0 && m < 60) && (s >= 0 && s < 60))
        {
            hour = h;
            minute = m;
            second = s;
        }
        else
            throw new IllegalArgumentException( "hour, minute and/or second was out of range" );
    }
    
    public String toUniversalString()
    {
        return String.format( "%02d:%02d:%02d", hour, minute, second );
    }
    
    public String toString()
    {
        return String.format( "%02d:%02d:%02d %s",
            ((hour == 0 || hour == 12) ? 12 : hour % 12),
            minute, second, (hour < 12 ? "AM" : "PM"));
    }
}

• ·         Fig. 8.2: Time1Test.java

Time1 object used in an application.

public class Time1Test
{
    public static void main( String[] args )
    {
        Time1 time = new Time1();
        
        System.out.print( "The initial universal time is : " );
        System.out.println( time.toUniversalString() );
        System.out.print( "The initial standard time is : " );
        System.out.println( time.toString() );
        System.out.println();
        
        time.setTime( 13, 27, 6 );
        System.out.print( "Universal time after setTime is : " );
        System.out.println( time.toUniversalString() );
        System.out.print( "Standard time after setTime is : " );
        System.out.println( time.toString() );
        System.out.println();
        
        try
        {
            time.setTime( 99, 99, 99 );
        }
        catch ( IllegalArgumentException e )
        {
            System.out.printf( "Exception: %s\n\n", e.getMessage() );
        }
        
        System.out.println( "After attempting invalid settings:" );
        System.out.print( "Universal time: " );
        System.out.println( time.toUniversalString() );
        System.out.print( "Standard time: " );
        System.out.println( time.toString() );
    }
}

           

Output

· 

•  Fig. 8.3: MemberAccessTest.java

Private members of class Time1 are not accessible.

public class MemberAccessTest
{
    public static void main( String[] args )
    {
        Time1 time = new Time1();
        
        time.hour = 7;
        time.minute = 15;
        time.second = 30;
    }
}

• ·         Fig. 8.4: ThisTest.java

This used implicitly and explicitly to refer to members of an object.

public class ThisTest
{
    public static void main ( String[] args )
    {
        SimpleTime time = new SimpleTime( 15, 30, 19 );
        System.out.println( time.buildString() );
    }
}

class SimpleTime
{
    private int hour;
    private int minute;
    private int second;
    
    public SimpleTime( int hour, int minute, int second )
    {
        this.hour = hour;
        this.minute = minute;
        this.second = second;
    }
    
    public String buildString()
    {
        return String.format( "%24s: %s\n%24s: %s",
            "this.toUniversalString()", this.toUniversalString(),
            "toUniversalString()", toUniversalString() );
    }
    
    public String toUniversalString()
    {
        return String.format( "%02d:%02d:%02d", this.hour, this.minute, this.second );
    }
}

Output

•  Fig. 8.5: Time2.java

Time2 class declaration with overloaded cunstructors.

public class Time2
{
    private int hour;
    private int minute;
    private int second;
    
    public Time2()
    {
        this( 0, 0, 0 );
    }
    
    public Time2( int h )
    {
        this( h, 0, 0 );
    }
    
    public Time2( int h, int m )
    {
        this( h, m, 0 );
    }
    
    public Time2( int h, int m, int s )
    {
        setTime( h, m, s );
    }
    
    public Time2( Time2 time )
    {
        this( time.getHour(), time.getMinute(), time.getSecond() );
    }
    
    public void setTime( int h, int m, int s )
    {
        setHour( h );
        setMinute( m );
        setSecond( s );
    }
    
    public void setHour( int h )
    {
        if ( h >= 0 && h < 24 )
            hour = h;
        else
            throw new IllegalArgumentException( "hour must be 0-23" );
    }
    
    public void setMinute( int m )
    {
        if( m >= 0 && m < 60 )
            minute = m;
        else
            throw new IllegalArgumentException( "minute must be 0-59" );
    }
    
    public void setSecond( int s )
    {
        if( s >= 0 && s < 60 )
            second = ( ( s >= 0 && s < 60 ) ? s : 0 );
        else
            throw new IllegalArgumentException( "second must be 0-59" );
    }
    
    public int getHour()
    {
        return hour;
    }
    
    public int getMinute()
    {
        return minute;
    }
    
    public int getSecond()
    {
        return second;
    }
    
    public String toUniversalString()
    {
        return String.format( "%02d:%02d:%02d", getHour(), getMinute(), getSecond() );
    }
    
    public String toString()
    {
        return String.format( "%d:%02d:%02d %s",
            ( (getHour() == 0 || getHour() == 12) ? 12 : getHour() % 12 ),
            getMinute(), getSecond(), ( getHour() < 12 ? "AM" : "PM") );
    }
}   
        

• ·         Fig. 8.6: Time2Test.java

Overloaded cunstructors used to initialize Time2 objects.

public class Time2Test
{
    public static void main( String[] args )
    {
        Time2 t1 = new Time2();
        Time2 t2 = new Time2( 2 );
        Time2 t3 = new Time2( 21, 34 );
        Time2 t4 = new Time2( 12, 25, 42 );
        Time2 t5 = new Time2( t4 );
        
        System.out.println( "Constructed with:" );
        System.out.println( "t1: all arguments defaulted" );
        System.out.printf( "   %s\n", t1.toUniversalString() );
        System.out.printf( "   %s\n", t1.toString() );
        
        System.out.println( "t2: hour specified; minute and second defaulted" );
        System.out.printf( "   %s\n", t2.toUniversalString() );
        System.out.printf( "   %s\n", t2.toString() );
        
        System.out.println( "t3: hour and minute specified; second defaulted" );
        System.out.printf( "   %s\n", t3.toUniversalString() );
        System.out.printf( "   %s\n", t3.toString() );
        
        System.out.println( "t4: hour, minute and second specified" );
        System.out.printf( "   %s\n", t4.toUniversalString() );
        System.out.printf( "   %s\n", t4.toString() );
        
        System.out.println( "t5: Time2 object t4 specified" );
        System.out.printf( "   %s\n", t5.toUniversalString() );
        System.out.printf( "   %s\n", t5.toString() );
        
        try
        {
            Time2 t6 = new Time2( 27, 74, 99 );
        }
        catch ( IllegalArgumentException e )
        {
            System.out.printf( "\nException while initializing t6: %s\n", e.getMessage() );
        }
    }
}

            

Output