Java Increment Date.

Create a program called Date.java to perform error-checking on the initial values for instance: fields month, day and year. Also, provide a method nextDay() to increment the day by one. The Date object should always remain in a consistent state. Write a program that tests the nextDay method in a loop that prints the date during each iteration of the loop to illustrate that the nextDay method works correctly. Test the following cases:

a) incrementing into the next month.

b) incrementing into the next year

What I have so far:
public class Date {

private int day; // 1-31
private int month; // 1-12
private int year; // The year!

// Get Methods
// get the Day
public int getDay()
{
return day;
}

// get the Month
public int getMonth()
{
return month;

}

// get the Year
public int getYear()
{
return year;

}

// Set Methods.
public void setTime( int d, int m, int y )
{
setDay( d ); // set the day
setMonth( m ); // set the month
setYear( y ); // set the year
}

private void setDay(int d) {
}
public Date() { setDay( 07, 20, 2010 ); }

// Time3 constructor: day, month and year supplied.
public Date( int d, int m, int y ) { setDay( d, m, y ); }

// set the day
public void setDay( int d, int i, int j )
{ day = ( ( d >= 0 && d < 32 ) ? d : 0 ); }

// set the month
public void setMonth( int m )
{ month = ( ( m >= 0 && m < 12 ) ? m : 0 ); }

// set the year
public void setYear( int y )
{ year = ( ( y >= 0 && y > 0 ) ? y : 0 ); }

// Change day to next day!
public void nextDay()
{
setDay( day + 1 );
if ( day == 0, day<=31 )
nextDay();
}

// Increment the Month
public void incrementMonth()
{
setMonth( month + 1 );

if ( month == 0, month <12 )
incrementMonth();
}

// Increment the Year
public void incrementYear()
{
setYear( year + 1 );
}
// Convert to String in standard-date format
public String toString()
{
return ( ( month == 12 || month == 0 ) ? 12 : month % 12 ) +
"/" + ( day < 31 ) + year +
"/" + ( year > 0 );
}
}