いいかな？
import java.util.*;
public class Greeting
{
public static void main(String[] args)
{
String[] dayOfWeek = {"","日","月","火","水","木","金","土"};
Calendar calendar = Calendar.getInstance();
int hour = calendar.get(Calendar.HOUR_OF_DAY);
System.out.print(
calendar.get(Calendar.YEAR)+"年"
+calendar.get(Calendar.MONTH)+"月"
+calendar.get(Calendar.DAY_OF_MONTH)+"日"
+dayOfWeek[calendar.get(Calendar.DAY_OF_WEEK)]+"曜日"
+calendar.get(Calendar.HOUR_OF_DAY)+"時"
+calendar.get(Calendar.MINUTE)+"分"
+calendar.get(Calendar.SECOND)+"秒です。"
);
if (5 <= hour && hour < 12)
System.out.println("おはよう");
else if (12 <= hour && hour < 16)
System.out.println("こんにちは");
else
System.out.println("こんばんは");
}
}