encontrar el dia año y mes ingresando el numero de dias
import java.io.*;
class problm19{
public static void main(String[] args)throws IOException
{
BufferedReader in=new BufferedReader(new
InputStreamReader (System.in));
System.out.print("Ingrese el dia:");
double a
=Double.valueOf(in.readLine().trim()).doubleValue();
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System.out.print("Ingrese el año:");
double b
=Double.valueOf(in.readLine().trim()).doubleValue();
if (a<=31)
{ System.out.println(a+"/ "+01+"/
"+b);
}
else if(a<=59)
{a=a-31;
System.out.println(a+"/ "+02+"/ "+b);
}
else if(a<=90)
{a=a-59;
System.out.println(a+"/ "+03+"/ "+b);
}
else if(a<=120)
{ System.out.println(a+"/ "+04+"/
"+b);
}
else if(a<=151)
{a=a-120;
System.out.println(a+"/ "+05+"/ "+b);
}
else if(a<=181)
{a=a-151;
System.out.println(a+"/ "+06+"/ "+b);
}
else if(a<=212)
{a=a-181;
System.out.println(a+"/ "+07+"/ "+b);
}
else if(a<=243)
{a=a-212;
System.out.println(a+"/ "+8+"/ "+b);
}
else if(a<=274)
{a=a-243;
System.out.println(a+"/ "+9+"/ "+b);
}
else if(a<=304)
{a=a-274;
System.out.println(a+"/ "+10+"/ "+b);
}
else if(a<=334)
{a=a-304;
System.out.println(a+"/ "+11+"/ "+b);
}
else if(a<=365)
{a=a-334;
System.out.println(a+"/ "+12+"/ "+b);
}
else
{double m=a/365;
int j=(int)m;
a=a%365;
b=b+j;
if (a<=31)
{ System.out.println(a+"/ "+01+"/
"+b);
}
else if(a<=59)
{a=a-31;
System.out.println(a+"/ "+02+"/ "+b);
}
else if(a<=90)
{a=a-59;
System.out.println(a+"/ "+03+"/ "+b);
}
else if(a<=120)
{ System.out.println(a+"/ "+04+"/
"+b);
}
else if(a<=151)
{a=a-120;
System.out.println(a+"/ "+05+"/ "+b);
}
else if(a<=181)
{a=a-151;
System.out.println(a+"/ "+06+"/ "+b);
}
else if(a<=212)
{a=a-181;
System.out.println(a+"/ "+07+"/ "+b);
}
else if(a<=243)
{a=a-212;
System.out.println(a+"/ "+8+"/ "+b);
}
else if(a<=274)
{a=a-243;
System.out.println(a+"/ "+9+"/ "+b);
}
else if(a<=304)
{a=a-274;
System.out.println(a+"/ "+10+"/ "+b);
}
else if(a<=334)
{a=a-304;
System.out.println(a+"/ "+11+"/ "+b);
}
else if(a<=365)
{a=a-334;
System.out.println(a+"/ "+12+"/ "+b);
}
}
}
}