try
Calendar c = Calendar.getInstance(); // this takes current date
c.set(Calendar.DAY_OF_MONTH, 1);
System.out.println(c.getTime()); // this returns java.util.Date
Updated (Since Java 8):
import java.time.LocalDate;
LocalDate todaydate = LocalDate.now();
System.out.println("Months first date in yyyy-mm-dd: " +todaydate.withDayOfMonth(1));