Try like this:
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
Date c= sdf.parse("2015-05-26");
String date=sdf.format(c);
System.out.println(date);
To format the current date in yyyy-MM-dd format you can try like this
Date date = new Date();
String str = new SimpleDateFormat("yyyy-MM-dd").format(date);
Kindly refer SimpleDateFormat