java double四舍五入两位小数

public static void main(String[] args){   

 int a=11;

 int b=3;

 System.out.println((double)a/b);

 DecimalFormat df = new DecimalFormat("#.00");   

  System.out.println(df.format((double)a/b));  

  System.out.println(Math.round((double)a/b)); 

 }