如何修改使得Java写txt不覆盖呢

怎么修改使得Java写txt不覆盖呢

Java code

try{              FileWriter fw = new FileWriter("hello.txt");                  String s =  url+"(on page " + base + ")\n";        fw.write(s,0,s.length());       fw.flush();      }     catch(Exception e)     {e.printStackTrace();}