Servlet Post parameters : what case can a parameter have several values?

Here is the a function on my servlet to test various things (I'm new to servlets althought I understadn the logic)

 public void testParameters(HttpServletRequest request, HttpServletResponse response) throws IOException{
  PrintWriter out = response.getWriter();
  Enumeration paramN开发者_运维问答ames = request.getParameterNames();
  while(paramNames.hasMoreElements()) {
   String paramName = (String)paramNames.nextElement();
   out.println("\n>>>" + paramName);

   String[] paramValues = request.getParameterValues(paramName);
   if (paramValues.length == 1) {
    String paramValue = paramValues[0];
    if (paramValue.length() == 0){
     out.print("No Value");
    }else{
     out.print(paramValue);
    }
   } else {
    System.out.println("Number of parameters "+paramValues.length);
    for(int i=0; i<paramValues.length; i++) {
     out.print("" + paramValues[i]);
    }
   }
  }
 }

(this code I took from a tutorial and tweeked so it might just be something stupid)

I get everything working just fine but I was wandering in what cases does a parameter have several values?

Example: http://myhost/path?a=b&a=c&a=d
The parameter a has values b, c and d.

Example:

<form name="checkform" method="post" action="xxxxx"> 
        Which langauge do you want to learn：<br> 
        <input type="checkbox" name="langtype" value="JSP">JSP
        <input type="checkbox" name="langtype" value="PHP">PHP
        <input type="checkbox" name="langtype" value="PERL">PERL
        <input type="submit" name="b1" value="submit"> 
</form>

The form can allow you to select multiple values. If you ticks all check boxes , then the parameter langtype will have the values JSP , PHP and PERL