String a = "//aaa";
        System.out.println(a);
        Pattern pa = Pattern.compile("^(//)([a-zA-Z]+)");
        Matcher ma = pa.matcher(a);
        if(ma.find())
            System.out.println(ma.group(2));

------解决方案--------------------
String pattern="[\w]*";
这个是不是就可以啊

------解决方案--------------------
Java code

        String a = "//aaa";
    String b = "/bbb";
    String c = "ccc";
        Pattern pa = Pattern.compile("^[^([/]{2})]([a-zA-Z]+)");
        Matcher ma = pa.matcher(a);
        Matcher mb = pa.matcher(b);
        Matcher mc = pa.matcher(c);
        if(ma.find())
            System.out.println("ma="+ma.group());
        if(mb.find())
            System.out.println("mb="+mb.group());
        if(mc.find())
            System.out.println("mc="+mc.group());