e081. determining if a string is a legal java identifier.txt

这里面包含了一百多个JAVA源文件

Briefly, a valid Java identifier must start with a Unicode letter, underscore, or dollar sign ($). The other characters, if any, can be a Unicode letter, underscore, dollar sign, or digit. 
For more details, see http://java.sun.com/docs/books/jls/second_edition/html/lexical.doc.html. 

    // Returns true if s is a legal Java identifier.
    public static boolean isJavaIdentifier(String s) {
        if (s.length() == 0 || !Character.isJavaIdentifierStart(s.charAt(0))) {
            return false;
        }
        for (int i=1; i<s.length(); i++) {
            if (!Character.isJavaIdentifierPart(s.charAt(i))) {
                return false;
            }
        }
        return true;
    }

    // Some examples
    boolean b = isJavaIdentifier("my_var"); // true
    b = isJavaIdentifier("my_var.1");       // false
    b = isJavaIdentifier("$my_var");        // true
    b = isJavaIdentifier("\u0391var");      // true
    b = isJavaIdentifier("_");              // true
    b = isJavaIdentifier("$");              // true
    b = isJavaIdentifier("1$my_var");       // false