How much work should the constructor for an HTML p

Question

How much work is it reasonable for an object constructor to do? Should it simply initialize fields and not actually perform any operations on data, or is it okay to have it perform some analysis?

Background: I was writing a class which is responsible for parsing an HTML page and returning various information based on the parsed information. The design of the class is such that the class' constructor does the parsing, throwing an exception if an error occurs. Once the instance is initialized, the parsed values are available without further processing via accessors. Something like:

public class Parser {

    public Parser(final String html) throws ParsingException {
        /* Parsing logic that sets private fields */
        /* that throws an error if something is erroneous.*/
    }

    public int getNumOfWhatevers() { return private field; }
    public String getOtherValue()  { return other private field; }
}

After designing the class I started to wonder if this was correct OO practice. Should the parsing code be placed within a void parseHtml() method and the accessors only return valid values once this method is called? I feel as though my implementation is correct, but I can't help but feel that some OO purists might find it incorrect for some reason and that an implementation such as the following would be better:

public class Parser {

    public Parser(final String html) {
        /* Remember html for later parsing. */
    }

    public void parseHtml() throws ParsingException { 
        /* Parsing logic that sets private fields */
        /* that throws an error if something is erroneous.*/
    }

    public int getNumOfWhatevers() { return private field; }
    public String getOtherValue()  { return other private field; }
}

Are there instances where initialization code, such as parsing information, should not occur within the constructor, or am I just being silly and second-guessing myself?

What are the benefits/drawbacks of splitting the parsing from the constructor?

Thoughts? Insights?

Answer 1

I'd probably just pass enough to initialize the object and then have a 'parse' method. The idea is that expensive operations should be as obvious as possible.