Is this is best practise

Question

Hi,
I have a class called CustomDocument , to which i pass a URL, this will inturn call two methods getW3cDocument and splitDocumentIntoFields, these two methods parse the document and populate the hash map accordingly with necessary values.
I was suggested that that this way of calling a constructor and creating a document object was not good practice, in case there is a parsing error or if some exception occurs , then the constructor might throw an exception half way through constructing the object.
No site that i reffered to gave any such specification with respect to constructors.
Are constructors only to initialize variables. What if in such cases where i want all my fields (hashmap) populated with values , i.e as soon as i create an object , the field contents should be present in the hashmap.
1. Can anyone tell me if this confirms to java best practices?
2. Is it right if constuctors call methods, that will do some processing to initialize valus to say hashmaps in my case?
3. Shouldnt constructors throw exceptions? (half way through creating an object lets say)?
public class CustomDocument
private java.net.URL _url;
private org.w3c.dom.Document _w3cdoc;
private java.util.HashMap<String, Field> _fieldContents;
public CustomDocument(URL url) {
    _url = url;
  // Initializing the field contents
    _fieldContents = new HashMap<String, Field>();
//Get the dom object
    _w3cdoc = getW3cDocument(_url);
//This method will read through the dom object and extract
//information and populate the hashmap _fieldContents
    splitDocumentIntoFields(_w3cdoc);
}Thanks.

Answer 1

2. Is it right if constuctors call methods, that will
do some processing to initialize valus to say
hashmaps in my case?It's fine for a ctor to call methods, but you have to be careful about calling non-final methods on the object being initialized.
import java.util.*;
public class CtorNonFinalMethod {
    public static void main(String[] args) throws Exception {
        new Child();
class Parent {
    int ii;
    Parent() {
        System.out.println("entering parent ctor");
        init();
        System.out.println("leaving parent ctor");
    void init() {
        System.out.println("entering parent init");
        ii = 123;
        System.out.println("leaving parent init");
class Child extends Parent {
    List<String> list = new ArrayList<String>();
    void init() {
        System.out.println("entering child init, list = " + list);
        list.add("abc");
        System.out.println("leaving child init, list = " + list);
entering parent ctor
entering child init, list = null
Exception in thread "main" java.lang.NullPointerException
     at Child.init(CtorNonFinalMethod.java:30)
     at Parent.<init>(CtorNonFinalMethod.java:14)
     at Child.<init>(CtorNonFinalMethod.java:25)
     at CtorNonFinalMethod.main(CtorNonFinalMethod.java:5)