Java inheritance, using builder pattern

Question

I have 3 classes:

1. Error
2. ShellError
3. WebError

where

ShellError extends Error 

and

WebError extends Error

In ShellError there are fields some of which are optional and others are required. I am building the object in the following manner:

shellError = new ShellError.Builder().setFile(filePattern)
.setHost(host).setPath(path).setSource(file.isSource())
.setJobName(p.getJobName()).build();

Since ShellError extends Error, I further:

shellError.setDescription(msg.toString());
shellError.setExceptionClass("MyEvilException");
shellError.setExceptionMessage("Some clever error message");
shellError.setStacktrace(stack);

So ... why bother with Builder? I like the fact that my build() amongst other things conveniently validates that all fields are set appropriately etc.

I would love it if I could .. build() ShellError and add to it the fields from the Error class.

What i did works.

• The question is:

Is there a better way, or does it make sense what I did?

-- EDIT

I updated Builder() to accept some of the parameters which were in Error class before. Now I have

shellError = new ShellError.Builder(exception, "Some description").setFile(filePattern).setHost(host)
.setPath(path).setSource(file.isSource()).
setJobName(p.getJobName()).build();

What do you say? Better? Worse?

Answer 1

The builder pattern, popularized by Josh Bloch, has several benefits, but it doesn't work so elegantly on parent/subclasses, as explained in this discussion by our colleagues in the C# world. The best solution I have seen so far is this one (or a slight variant of it).