Question

I have two classes Parent and Child.

class Child extends Parent {
    private String extraField1;
    private String extraField2;
    ...
}

Child class has 2 extra fields extraField1 and extraField2.

Q1. Should I make two diff. tables in the databse: one for Child and other for Parent?

or

Q1. Should I add two columns in the Parent table (each column for one extra field) and store the Child in the Parent table.

=============================== EDITED =======================================

Yes, Child and Parent are classes in the same hierarchy.

Answer 1

Should there be 2 datatables for a Parent and Child class in Java?

There is no universal answer to this question. There are actually several techniques to map an inheritance hierarchy into a relational database and they all have advantages and disadvantages. Choosing one or the other depends on your context.

Scott Ambler details the various approaches in the section 2. Mapping Inheritance Structures of his famous paper Mapping Objects to Relational Databases: O/R Mapping In Detail that I’m quoting below:

(…) In this
section you’ll see that there are
three primary solutions for mapping
inheritance into a relational
database, and a fourth supplementary
technique that goes beyond inheritance
mapping. These techniques are:

• Map the entire class hierarchy to a single table
• Map each concrete class to its own table
• Map each class to its own table
• Map the classes into a generic table structure

For a full comparison (with advantages, disadvantages and a recommendation on when to use), have a look at the section 2.6 Comparing The Strategies.

I can’t do a better job than him so there is no point at paraphrasing him, just refer to the original paper.