Introduction to Objects - Advanced Topics in Java: Core Concepts in Data Structures - page 33

private String author = "No Author";
private String title;
private double price;
private int pages;
private char binding = 'P'; // for paperback
private boolean inStock = true;
}

Now, when an object is created, author , binding , and inStock will be set to the specified values while title ,
price , and pages will assume the default values. A variable is given a default value only if no explicit value is assigned
to it. Suppose we create an object b with this:

Book b = new Book();

The fields will be initialized as follows:

•

author is set to "No Author" . // specified in the declaration

•

title is set to null . // default for ( String ) object type

•

price is set to 0.0 . // default for numeric type

•

pages is set to 0 . // default for numeric type

•

binding is set to 'P' . // specified in the declaration

•

inStock is set to true . // specified in the declaration

2.3 Constructors
Constructors provide more flexible ways of initializing the state of an object when it is created. In the following
statement, Book() is termed a constructor :

Book b = new Book();

It is similar to a method call. But, you might say, we did not write any such method in our class definition. True,
but in such cases, Java provides a default constructor —one with no arguments (also called a no-arg constructor). The
default constructor is quite simplistic; it just sets the values of the instance variables to their default initial values.
Later, we could assign more meaningful values to the object's fields, as in the following:

b.author = "Noel Kalicharan";
b.title = "DigitalMath";
b.price = 29.95;
b.pages = 200;
b.binding = 'P'; //for paperback
b.inStock = true; //stock is available

Now suppose that when we create a book object, we want Java to assign the author and title automatically.
We want to be able to use statements such as the following for creating new book objects:

Book b = new Book("Noel Kalicharan", "DigitalMath");