Constructors and object creation

A constructor initializes an object's state. It has the same name as its class and no return type. Constructors may be no-argument, parameterized, or overloaded; if no constructor is declared, Java supplies a default no-argument constructor.

class Book {
    String title;
    Book(String title) { this.title = title; }
}
Book b = new Book("Networks");

new allocates an object, initializes its fields to default values, and invokes the selected constructor. this(...) calls another constructor in the same class and must be first; super(...) calls a superclass constructor and must also be first.