structure of a Java program:

Java Program Structure: A Java program may contain many classes of which only one class defines a main method. Classes contain data members and methods that operate on the data members of the class. Methods may contain data type declarations and executable statements. To write a Java program, we first define classes and then put them together. A Java program may contain one or more sections as shown below:

Documentation Section	Suggested
Package Statement	Optional
Import Statements	Optional
Interface Statements	Optional
Class Definitions	Optional
main Method Class { Main Method Definition }	Essential

Documentation Section: The documentation section comprises a set of comment lines giving the name of the program, the author and other details. Comments explain why and what of classes and how of algorithms. This would greatly help in maintaining the program. Java uses a new style of comment /**....*/ known as documentation comment. This form of comment is used for generating documentation automatically.

Package Statement: The first statement allowed in a Java file is a package statement. This statement declares a package name and informs the compiler that the classes defined here belong to this package. Example:

package student;

The package statement is optional. That is, our classes do not have to be part of package.

Import Statements: The next thing after a package statement (but before any class definitions) may be a number of import statements. This is similar to the include statement in C. Example:

import student.test;

This statement instructs the interpreter to load the test class contained in the package student. Using import statements, we can have access to classes that are part of other named packages.

Interface Statements: An interface is like a class but includes a group of method declarations. This is also an optional section and is used only when we wish to implement the multiple inheritance features in the program.

Class Definitions: A Java program may contain multiple class definitions. Classes are the primary and essential elements of a Java program. These classes are used to map the objects of real-world problems. The number of classes used depends on the complexity of the problem.

Main Method Class: Since every Java stand-alone program requires a main method as its starting point, this class is the essential part of a Java program. A simple Java program may contain only this part. The main method creates objects of various classes and establishes communications between them. On reaching the end of main, the program gets terminated.