Structure of Java Program

A Java program involves the following sections:

Documentation
Section

The documentation section is an important section
but optional for a Java program. It includes basic information about
a Java program. The information includes the author's name, date of
creation, version, program name, company name, and description of
the program.

It improves the readability of the program. Whatever
the documentation section contains, the Java compiler ignores the statements
during the execution of the program.

To write the statements in the documentation
section, we use comments. The comments may be single-line,
multi-line, and documentation comments.

• Single-line
  Comment: It starts with a pair of forwarding slash (//). For
  example:

//First Java Program  

• Multi-line
  Comment: It starts with a /* and ends with */. We
  write between these two symbols. For example:

/*It is an example of 

multiline comment*/  

• Documentation Comment: It starts with the delimiter (/**) and ends
  with */. For example:

/**It is an example of documentation comment*/  

Package
Declaration

The package declaration is optional. It is placed just after the
documentation section. The package name in which the class is placed
is declared in this section. There can be only one package statement
in a Java program. It must be defined before any class and interface
declaration. The keyword “package” is used to declare the package
name.

For example:

package Mypackage;

Import
Statements

The package contains the many predefined classes and interfaces. If any
class of a particular package is to be used, that class has to be imported.

The import statement represents the class stored in the other package. The “import” keyword
is used to import the class. It is written before the class declaration and
after the package statement. The import statement is used in two ways, either
import a specific class or import all classes of a particular package. In a
Java program, we can use multiple import statements.

For example:

1. import java.util.Scanner; //it imports the Scanner class only  


2. import java.util.*; //it imports all the class of the java.util package  

Interface
Section

It is an optional section. An interface can be created in
this section if required. The “interface” keyword is used to
create an interface. An interface is a slightly different from the
class.

It contains only constants and method declarations.
Another difference is that it cannot be instantiated. An interface can be used in
classes by using the “implements” keyword. An interface can
also be used with other interfaces by using the “extends” keyword.

Class Definition

It is vital part of a Java program. A Java program may
conation more than one class definition. The “class” keyword is
used to define the class. The class is a blueprint of a Java program. It
contains information about user-defined methods, variables, and constants.
Every Java program has at least one class that contains the main() method.

class Student //class definition  

{  

}  

Class Variables
and Constants

In this section, variables and constants that are
to be used later in the program are defined. In a Java program, the variables
and constants are defined just after the class definition. The variables and
constants store values of the parameters. It is used during the execution of
the program.

class Student //class definition  

{  

String sname;  //variable  

int id;   

double percentage;   

}  

Main Method
Class

In this section, the main() method is defined. It
is essential for all Java programs. Because the execution of all Java programs
starts from the main() method.

In other words, it is an entry point of the class. It must be inside the
class. Inside the main method, we create objects and call the methods.

public class Student //class definition  

{  

public static void main(String args[])  

{  

//statements  

}  

}  

Methods and
behavior

In this section, the functionality of the program is defined by using
the methods. The methods are the set of instructions that we want to
perform. These instructions execute at runtime and perform the specified task.

public class Demo //class definition  

{  

public static void main(String args[])  

{  

void display()  //method

{  

System.out.println("Welcome to javaclass");  

}  

//statements  

}  

}