program structure of java

How to use Program Structure of Java

Posted on May 31, 2024
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In this java tutorial, you will learn the essential program structure of the java programming language.

Program Structure

  • Java has six sections of program structure. The details given as below

1. DOCUMENTATION SECTION

  • It is an optional
  • Gives the complete information about program like name of the program, author name, date, version & other details, etc
  • Like c/c++, java supports two comment type statements 
  1. Single Line Comment
  2. Multiline Comments

Single Line Comment

  • It is used to ignore only one statement at a time
  • It starts with operator like //

Example

Multiple Line Comments

  • It is used to ignore more than one statements at a time
  • This is done by using the operator like /* … */

Example

2. USER DEFINED PACKAGE SECTION

  • Here we can create our own package 
  • Package is a set of classes / interfaces
  • It is just like a container

Syntax

              <package> <user-defined name>;

Example

NOTE

  • It is important to note that class name and file name must be the same in java.

3. PREDEFINED PACKAGE SECTION

  • It is an optional
  • It is used to load the predefined java libraries using “import” keyword
  • It is used to create different types of applications, algorithms, tools & OS, etc
  • Ex. java.lang.*, java.io.*, java.util.*, etc

Syntax

              <import> <package.subpackage.*>;

              <import> <package.subpackage.Class>;

Example

              import java.sql.*; // load all classes from sql package

              import java.io.*; // load all classes from io package 

              import java.io.DataInputStream; // load only specific class

import

  • It is a reserved keyword in java
  • It is mainly used to load the system packages in java.

4. INTERFACES 

  • It has only declaration, no body (no definition)
  • All the methods in the interfaces are public by default
  • All the variables in the interfaces are const by default
  • Interfaces are defined using interface (reserved word)
  • It has no constructor

Syntax

           < interface> <user-defined name>

           {   

                    // variable initialization

                    // method declaration, no definition

           }

Example

NOTE

  • If the subclass inherits the interface, then the sub class must implement the methods of interface, else subclass is also considered as an interface type.

5. CLASSES

  • Collection of variables & methods are grouped together into a single entity (called class) 
  • classes are default or friendly modifier by default
  • All the variables and methods in the class is default modifier by default
  • Classes are defined using class (reserved word)
  • It supports constructors (parameter & parameter less)

Syntax

Example

6. main() METHOD SECTION

  • It is essential part in program
  • It is an entry point of any java program
  • It starts the program execution
  • main() method accepts only void and int type. Other types are not allowed. 

Example

NOTE

  • It is an important to note that, main() method does not return any type except void (It does not return any value)
  • Main() method must be void type.

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