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Structure of Java Program: A Comprehensive Guide

Java is an object-oriented programming language used in various fields, such as web development, software development, Android development, and so on. In the article, we will see the structure of the Java program in detail. At the end of this section, you will be able to develop the Hello World Program in Java easily. Let’s dive deep into this article.

Documentation Section

The documentation section is an important section in the Structure of the Java Program. It includes basic information about the Java program. However, it is also optional, which means you can omit it from the Java program.  The information includes the author’s name, date of creation, version program name, company name, and description. It improves the readability of the program. Java compiler ignores them during the program execution. This information is ignored by the compiler because the developer used comments.

Comments are non-executable parts of a program. A compiler does not execute comments in a Java program. It is used for the readability of the source code.

Writing good comments is good practice for developers. There are different types of comments: single-line, multi-line, and documentation comments.

• Single-Line Comment: This comment starts with the “//” and represents a single line of comment
  in the Java program.

//Single-line comment

• Multi-line Comment: This comment starts from the “/* “ and ends with “*/” and is used when more
  than one line has to be enclosed as comments in the Java program.

/* Multiline comment

in Java */

• Documentation Comment: This comment starts with “/**” and with “*/”.

Also Read: Array in Java

Package Declaration

The package declaration in Java’s structure is optional. It comes after the documentation section. We declared the package name in which the class is placed. Note that there can be only one package statement in a Java program. It must be defined before any class and interface declaration. This is necessary because a Java class can be placed in different packages and directories based on the module.

The following program snippet shows how we can define packages in the Java program.

Program

Import Statements

The import statements are used to import classes, interfaces, or Venus stored in the Java program’s different packages. We need to mention which package we are using at the beginning of the program using the import keyword. We either import the entire package or a specific class from that package.

The following program demonstrates “How to import a package in a Java Program”.

Program

Also read: Inheritance in Java

Interface Section

It is an optional section in the Java Structure Program. We can create an interface using the interface keyword. An interface is slightly different from a class. An interface only contains constants and method declarations. There is one more difference between an interface and a class interface that cannot be instantiated.

The following program demonstrates the interface sections.

Program 

Class Definition

This is the mandatory section in the Java Program’s structure. Each program must be written inside a Java class. It is one of the main principles of object-oriented programming that Java strictly follows. It strictly follows Encapsulations.

There can be multiple classes in a single Java Program. The following program demonstrates the structure Java class

Program

Identifiers are used to name classes, methods, and variables. Identifiers can be sequences of uppercase and lowercase characters. It can be a sequence of uppercase and lowercase characters. Identifiers also contain an underscore and ‘$” dollar sign. It should not have digits (0-9) and not contain any special characters.

Variables are also identifiers. It is used for storing the data into a variable of the same type.

Syntax 

Program 

Rules for Naming Variables

Variables have some rules before defining them. Let’s understand one by one.

• Java variables may contain characters, digits and underscores.
• The underscore can be used in between the characters.
• Variable names must be meaningful and depict the program’s logic.
• Variable names should not start with a digit or a special character in Programming.

Main Method Class

The Main method in the Java class is a compulsory part of the program’s structure. It is the compiler’s entry point, where the execution starts. The Java Virtual Machine, or JVM, invokes it.

The main method() is always defined inside a class. This method can call other functions and create objects using this method.

Syntax of the Main Method 

Methods and Behaviours

In this section, we will define the Methods and Behavior by using the methods.  Methods is a collection of statements that perform a specific task. It provides the reusability of code as we write a method once and use it many times by invoking the method.

The following program demonstrates the Methods and Behaviours:

Program 

Output 

Conclusion

In this article, we have discussed all the crucial parts present in any Java program structure. Java is an OOP (Object-Oriented Programming) language. It is very independent and uses both a compiler and an interpreter. This language was released in May 1995 by James Gosling at Sun Microsystems. Understanding the structure of a Java program is essential for any developer to create an efficient program.