First Program in Java | Core Java Tutorials
This Core Java Tutorials you are able to learn”How to write First Program in Java? ” clearly explains how to write simple java program using java language syntactical rules and clearly explains all the parts of java program.
First Java application:
- Java programming language is case sensitive.
- Look at the capital letters in the following program.
- Some of the Naming conventions (discussion later) we need to follow to write programs.
- Java Application is a collection of Classes.
- Class represents Object.
- We are defining objects in Application to communication using classes.
- Every java instruction must belongs to class.
Class Identity: (FirstApplication)
- Every application is a set of class files.
- Hence every class should be uniquely identified by JVM.
- JVM executes a specific class using its identity only.
Why java class name starts with capital letter ?
- Java API is a set of classes.
- All these classes follow a naming convention rule “CAMEL CASE WITH NO SPACE”.
- In case of pre-defined class, we must follow this rule.
- In case of user defined class, naming convention rule is optional(but recommended).
- We have to face problems if we violate the convention rules while writing application.
- To use the functionality of these classes, first we have to study API.
- Description of these classes will not be available along with JDK installation.
- Oracle Company provided documentation about these classes as an OFFICIAL WEBSITE
- Every java developer should maintain this documentation to develop java applications.
- Instead of searching the documents online, free downloads available for basic java developers.
- Instead of maintain data connection (internet) we can go for website downloads.
Why main method is public & static?
- Main method is the common(static) starting point of all(public) the applications.
- Hence it is public static.
Why main method return type is void?
- JVM invokes main() method to start application execution.
- main() method is not returning anything to JVM, Hence it is void.
- Method naming convention “MIXED CASE & NO SPACE”
- Examples :
- In case of pre-defined methods, we must follow convention rules.
- In case of user-defined methods, these rules are optional(but recommended to follow)
Signature of main method:
- List of arguments is called signature.
- Generally all the programs in a computer execute in OS environment(DOS).
- It is just like C and C++ command line arguments process concept only.
- We will discuss about “Command line arguments” later.