Java is a general purpose, class-based, object-oriented programming language designed for having lesser implementation dependencies. It is computing platform for application development. It is fast, secure, and reliable, therefore. It is widely used for developing Java applications in laptops, data centers, game consoles, scientific supercomputers, cell phones, etc.
Java Platform is a collection of programs that help programmers to develop and run Java programming applications efficiently. It includes an execution engine, a compiler, and a set of libraries in it. It is a set of computer software and specifications. James Gosling developed the Java platform at Sun Microsystems, and the Oracle Corporation later acquired it.
Java is among the most popular programming languages out there, mainly because of how versatile and compatible it is. Java can be used for a large number of things, including software development, mobile applications, and large systems development. As of 2019, 88% market share of all smartphones run on Android, the mobile operating system written in Java. Knowing Java opens a great deal of doors for you as a developer.
Standalone applications are the application which runs on separate computer process without adding any file processes. The standalone application is also known as Java GUI Applications or Desktop Applications which uses some standard GUI components such as AWT(Abstract Windowing Toolkit), swing and JavaFX and this component are deployed to the desktop. These components have buttons, menu, tables, GUI widget toolkit, 3D graphics etc. using this component a traditional software is developed which can be installed in every machine.
Example: Media player, Antivirus, Paint, POS Billing software, etc.
Web Applications are the client - server software application which is run by the client. Servlets, Struts, JSP, Spring, hibernate etc. are used for the development of a client-server application eCommerce application is also developed in java using eCommerce platform i.e Broadleaf.
Example: mail, e-commerce website, bank website etc.
Enterprise application is middleware applications. To use software and hardware systems technologies and services across the enterprises. It is designed for the corporate area such as banking business systems.
Example: e-commerce, accounting, banking information systems etc.
For mobile applications, Java uses ME or J2ME framework. This framework are the cross platform that runs applications across phones and smartphones. Java provides a platform for application development in Android too.
Example: WhatsApp, Xender etc.
For running Java in your system you need to download & install JDK Kit From Here (recommended Java Version is Java 11 but you can download Java 13 or Java 14).