What is Java ?

Java is a programming language and a platform used for creating software. Java is a multipurpose programming language. 

Java was developed by James Gosling and two others. The first public implementation of java was released in 1996. 

There were five primary goals in the creation of the Java Programming language:

1. It must be Simple, Object-Oriented, and familiar.

2. It must be robust and secure.

3. It must be architecture-neutral and portable.

4. It must execute with high performance.

5. It must be interpreted, threaded, and dynamic.

Why Java is called a platform ?

Java is called as a platform because java is not just a programming language it provides an environment to run java programs. Java runs inside JRE which is an environment.

Types of Application that can be created using Java

Mobile Applications

Software can be developed for mobile devices using Java. Android smartphone applications can be developed using Java with the help of Android Studio software.

Desktop GUI Applications

Desktop Graphical User Interfaces can be created using Java. Java packages like AWT (Abstract Windows Toolkit) and Swing can be used to make GUI applications with the help of Java.

Web Applications

Web applications can also be made usnig Java. Java has a plenty of web technologies that can be used to create applications that run of the web.

Some of the technologies are as follows :

    Java Servet API

    JavaServer Pages (JSP)

    JavaServer Faces Technology

    JDBC API   (source)