Java wasn't a revolution even at the time it first appeared. It introduced little that was new and yet we were carried along on a wave of enthusiasm. I can remember wondering why anyone would use it when there was Visual Basic and C++ to use. Java took the syntax of C and C++ and added it to the idea of a virtual machine as typified at the type by the UCSD P machines. Was it a killer blend of features?

When it started out as a project, at Sun Microsystems, to produce a better C++ the target of the language was what we might call the IoT (Internet of Things) today. Yes, even 25 years ago people were hyping the IoT. Sun had hopes of cashing in on the coming boom in small appliances and you need to keep in mind that Sun was a hardware manufacturer. Interestingly the team, James Gosling, Mike Sheridan, Patrick Naughton and others, considered basing their work on C++, but they rejected it for reasons that we would still consider valid today - easy to make errors, no garbage collection, memory hungry and so on. 

James Gosling has a Phd in computer science from Carnegie Mellon and he is generally credited with inventing Java

At first no one was interested in the programming language,  naked Oak after the tree that was just outside Gosling's office, much at all. The early days of any language are difficult but the proto-Java seems to have been much unloved. Then someone had a really good idea suggesting that the then-new World Wide Web might just be something worth considering.

The language was renamed, Java, after Oak Technology raised a legal challenge and the language was used to implement a web browser - HotJava. The way that the Java name allowed coffee related names to be used for thing probably really did contribute to its popularity.

Strictly speaking, although Java 1.0 could be downloaded in 1994, the public release Java 1.0a2, happened at the SunWorld conference on May 23 1995. At the same time Netscape announced that its browsers would support Java. Also at about the same time Brendan Eich developed a language to run in the browser called Mocha - but the name wasn't coffee-oriented enough and so it was renamed JavaScript, even though it has nothing at all to do with Java.

Perhaps the great achievement of Java was the introduction of coffee-oriented programming.

Java Applets

Java entered the browser by way of the Applet and for once programmers who knew little about the web or the intenet could create graphics and games that ran in web pages. For a while Java was the only way of doing anything impressive in a web page - and believe me even simple games and seeing a chart drawn before your very eyes was impressive, these really were simpler times. If you saw it your immediate reaction was to ask "how is this witchcraft achieved?" Of course, the answer was Java and it rapidly became the must-have language.

The irony is that today plug-ins like the Applet are thought of as the worst thing in the world and browser-side Java is not a big thing. It still exists and there are financial institutions that still insist you have Java applet support switched on. In this sense client-side Java has become the Cobol of the 90s.

Outside of the browser Java never really caught on apart from a few exceptions. One of the reasons was that it never managed to settle on a good GUI framework. AWT was the first, but it didn't look good. It was replaced/extended by the Swing library. which was much better. Then it was superseded by Java FX, which arguably few got to understand or use. Today, Java desktop programmers often find it hard to pick a presentation layer.

The interest in Java on the client-side allowed it to spread into the server-side and line of business applications. Java was at that time the only popular object-oriented language that seemed to be "serious" enough for the task. Because if its use of a virtual machine - the Java Virtual Machine or JVM - it also was easy to port to other environments. Java wasn't the first language to promise Write Once Run Anywhere (WORA) but it was the first language that looks solid enough to do it. However, the downside was that Java was slow. Back in those early days, development environments for Java were simply too slow for the job.