I really always hate to see folks being snippy in their answers, I apologize for the answers you got so far.
The core differences are:
Java:
The essential tools for any Java developer, including a Java IDE, a Git client, XML Editor, Mylyn, Maven and Gradle integration
Web/JavaScript:
The essential tools for any JavaScript developer, including JavaScript, TypeScript, HTML, CSS, XML, Yaml, Markdown... languages support; Kubernetes, Angular and React frameworks support; Node.js debugger; Git client; Mylyn task management; integrated terminal and remote filesystem explorer; Web and application server management.
At the end of the day its all about which packages come pre-installed. You can choose to start with one and then add the packages you want from the other. To see which specific pages are installed with either go here:
Java: https://www.eclipse.org/downloads/packages/release/2019-09/r/eclipse-ide-java-developers
Web/JavaScript: https://www.eclipse.org/downloads/packages/release/2019-09/r/eclipse-ide-web-and-javascript-developers-includes-incubating-components