I want to install Java, in KaOs, but when I was looking through Internet...
You certainly did not look at the one place relevant to this distribution, the KaOS website. If you had looked you would have seen that KaOS is complete independent, not based on any:
https://kaosx.us/
If you looked at:
https://kaosx.us/about/toolkits/
You would have seen there are no repositories to add, there are three only.
If you had read:
https://kaosx.us/about/based/
You'd know not to look outside of KaOS for repositories.
If you looked at:
https://kaosx.us/docs/pacman/
You would have known how to search the repos (or use the search options in Octopi).
pacman -Ss java
main/antlr2 2.7.7-2
ANother Tool for Language Recognition, (formerly PCCTS) is a language tool that provides a framework for constructing recognizers,
compilers, and translators from grammatical descriptions containing C++ or Java actions
main/apache-ant 1.9.7-1
A java-based build tool.
main/astyle 2.05.1-1
Artistic Style is a source code indenter, formatter, and beautifier for the C, C++, C# and Java programming languages.
main/beanshell 2.1.8-1
Small, source level Java interpreter with object based scripting language features written in Java
main/ca-certificates-java 20121112+nmu2-2
Common CA certificates (JKS keystore)
main/doxygen 1.8.11-1
A documentation system for C++, C, Java, IDL and PHP
main/eclipse-ecj 4.4-1
Eclipse java bytecode compiler
main/fastjar 0.98-2
Sun java jar compatible archiver
main/geos 3.5.0-1
A C++ port of the Java Topology Suite
main/hamcrest 1.3-2
Java matcher objects library
main/json-glib 1.2.0-1
Library providing serialization and deserialization support for the JavaScript Object Notation format
main/junit 4.12-1
Automated testing framework for Java
main/openjdk 7u99_b00_2.6.5-1
An open-source implementation of the seventh edition of the Java SE Platform.
main/openjdk-src 7u99_b00_2.6.5-1
An open-source implementation of the seventh edition of the Java SE Platform. (Source package)
main/python2-antlr2 2.7.7-2
ANother Tool for Language Recognition, (formerly PCCTS) is a language tool that provides a framework for constructing recognizers,
compilers, and translators from grammatical descriptions containing C++ or Java actions (Python version)
main/qt5-canvas3d 5.7.0-1 (qt5)
JavaScript 3D rendering API for Qt Quick
main/qt5-webchannel 5.7.0-1 (qt5) [installed: 5.7.0-3]
Module being used in e.g. Qt WebKit to provide a seamless integration of QML/C++ QObjects into JavaScript clients
main/rhino 1.7R4-2
Open-source implementation of JavaScript written entirely in Java
apps/eclipse 4.6-1
An IDE for Java and other languages
apps/icedtea-web 1.6.2-1 (network)
Provides a Free Software web browser plugin running applets written in the Java programming language and an implementation of Java Web
Start, originally based on the NetX project.
apps/jdk 8.92-1
Java Development Kit
apps/jitsi 2.8.5426-1
An audio/video SIP VoIP phone and instant messenger written in Java (formerly SIP-Communicator)
apps/js 17.0.0-2 [installed: 17.0.0-4]
JavaScript interpreter and libraries
apps/khtml 5.24.0-1 (kf5) [installed: 5.24.0-3]
Web rendering engine, based on the KParts technology and using KJS for JavaScript support.
apps/luceneplusplus 3.0.7-1
Up to date C++ port of the popular Java Lucene library, a high-performance, full-featured text search engine.
apps/nodejs 6.2.2-1
Platform built on Chrome's JavaScript runtime for easily building fast, scalable network applications.
apps/ragel 6.9-1
Compiles executable finite state machines from regular languages, targeting C, C++, Obj-C, C#, D, Java, Go and Ruby.
apps/scala 2.11.8-1
Acronym for Scalable Language, running on the JVM. Java and Scala classes
If you had looked at:
https://kaosx.us/docs/package/
You would have learned how to add, build & maintain packages not in the (limited) KaOS repos.
No idea what "java" package you are looking for.
But it looks like you might be on the complete wrong distribution, if you are looking for Arch or an Arch derivative, install any of those, KaOS is not among them.