To use the "java" command-line tool you need to install a JDK

like the title says this warning pops up every time i try use a java command line, even though ive installed the x64 RPM Package of SDK already!, theres no errors when i install it but it still asks me to install an SDK, i dont know what to do. Now my macbook air has macOS 10 Mojave 10.14.6 and it has an intel chip.

i wanna know if this problem of the SDK seemingly not installing is because im using a very old macOS, or what, and if upgrading would fix the problem or if im just installing everything wrong