如何将 AdoptOpenJDK 8 和 11 与 Oracle JDK 8 并行安装并与 Eclipse 一起使用

Question

I'm trying to update Java to Version 11, but don't want to use Oracles JDK because of the license. I also would like to install and use AdoptOpenJDK 8 because of that. My OS is Windows 10.

I've already tried to install AdoptOpenJDK 11 without overwriting any settings, as I want other java-programs to still run using Oracles JRE 8. I added the AdoptOpenJDK installation folder to the installed JREs in eclipse and when I ran some test code, "java.version" was set to 11.0.7, but when trying the new 'var' feature, Eclipse said that 'var' is not allowed here . I changed the compiler compliance level to 11 and updated to Eclipse Version 2020-03 (4.15.0), but it still didn't work.
Then I reinstalled AdoptOpenJDK 11 and let the installer change all the settings, but it still wouldn't work.

How can I install AdoptOpenJDK 8 and 11 parallel to OracleJDK 8 on my system and set in Eclipse which one to use per project?

EDIT: Ok, it works now, apparently I just didn't understand how to use 'var' correctly. Thank you for your help nonetheless.

Answer 1

The error message 'var' is not allowed here means that you are using Java 10 or higher, but var is used somewhere in the code where you cannot . Otherwise, for a compiler compliance level lower than 10, you would get var cannot be resolved to a type .

Example:

class Sample {

    var s = ""; // 'var' is not allowed here

    var foo() { // 'var' is not allowed here
        // ...
    }

    void foo(var x) { // 'var' is not allowed here
        // ...

        var s = ""; // okay

    }

}