Update Java version references, add note on var usages

CONTRIBUTING.md

@@ -27,12 +27,12 @@ which can be obtained in (most) package managers such as `apt` (Debian / Ubuntu;
 you will most likely use this for WSL), `homebrew` (macOS / Linux), and more:
 
 - `git` (package `git` everywhere);
-- A Java 17 or later JDK (packages vary, use Google/DuckDuckGo/etc.).
+- A Java 21 or later JDK (packages vary, use Google/DuckDuckGo/etc.).
   - [Adoptium](https://adoptium.net/) has builds for most operating systems.
-  - Paper requires JDK 17 to build, however, makes use of Gradle's
+  - Paper requires JDK 21 to build, however, makes use of Gradle's
     [Toolchains](https://docs.gradle.org/current/userguide/toolchains.html)
     feature to allow building with only JRE 11 or later installed. (Gradle will
-    automatically provision JDK 17 for compilation if it cannot find an existing
+    automatically provision JDK 21 for compilation if it cannot find an existing
     install).
 
 If you're on Windows, check
@@ -42,11 +42,11 @@ If you're compiling with Docker, you can use Adoptium's
 [`eclipse-temurin`](https://hub.docker.com/_/eclipse-temurin/) images like so:
 
 ```console
-# docker run -it -v "$(pwd)":/data --rm eclipse-temurin:17.0.1_12-jdk bash
+# docker run -it -v "$(pwd)":/data --rm eclipse-temurin:21.0.3_9-jdk bash
 Pulling image...
 
 root@abcdefg1234:/# javac -version
-javac 17.0.1
+javac 21.0.3
 ```
 
 ## Understanding Patches
@@ -237,6 +237,10 @@ into most IDEs and formatters by default. There are a few notes, however:
 There are exceptions, especially in Spigot-related files
 - When in doubt or the code around your change is in a clearly different style,
 use the same style as the surrounding code.
+- `var` usage is heavily discouraged, as it makes reading patch files a lot harder
+and can lead to confusion during updates due to changed return types. The only
+exception to this is if a line would otherwise be way too long/filled with hard
+to parse generics in a case where the base type itself is already obvious
 
 ### Imports
 When adding new imports to a class in a file not created by the current patch, use the fully qualified class name

patches/server/0322-Improve-java-version-check.patch

@@ -6,7 +6,7 @@ Subject: [PATCH] Improve java version check
 Co-Authored-By: MiniDigger <admin@benndorf.dev>
 
 diff --git a/src/main/java/org/bukkit/craftbukkit/Main.java b/src/main/java/org/bukkit/craftbukkit/Main.java
-index caa7fefab037a24713e9f7f15a541d47bc7655ee..cc4f7f5bdb6b930af4130dc775e4ed754be87783 100644
+index caa7fefab037a24713e9f7f15a541d47bc7655ee..11b1e23ea2a0d4faf7e74d3c9580b7a776ac795b 100644
 --- a/src/main/java/org/bukkit/craftbukkit/Main.java
 +++ b/src/main/java/org/bukkit/craftbukkit/Main.java
 @@ -202,23 +202,27 @@ public class Main {
@@ -24,7 +24,7 @@ index caa7fefab037a24713e9f7f15a541d47bc7655ee..cc4f7f5bdb6b930af4130dc775e4ed75
 -                System.err.println("Unsupported Java detected (" + javaVersion + "). Only up to Java 22 is supported.");
 +            boolean isOldVersion = javaVersion < 61.0;
 +            if (!skip && isOldVersion) {
-+                System.err.println("Unsupported Java detected (" + javaVersion + "). This version of Minecraft requires at least Java 17. Check your Java version with the command 'java -version'. For more info see https://docs.papermc.io/misc/java-install");
++                System.err.println("Unsupported Java detected (" + javaVersion + "). This version of Minecraft requires at least Java 21. Check your Java version with the command 'java -version'. For more info see https://docs.papermc.io/misc/java-install");
                  return;
              }
              String javaVersionName = System.getProperty("java.version");