I recently updated my java version to jdk 16.0.1 from jre8u291 for some reason. It seemed that unforged client works well with the  jdk, but forged client failed to start.

Here is the log:(HMCL dev-3.3.184)

Command: "C:\\Program Files\\Java\\jdk-16.0.1\\bin\\java.exe" -Dminecraft.client.jar=.minecraft\versions\1.16.5\1.16.5.jar -XX:+UnlockExperimentalVMOptions -XX:+UseG1GC -XX:G1NewSizePercent=20 -XX:G1ReservePercent=20 -XX:MaxGCPauseMillis=50 -XX:G1HeapRegionSize=16M -XX:-UseAdaptiveSizePolicy -XX:-OmitStackTraceInFastThrow -Xmn128m -Xmx10240m -Dfml.ignoreInvalidMinecraftCertificates=true -Dfml.ignorePatchDiscrepancies=true -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Djava.library.path=D:\MC\.minecraft\versions\1.16.5-forge-36.1.16\natives -Dminecraft.launcher.brand=HMCL -Dminecraft.launcher.version=3.3.184 -cp D:\MC\.minecraft\libraries\net\minecraftforge\forge\1.16.5-36.1.16\forge-1.16.5-36.1.16.jar;D:\MC\.minecraft\libraries\org\ow2\asm\asm\9.0\asm-9.0.jar;D:\MC\.minecraft\libraries\org\ow2\asm\asm-commons\9.0\asm-commons-9.0.jar;D:\MC\.minecraft\libraries\org\ow2\asm\asm-tree\9.0\asm-tree-9.0.jar;D:\MC\.minecraft\libraries\org\ow2\asm\asm-util\9.0\asm-util-9.0.jar;D:\MC\.minecraft\libraries\org\ow2\asm\asm-analysis\9.0\asm-analysis-9.0.jar;D:\MC\.minecraft\libraries\cpw\mods\modlauncher\8.0.9\modlauncher-8.0.9.jar;D:\MC\.minecraft\libraries\cpw\mods\grossjava9hacks\1.3.3\grossjava9hacks-1.3.3.jar;D:\MC\.minecraft\libraries\net\minecraftforge\accesstransformers\3.0.1\accesstransformers-3.0.1.jar;D:\MC\.minecraft\libraries\org\antlr\antlr4-runtime\4.9.1\antlr4-runtime-4.9.1.jar;D:\MC\.minecraft\libraries\net\minecraftforge\eventbus\4.0.0\eventbus-4.0.0.jar;D:\MC\.minecraft\libraries\net\minecraftforge\forgespi\3.2.0\forgespi-3.2.0.jar;D:\MC\.minecraft\libraries\net\minecraftforge\coremods\4.0.6\coremods-4.0.6.jar;D:\MC\.minecraft\libraries\net\minecraftforge\unsafe\0.2.0\unsafe-0.2.0.jar;D:\MC\.minecraft\libraries\com\electronwill\night-config\core\3.6.3\core-3.6.3.jar;D:\MC\.minecraft\libraries\com\electronwill\night-config\toml\3.6.3\toml-3.6.3.jar;D:\MC\.minecraft\libraries\org\jline\jline\3.12.1\jline-3.12.1.jar;D:\MC\.minecraft\libraries\org\apache\maven\maven-artifact\3.6.3\maven-artifact-3.6.3.jar;D:\MC\.minecraft\libraries\net\jodah\typetools\0.8.3\typetools-0.8.3.jar;D:\MC\.minecraft\libraries\org\apache\logging\log4j\log4j-api\2.11.2\log4j-api-2.11.2.jar;D:\MC\.minecraft\libraries\org\apache\logging\log4j\log4j-core\2.11.2\log4j-core-2.11.2.jar;D:\MC\.minecraft\libraries\net\minecrell\terminalconsoleappender\1.2.0\terminalconsoleappender-1.2.0.jar;D:\MC\.minecraft\libraries\net\sf\jopt-simple\jopt-simple\5.0.4\jopt-simple-5.0.4.jar;D:\MC\.minecraft\libraries\org\spongepowered\mixin\0.8.2\mixin-0.8.2.jar;D:\MC\.minecraft\libraries\net\minecraftforge\nashorn-core-compat\15.1.1.1\nashorn-core-compat-15.1.1.1.jar;D:\MC\.minecraft\libraries\com\mojang\patchy\1.1\patchy-1.1.jar;D:\MC\.minecraft\libraries\oshi-project\oshi-core\1.1\oshi-core-1.1.jar;D:\MC\.minecraft\libraries\net\java\dev\jna\jna\4.4.0\jna-4.4.0.jar;D:\MC\.minecraft\libraries\net\java\dev\jna\platform\3.4.0\platform-3.4.0.jar;D:\MC\.minecraft\libraries\com\ibm\icu\icu4j\66.1\icu4j-66.1.jar;D:\MC\.minecraft\libraries\com\mojang\javabridge\1.0.22\javabridge-1.0.22.jar;D:\MC\.minecraft\libraries\io\netty\netty-all\4.1.25.Final\netty-all-4.1.25.Final.jar;D:\MC\.minecraft\libraries\com\google\guava\guava\21.0\guava-21.0.jar;D:\MC\.minecraft\libraries\org\apache\commons\commons-lang3\3.5\commons-lang3-3.5.jar;D:\MC\.minecraft\libraries\commons-io\commons-io\2.5\commons-io-2.5.jar;D:\MC\.minecraft\libraries\commons-codec\commons-codec\1.10\commons-codec-1.10.jar;D:\MC\.minecraft\libraries\net\java\jinput\jinput\2.0.5\jinput-2.0.5.jar;D:\MC\.minecraft\libraries\net\java\jutils\jutils\1.0.0\jutils-1.0.0.jar;D:\MC\.minecraft\libraries\com\mojang\brigadier\1.0.17\brigadier-1.0.17.jar;D:\MC\.minecraft\libraries\com\mojang\datafixerupper\4.0.26\datafixerupper-4.0.26.jar;D:\MC\.minecraft\libraries\com\google\code\gson\gson\2.8.0\gson-2.8.0.jar;D:\MC\.minecraft\libraries\com\mojang\authlib\2.1.28\authlib-2.1.28.jar;D:\MC\.minecraft\libraries\org\apache\commons\commons-compress\1.8.1\commons-compress-1.8.1.jar;D:\MC\.minecraft\libraries\org\apache\httpcomponents\httpclient\4.3.3\httpclient-4.3.3.jar;D:\MC\.minecraft\libraries\commons-logging\commons-logging\1.1.3\commons-logging-1.1.3.jar;D:\MC\.minecraft\libraries\org\apache\httpcomponents\httpcore\4.3.2\httpcore-4.3.2.jar;D:\MC\.minecraft\libraries\it\unimi\dsi\fastutil\8.2.1\fastutil-8.2.1.jar;D:\MC\.minecraft\libraries\org\lwjgl\lwjgl\3.2.2\lwjgl-3.2.2.jar;D:\MC\.minecraft\libraries\org\lwjgl\lwjgl-jemalloc\3.2.2\lwjgl-jemalloc-3.2.2.jar;D:\MC\.minecraft\libraries\org\lwjgl\lwjgl-openal\3.2.2\lwjgl-openal-3.2.2.jar;D:\MC\.minecraft\libraries\org\lwjgl\lwjgl-opengl\3.2.2\lwjgl-opengl-3.2.2.jar;D:\MC\.minecraft\libraries\org\lwjgl\lwjgl-glfw\3.2.2\lwjgl-glfw-3.2.2.jar;D:\MC\.minecraft\libraries\org\lwjgl\lwjgl-stb\3.2.2\lwjgl-stb-3.2.2.jar;D:\MC\.minecraft\libraries\org\lwjgl\lwjgl-tinyfd\3.2.2\lwjgl-tinyfd-3.2.2.jar;D:\MC\.minecraft\libraries\com\mojang\text2speech\1.11.3\text2speech-1.11.3.jar;D:\MC\.minecraft\versions\1.16.5\1.16.5.jar cpw.mods.modlauncher.Launcher --username Tiger__Shark --version "HMCL 3.3.184" --gameDir D:\MC\.minecraft\versions\1.16.5-forge-36.1.16 --assetsDir D:\MC\.minecraft\assets --assetIndex 1.16 --uuid d5e3b40ce17b4dadb33bb264e2b076d4 --accessToken eyJhbGciOiJIUzI1NiJ9.eyJzdWIiOiIyZjM0Y2VmODMyZjBlY2Q4MmMyOTczMDU3NGUyNmViZSIsInlnZ3QiOiI1M2M0NTdkZTVmYmE0NTRhOGUyMWFjZWQzY2MyNzdiNSIsInNwciI6ImQ1ZTNiNDBjZTE3YjRkYWRiMzNiYjI2NGUyYjA3NmQ0IiwiaXNzIjoiWWdnZHJhc2lsLUF1dGgiLCJleHAiOjE2MjEyMjg0NTQsImlhdCI6MTYyMTA1NTY1NH0.KQzr-VN-73lz6zq0Olz703kpKjGO1l-xfgs26_3Enaw --userType mojang --versionType "HMCL 3.3.184" --width 854 --height 480 --launchTarget fmlclient --fml.forgeVersion 36.1.16 --fml.mcVersion 1.16.5 --fml.forgeGroup net.minecraftforge --fml.mcpVersion 20210115.111550
2021-05-15 13:14:26,900 main WARN Advanced terminal features are not available in this environment
[13:14:27] [main/INFO] [cp.mo.mo.Launcher/MODLAUNCHER]: ModLauncher running: args [--username, <player>, --version, HMCL 3.3.184, --gameDir, D:\MC\.minecraft\versions\1.16.5-forge-36.1.16, --assetsDir, D:\MC\.minecraft\assets, --assetIndex, 1.16, --uuid, <uuid>, --accessToken, ????????, --userType, mojang, --versionType, HMCL 3.3.184, --width, 854, --height, 480, --launchTarget, fmlclient, --fml.forgeVersion, 36.1.16, --fml.mcVersion, 1.16.5, --fml.forgeGroup, net.minecraftforge, --fml.mcpVersion, 20210115.111550]
[13:14:27] [main/INFO] [cp.mo.mo.Launcher/MODLAUNCHER]: ModLauncher 8.0.9+86+master.3cf110c starting: java version 16.0.1 by Oracle Corporation
Exception in thread "main" java.lang.IllegalAccessError: class cpw.mods.modlauncher.SecureJarHandler (in unnamed module @0x7ba18f1b) cannot access class sun.security.util.ManifestEntryVerifier (in module java.base) because module java.base does not export sun.security.util to unnamed module @0x7ba18f1b
	at cpw.mods.modlauncher.SecureJarHandler.lambda$static$1(SecureJarHandler.java:41)
	at cpw.mods.modlauncher.api.LamdbaExceptionUtils.uncheck(LamdbaExceptionUtils.java:95)
	at cpw.mods.modlauncher.SecureJarHandler.<clinit>(SecureJarHandler.java:41)
	at cpw.mods.modlauncher.Launcher.lambda$new$6(Launcher.java:55)
	at java.base/java.util.concurrent.ConcurrentHashMap.computeIfAbsent(ConcurrentHashMap.java:1708)
	at cpw.mods.modlauncher.api.TypesafeMap.computeIfAbsent(TypesafeMap.java:52)
	at cpw.mods.modlauncher.api.TypesafeMap.computeIfAbsent(TypesafeMap.java:47)
	at cpw.mods.modlauncher.Environment.computePropertyIfAbsent(Environment.java:62)
	at cpw.mods.modlauncher.Launcher.<init>(Launcher.java:55)
	at cpw.mods.modlauncher.Launcher.main(Launcher.java:66)

 

3 hours ago, diesieben07 said:

Java 16 is not yet supported by Forge.

is there a further plan for java 16?

1 hour ago, diesieben07 said:

Of course, it will have to be supported at least with Minecraft 1.17, as Mojang has switched to using Java 16 with that. It's being worked on.

ok thx

Forge works on J16, you just have to specify the necessary opens arguments to get around the reflection lockdown.

Because those arguments require editing settings in your launcher, and figuring out all the areas Forge and Mods reflect into, it's not something we actively support.