What is the lib\modules file in JDK 11 installation directory?

lib\modules file in JDK 11 installation directory is the runtime JImage file of all Java language modules and all JDK tool modules.

You can list all modules and classes in lib\modules using the "jimage list" command:

C:>dir \fyicenter\jdk-11.0.1\bin\jimage list \fyicenter\jdk-11.0.1\lib\modules

jimage: \fyicenter\jdk-11.0.1\lib\modules

Module: java.base
    META-INF/services/java.nio.file.spi.FileSystemProvider
    com/sun/crypto/provider/AESCipher$AES128_CBC_NoPadding.class
    com/sun/crypto/provider/AESCipher$AES128_CFB_NoPadding.class
    com/sun/crypto/provider/AESCipher$General.class
    com/sun/crypto/provider/AESCipher$OidImpl.class
    com/sun/crypto/provider/AESCipher.class
    com/sun/crypto/provider/AESConstants.class
    com/sun/crypto/provider/AESCrypt.class
    com/sun/crypto/provider/AESKeyGenerator.class
    com/sun/crypto/provider/AESParameters.class
    com/sun/crypto/provider/AESWrapCipher$AES128.class
    com/sun/crypto/provider/AESWrapCipher$AES192.class
    com/sun/crypto/provider/AESWrapCipher$AES256.class
    com/sun/crypto/provider/AESWrapCipher$General.class
    com/sun/crypto/provider/AESWrapCipher.class
    com/sun/crypto/provider/ARCFOURCipher.class
    com/sun/crypto/provider/BlockCipherParamsCore.class
    com/sun/crypto/provider/BlowfishCipher.class
    com/sun/crypto/provider/BlowfishConstants.class
    com/sun/crypto/provider/BlowfishCrypt.class
    com/sun/crypto/provider/BlowfishKeyGenerator.class
    ...
Module: java.compiler
    javax/annotation/processing/AbstractProcessor.class
    javax/annotation/processing/Completion.class
    javax/annotation/processing/Completions$SimpleCompletion.class
    javax/annotation/processing/Completions.class
    javax/annotation/processing/Filer.class
    ...

⇒ JDK 11 lib/src.zip - Source Code

⇐ JDK 11 jmods/*.jmod - List of JMod Files

⇑ Download and Use JDK 11

⇑⇑ FAQ for JDK (Java Development Kit)