日志：
[21:17:39] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:-1]: java.lang.NoClassDefFoundError: net/minecraftforge/fml/relauncher/IFMLLoadingPlugin
[21:17:39] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:-1]: at java.lang.ClassLoader.defineClass1(Native Method)
[21:17:39] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:-1]: at java.lang.ClassLoader.defineClass(Unknown Source)
[21:17:39] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:-1]: at java.security.SecureClassLoader.defineClass(Unknown Source)
[21:17:39] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:-1]: at java.net.URLClassLoader.defineClass(Unknown Source)
[21:17:39] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:-1]: at java.net.URLClassLoader.access$100(Unknown Source)
[21:17:39] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:-1]: at java.net.URLClassLoader$1.run(Unknown Source)
[21:17:39] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:-1]: at java.net.URLClassLoader$1.run(Unknown Source)
[21:17:39] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:-1]: at java.security.AccessController.doPrivileged(Native Method)
[21:17:39] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:-1]: at java.net.URLClassLoader.findClass(Unknown Source)
[21:17:39] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:-1]: at net.minecraft.launchwrapper.LaunchClassLoader.findClass(LaunchClassLoader.java:117)
[21:17:39] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:-1]: at java.lang.ClassLoader.loadClass(Unknown Source)
[21:17:39] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:-1]: at java.lang.ClassLoader.loadClass(Unknown Source)
[21:17:39] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:-1]: at java.lang.Class.forName0(Native Method)
[21:17:39] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:-1]: at java.lang.Class.forName(Unknown Source)
[21:17:39] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:-1]: at cpw.mods.fml.relauncher.CoreModManager.loadCoreMod(CoreModManager.java:460)
[21:17:39] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:-1]: at cpw.mods.fml.relauncher.CoreModManager.discoverCoreMods(CoreModManager.java:389)
[21:17:39] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:-1]: at cpw.mods.fml.relauncher.CoreModManager.handleLaunch(CoreModManager.java:221)
[21:17:39] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:-1]: at cpw.mods.fml.relauncher.FMLLaunchHandler.setupHome(FMLLaunchHandler.java:90)
[21:17:39] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:-1]: at cpw.mods.fml.relauncher.FMLLaunchHandler.setupClient(FMLLaunchHandler.java:67)
[21:17:39] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:-1]: at cpw.mods.fml.relauncher.FMLLaunchHandler.configureForClientLaunch(FMLLaunchHandler.java:34)
[21:17:39] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:-1]: at cpw.mods.fml.common.launcher.FMLTweaker.injectIntoClassLoader(FMLTweaker.java:126)
[21:17:39] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:-1]: at net.minecraft.launchwrapper.Launch.launch(Launch.java:115)
[21:17:39] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:-1]: at net.minecraft.launchwrapper.Launch.main(Launch.java:28)
[21:17:39] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:-1]: Caused by: java.lang.ClassNotFoundException: net.minecraftforge.fml.relauncher.IFMLLoadingPlugin
[21:17:39] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:-1]: at net.minecraft.launchwrapper.LaunchClassLoader.findClass(LaunchClassLoader.java:191)
[21:17:39] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:-1]: at java.lang.ClassLoader.loadClass(Unknown Source)
[21:17:39] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:-1]: at java.lang.ClassLoader.loadClass(Unknown Source)
[21:17:39] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:-1]: ... 23 more
[21:17:39] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:-1]: Caused by: java.lang.NullPointerException
[21:17:39] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:-1]: at net.minecraft.launchwrapper.LaunchClassLoader.findClass(LaunchClassLoader.java:182)
[21:17:39] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:-1]: ... 25 more
Exception in thread "main"
你是不是向里面加 mod 了，而且似乎还是版本不对应的 mod