I wanted to try making a mod for minecraft so i was following a tutorial. This one to be exact http://www.minecraftforum.net/forums/mapping-and-modding/mapping-and-modding-tutorials/1571599-1-7-2-modding-with-forge-1-jdk-eclipse-forge-and however minecraft wont launch from eclipse. Can anyone help? This is the message I get:

 

[03:08:56] [main/INFO] [LaunchWrapper]: Loading tweak class name cpw.mods.fml.common.launcher.FMLTweaker

[03:08:56] [main/INFO] [LaunchWrapper]: Using primary tweak class name cpw.mods.fml.common.launcher.FMLTweaker

[03:08:56] [main/INFO] [LaunchWrapper]: Calling tweak class cpw.mods.fml.common.launcher.FMLTweaker

[03:08:56] [main/INFO] [FML]: Forge Mod Loader version 7.2.217.1147 for Minecraft 1.7.2 loading

[03:08:56] [main/INFO] [FML]: Java is Java HotSpot 64-Bit Server VM, version 1.8.0_20, running on Windows 7:amd64:6.1, installed at C:\Program Files\Java\jre1.8.0_20

[03:08:56] [main/INFO] [FML]: Managed to load a deobfuscated Minecraft name- we are in a deobfuscated environment. Skipping runtime deobfuscation

[03:08:56] [main/INFO] [LaunchWrapper]: Loading tweak class name cpw.mods.fml.common.launcher.FMLInjectionAndSortingTweaker

[03:08:56] [main/INFO] [LaunchWrapper]: Loading tweak class name cpw.mods.fml.common.launcher.FMLDeobfTweaker

[03:08:56] [main/INFO] [LaunchWrapper]: Calling tweak class cpw.mods.fml.common.launcher.FMLInjectionAndSortingTweaker

[03:08:56] [main/ERROR] [LaunchWrapper]: Unable to launch

java.util.ConcurrentModificationException

at java.util.ArrayList$Itr.checkForComodification(Unknown Source) ~[?:1.8.0_20]

at java.util.ArrayList$Itr.remove(Unknown Source) ~[?:1.8.0_20]

at net.minecraft.launchwrapper.Launch.launch(Launch.java:117) [launchwrapper-1.9.jar:?]

at net.minecraft.launchwrapper.Launch.main(Launch.java:28) [launchwrapper-1.9.jar:?]

 

I think you are using JRE8 , you need to be using JRE6 or JRE7, I think i read somewhere that jre7 works

 

to change it right click on your project, select "Build Path" >> "Configure Build Path"

select the "libraries" tab, and scroll to the bottom , and check which "JRE System library" you are using

if its "jre8" you need to remove it and add [jre6] or [jre7]

 

you will probably have to search for libraries, on windows search the "program files\java" folder or you wont find any

 

IT WORKED! thank you so much

your welcome,

I had the same problem too