Minecraft Forge 1.7.10 will not start [closed]

Question

My minecraft will not start on only that version, I have a Windows 7 computer with Java 8u20 installed, because the latest java 7 update will not work at all(plus imma dev for other stuff).

 [22:26:39] [main/INFO] [LaunchWrapper]: Loading tweak class name 
 cpw.mods.fml.common.launcher.FMLTweaker
 [22:26:39] [main/INFO] [LaunchWrapper]: Using primary tweak class name 
 cpw.mods.fml.common.launcher.FMLTweaker
 [22:26:39] [main/INFO] [LaunchWrapper]: Calling tweak class 
 cpw.mods.fml.common.launcher.FMLTweaker
 [22:26:40] [main/INFO] [FML]: Forge Mod Loader version 7.10.25.1208 for Minecraft 
 1.7.10 loading
 [22:26:40] [main/INFO] [FML]: Java is Java HotSpot(TM) 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
 [22:26:40] [main/INFO] [LaunchWrapper]: Loading tweak class name 
 cpw.mods.fml.common.launcher.FMLInjectionAndSortingTweaker
 [22:26:40] [main/INFO] [LaunchWrapper]: Loading tweak class name 
 cpw.mods.fml.common.launcher.FMLDeobfTweaker
 [22:26:40] [main/INFO] [LaunchWrapper]: Calling tweak class 
 cpw.mods.fml.common.launcher.FMLInjectionAndSortingTweaker
 [22:26:40] [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:?]
 Java HotSpot(TM) 64-Bit Server VM warning: Using incremental CMS is deprecated and 
 will likely be removed in a future release

Answer 1

Forge does not support Java 1.8 at the moment. You can fix this error by downgrading java to 1.7

Alternatively you can also have 2 java installation and point forge to launch with 1.7 instead of 1.8. All you need to do is modify the java path in the minecraft launcher:

Select the profile in the launcher, and press "Edit Profile", then under "Java Settings (Advanced)" change the path to the location of jre7. Save your profile, and play:

Answer 2

DarkDestry is right but it only works for 1.7.2 on my computer.

Download Java 7 again: http://java.com/en/download/manual_java7.jsp

Then edit the profile and tick the advanced java option and change the line with this: C:\Program Files (x86)\Java\jre7\bin\javaw.exe

Execute!

*If Java 7 URL Doesn't work use this one (Maybe since April 2015):
http://www.oracle.com/technetwork/java/javase/archive-139210.html