Versuch es mal so
Code
Process exec = Runtime.getRuntime().exec("java -Xms256M -Xmx1024M -Djava.library.path="+minecraftdir+"bin\natives -cp "+minecraftdir+"bin\minecraft.jar; "+minecraftdir+"bin\jinput.jar;"+minecraftdir+"bin\lwjgl.jar;"+minecraftdir+"bin\lwjgl_util.jar net.minecraft.client.Minecraft "+login +" "+session);
/- Zeilen Umbruch