i create a new world and my game crashes:
---- Minecraft Crash Report ----
// I just don't know what went wrong

Time: 29/11/12 01:49 PM
Description: Exception in server tick loop

java.lang.OutOfMemoryError: Java heap space
at java.util.TreeMap.put(Unknown Source)
at java.util.TreeSet.add(Unknown Source)
at in.a(SourceFile:335)
at in.a(SourceFile:307)
at akg.g(SourceFile:24)
at zs.a(SourceFile:401)
at zs.a(SourceFile:338)
at xv.b(SourceFile:315)
at abv.a(SourceFile:31)
at yv.a(SourceFile:73)
at yv.a(SourceFile:27)
at yr.a(SourceFile:217)
at zd.a(SourceFile:48)
at aau.a(SourceFile:450)
at im.a(SourceFile:165)
at zs.a(SourceFile:719)
at im.c(SourceFile:104)
at net.minecraft.server.MinecraftServer.e(SourceFile:513)
at bdo.a(SourceFile:83)
at bdo.c(SourceFile:99)
at net.minecraft.server.MinecraftServer.run(SourceFile:595)
at fy.run(SourceFile:856)

A detailed walkthrough of the error, its code path and all known details is as follows:
---------------------------------------------------------------------------------------

– System Details –
Details:
Minecraft Version: 1.4.5
Operating System: Windows 7 (x86) version 6.1
Java Version: 1.7.0_09, Oracle Corporation
Java VM Version: Java HotSpot(TM) Client VM (mixed mode, sharing), Oracle Corporation
Memory: 8914464 bytes (8 MB) / 259522560 bytes (247 MB) up to 259522560 bytes (247 MB)
JVM Flags: 0 total;
AABB Pool Size: 0 (0 bytes; 0 MB) allocated, 0 (0 bytes; 0 MB) used
Suspicious classes: IWrUpdater, Config, WrUpdaterSmooth, ...]
IntCache: cache: 2, tcache: 0, allocated: 1, tallocated: 63
Profiler Position: N/A (disabled)
Vec3 Pool Size: 0 (0 bytes; 0 MB) allocated, 0 (0 bytes; 0 MB) used
Player Count: 0 / 8; []
Type: Integrated Server (map_client.txt)
Is Modded: Very likely; Jar signature invalidated
And i dont use any mod