Second part of NPE and arctan update :3

src/main/java/net/minecraft/server/Chunk.java

@@ -6,6 +6,8 @@ import java.util.List;
 import java.util.Map;
 import java.util.Random;
 
+import org.bukkit.craftbukkit.CraftWorld;
+
 public class Chunk {
 
     public static boolean a;
@@ -44,7 +46,8 @@ public class Chunk {
         }
 
         // CraftBukkit start
-        bukkitChunk = ((WorldServer) world).getWorld().popPreservedChunk( i, j );
+        CraftWorld cw = ((WorldServer) world).getWorld();
+        bukkitChunk = (cw == null) ? null:cw.popPreservedChunk( i, j );
         if (bukkitChunk == null) {
             bukkitChunk = new org.bukkit.craftbukkit.CraftChunk( this );
         }

src/main/java/net/minecraft/server/EntityCreature.java

@@ -4,6 +4,7 @@ package net.minecraft.server;
 import org.bukkit.craftbukkit.entity.CraftMonster;
 import org.bukkit.craftbukkit.CraftServer;
 import org.bukkit.craftbukkit.entity.CraftEntity;
+import org.bukkit.craftbukkit.TrigMath;
 import org.bukkit.event.entity.EntityDamageByEntityEvent;
 import org.bukkit.event.entity.EntityDamageEvent;
 import org.bukkit.event.entity.EntityDamageEvent.DamageCause;
@@ -118,7 +119,7 @@ public class EntityCreature extends EntityLiving {
                 double d1 = vec3d.a - this.locX;
                 double d2 = vec3d.c - this.locZ;
                 double d3 = vec3d.b - (double) l1;
-                float f4 = (float) (Math.atan2(d2, d1) * 180.0D / 3.1415927410125732D) - 90.0F;
+                float f4 = (float) (TrigMath.atan2(d2, d1) * 180.0D / 3.1415927410125732D) - 90.0F;
                 float f5 = f4 - this.yaw;
 
                 for (this.by = this.bC; f5 < -180.0F; f5 += 360.0F) {

src/main/java/net/minecraft/server/EntityHuman.java

@@ -4,6 +4,7 @@ import java.util.List;
 
 // CraftBukkit start
 import org.bukkit.craftbukkit.CraftServer;
+import org.bukkit.craftbukkit.TrigMath;
 import org.bukkit.craftbukkit.entity.CraftItemDrop;
 import org.bukkit.entity.Player;
 import org.bukkit.event.entity.EntityDamageByEntityEvent;
@@ -124,7 +125,7 @@ public abstract class EntityHuman extends EntityLiving {
         this.as = this.at;
         super.o();
         float f = MathHelper.a(this.motX * this.motX + this.motZ * this.motZ);
-        float f1 = (float) Math.atan(-this.motY * 0.20000000298023224D) * 15.0F;
+        float f1 = (float) TrigMath.atan(-this.motY * 0.20000000298023224D) * 15.0F;
 
         if (f > 0.1F) {
             f = 0.1F;

src/main/java/net/minecraft/server/EntityLiving.java

@@ -10,6 +10,7 @@ import org.bukkit.craftbukkit.CraftServer;
 import org.bukkit.craftbukkit.CraftWorld;
 import org.bukkit.craftbukkit.entity.CraftEntity;
 import org.bukkit.craftbukkit.inventory.CraftItemStack;
+import org.bukkit.craftbukkit.TrigMath;
 import org.bukkit.event.Event.Type;
 import org.bukkit.event.entity.EntityDamageEvent;
 import org.bukkit.event.entity.EntityDamageEvent.DamageCause;
@@ -236,7 +237,7 @@ public abstract class EntityLiving extends Entity {
         if (f > 0.05F) {
             f3 = 1.0F;
             f2 = f * 3.0F;
-            f1 = (float) Math.atan2(d1, d0) * 180.0F / 3.1415927F - 90.0F;
+            f1 = (float) TrigMath.atan2(d1, d0) * 180.0F / 3.1415927F - 90.0F;
         }
 
         if (this.aY > 0.0F) {

src/main/java/org/bukkit/craftbukkit/CraftChunk.java

@@ -1,6 +1,7 @@
 
 package org.bukkit.craftbukkit;
 
+import java.lang.ref.WeakReference;
 import java.util.HashMap;
 
 import net.minecraft.server.WorldServer;
@@ -11,27 +12,38 @@ import org.bukkit.block.Block;
 import org.bukkit.craftbukkit.block.CraftBlock;
 
 public class CraftChunk implements Chunk {
-    private net.minecraft.server.Chunk chunk;
+    private WeakReference<net.minecraft.server.Chunk> weakChunk;
     private final HashMap<Integer, Block> cache = new HashMap<Integer, Block>();
-
+    private WorldServer worldServer;
+    private int x;
+    private int z;
+    
     public CraftChunk(net.minecraft.server.Chunk chunk) {
-        this.chunk = chunk;
+        this.weakChunk = new WeakReference<net.minecraft.server.Chunk>(chunk);
+        worldServer = (WorldServer) getHandle().d;
+        x = getHandle().j;
+        z = getHandle().k;
     }
 
     public World getWorld() {
-        return ((WorldServer) chunk.d).getWorld();
+        return worldServer.getWorld();
     }
 
     public net.minecraft.server.Chunk getHandle() {
-        return chunk;
+        net.minecraft.server.Chunk c = weakChunk.get();
+        if (c == null) {
+            weakChunk = new WeakReference<net.minecraft.server.Chunk>(worldServer.c(x,z));
+            c = weakChunk.get();
+        }
+        return c;
     }
 
     public int getX() {
-        return chunk.j;
+        return x;
     }
 
     public int getZ() {
-        return chunk.k;
+        return z;
     }
 
     @Override
@@ -48,8 +60,5 @@ public class CraftChunk implements Chunk {
         }
         return block;
     }
-
-    public void breakLink() {
-        this.chunk = null;
-    }
 }
+

src/main/java/org/bukkit/craftbukkit/CraftWorld.java

@@ -47,12 +47,11 @@ public class CraftWorld implements World {
     }
 
     public void preserveChunk( CraftChunk chunk ) {
-        chunk.breakLink();
-        unloadedChunks.put( chunk.getX() << 16 + chunk.getZ(), chunk );
+        unloadedChunks.put( (chunk.getX() << 16) + chunk.getZ(), chunk );
     }
 
     public CraftChunk popPreservedChunk( int x, int z ) {
-        return unloadedChunks.remove( x << 16 + z );
+        return unloadedChunks.remove( (x << 16) + z );
     }
 
     public Block getBlockAt(int x, int y, int z) {

src/main/java/org/bukkit/craftbukkit/TrigMath.java

@@ -1,6 +1,7 @@
 package org.bukkit.craftbukkit;
 /**
- * Got this code from a post by user aioobe on stackoverflow.com
+ * Credits for this class goes to user aioobe on stackoverflow.com
+ * Source: http://stackoverflow.com/questions/4454630/j2me-calculate-the-the-distance-between-2-latitude-and-longitude
  *
  */
 public class TrigMath {