RegionFileCache.java

    private RegionFile a(ChunkCoordIntPair chunkcoordintpair) throws IOException {
        long i = ChunkCoordIntPair.pair(chunkcoordintpair.getRegionX(), chunkcoordintpair.getRegionZ());
        RegionFile regionfile = (RegionFile) this.cache.getAndMoveToFirst(i);

        if (regionfile != null) {
            return regionfile;
        } else {
            if (this.cache.size() >= 256) {
                this.cache.removeLast(); // The relevant line. 
            }

            if (!this.a.exists()) {
                this.a.mkdirs();
            }

            File file = new File(this.a, "r." + chunkcoordintpair.getRegionX() + "." + chunkcoordintpair.getRegionZ() + ".mca");
            RegionFile regionfile1 = new RegionFile(file);

            this.cache.putAndMoveToFirst(i, regionfile1);
            return regionfile1;
        }
    }