A friend of mine asked me why his Java batch job reading a 23MB text file took over 300MB Memory. He read some text and date values and stored them in String an Calendar objects. A short web search brought up this blog post of Jason Rennie writing about the size of java.util.Calendar. He points out that a single instance of java.util.Calendar takes 432 bytes of memory. This was the explanation – 500000 calendar objects need 206MB memory! This was new to me …