Memory usage of Java

用JDK自带的api计算size，每次都会有个多余的12，看了这些文档终于知道了

1：Memory usage of Java Strings and string-related objects

http://www.javamex.com/tutorials/memory/string_memory_usage.shtml

2：Memory usage of Java objects: general guide

http://www.javamex.com/tutorials/memory/object_memory_usage.shtml

3 How to calculate the memory usage of a Java array

http://www.javamex.com/tutorials/memory/array_memory_usage.shtml

4：Memory usage of Java Strings and string-related objects

http://www.javamex.com/tutorials/memory/string_buffer_memory_usage.shtml