How much memory is allocated to the String object in Java

	Size in bytes
String() object
Object header	16
Hash field	4
Reference to char array	4
Char[] array
Object header	16
Array length	4
Array size	N*2

String allocates in memory at least (24+20+N*2) bytes, where N - number of characters in the string. If N=10 then string size = 64 bytes.

One million of these strings = 64 000 000 bytes. But also we need array or collection to store these strings.
This requires additional memory.
ArrayList<String>(1 000 000) ~= 4 000 000 bytes (4 bytes per reference to string object).

So, total size will be 68 000 000 bytes.

Gist code: Output:

3,355,792 Initial
1,217,624 After GC
218,921,768 Created list of strings
76,489,936 After GC
68,000,000 Expected size in memory

But if you have many similar strings, then using of String.intern() greatly reduces amount of allocated memory. Output:

3,355,792 Initial
1,217,792 After GC
106,750,232 Created list of strings
13,127,480 After GC
68,000,000 Expected size in memory

10x less memory! 6.8 megabytes instead of 68

The best resolutions

List of multiple resolutions in the most popular proportions:

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Read SAS file in Java

Some companies (banks, medical and pharmaceutical companies) store their data in the SAS (.sas7bdat) format. This is old, legacy, but still actual format for tabular data. And this format is proprietary and fiddly.

But what if you have to work with the data from the sas-file? For me, solution is pretty simple - convert the data from the sas-file to some convenient and popular format. For example, to the MongoDB. And then access this data via nice query-like API.

In my new mini-project sas2mongo I show how to convert data from the sas-file into the MongoDB in Java.

Sas2Mongo

I've just released my new micro-project: sas2mongo

This is a command line tool for copying data from sas-files to mongo-db.

Me on GitHub

I'm moving my projects to GitHub.

Most of them are open and free for all.

Me on GitHub
My GitHub pages

Already moved projects:

• MusicBox (sources and demo) - digital musicbox
• Harmonica (sources and demo) - set of musical instruments
• Xameleon (demo) - webcam application
• XenoHarmonica (demo) - MIDI bayan (russian accordion) emulator
• Pkmx (sources and demo) - JavaScript library for optimal blocks layout
• WebTools (sources and demo) - collection of online web tools