Java开发网 - java /unicode /UTF-8

Topic: java /unicode /UTF-8

1.java /unicode /UTF-8

Posted by: zerol
Posted on: 2003-12-27 17:13

请问为什么说 in memory every char is at least 2 bytes，怎么理解 at least?

excerpted from Sizeof for Java --Object sizing revisited by JW
http://www.javaworld.com/javaworld/javaqa/2003-12/02-qa-1226-sizeof.html?

Fallacy: You can measure an object's size by serializing it into a byte stream and looking at the resulting stream length
The reason this does not work is because the serialization layout is only a remote reflection of the true in-memory layout. One easy way to see it is by looking at how Strings get serialized: in memory every char is at least 2 bytes, but in serialized form Strings are UTF-8 encoded and so any ASCII content takes half as much space.

2.Re:java /unicode /UTF-8 [Re: zerol]

Copy to clipboard

Posted by: dingligang
Posted on: 2003-12-29 16:53

unicode是一种编码方式，和ascii是同一个概念，而UTF-8是一种存储方式（格式）。

在jvm内部，虚拟机管理数据（内存里）时，或者在进行对象序列化的时候，字符（串）都是以unicode编码方式的。
但是在jvm中，字符（串）是以char这种（存储）形式存放的，一个char占2个字节（例如可以定义char c='字'），就是“字”和“Z”是同样占2个字节的；
而在对象序列化后，对象是进行UTF-8存储的，一个中文占2个字节，而英文、数字等只占一个字节，可以参看下面的链接。

所以导致系列化以后的对象只占平时的大约一半的空间（当全是中文时占用相同的空间；全是英文时unicode占用的空间是UTF-8的2倍）。

关于Unicode：
http://www.3552808.com/gy/dl/ShowArticle.asp?ArticleID=155

关于UTF-8：
http://www.ctosoft.com/book/utf8.html