If asked the question, "What is the difference between UTF-8 and Unicode?", would you confidently reply with a short and precise answer? In these days of internationalization all developers should be able to do that. I suspect many of us do not understand these concepts as well as we should. If you feel you belong to this group, you should read this ultra short introduction to character sets and encodings.
Actually, comparing UTF-8 and Unicode is like comparing apples and oranges:
UTF-8 is an encoding - Unicode is a character set
A character set is a list of characters with unique numbers (these numbers are sometimes referred to as "code points"). For example, in the Unicode character set, the number for A is 41.
An encoding on the other hand, is an algorithm that translates a list of numbers to binary so it can be stored on disk. For example UTF-8 would translate the number sequence 1, 2, 3, 4 like this:
00000001 00000010 00000011 00000100 Our data is now translated into binary and can now be saved to disk.
All together now
Say an application reads the following from the disk:
1101000 1100101 1101100 1101100 1101111 The app knows this data represent a Unicode string encoded with UTF-8 and must show this as text to the user. First step, is to convert the binary data to numbers. The app uses the UTF-8 algorithm to decode the data. In this case, the decoder returns this:
104 101 108 108 111 Since the app knows this is a Unicode string, it can assume each number represents a character. We use the Unicode character set to translate each number to a corresponding character. The resulting string is "hello".
Conclusion
So when somebody asks you "What is the difference between UTF-8 and Unicode?", you can now confidently answer short and precise:
UTF-8 and Unicode cannot be compared. UTF-8 is an encoding used to translate numbers into binary data. Unicode is a character set used to translate characters into numbers.
文章轉自：http://stackoverflow.com/questions/3951722/whats-the-difference-between-unicode-and-utf8
Java中採用的是unicode標準字符集
Java語言使用unicode標準字符集，最多可以識別65535個字符，unicode字符表的前128個字符剛好是ASCII表。每個國家的“字母表”的字母都是unicode表中的一個字符，比如漢字中的“你”字就是unicode表中的第20320字符。
Java所謂的字母包括了世界上任何語言中的“字母表”，因此，Java所使用的字母不僅包括通常的拉丁字母，a,b,c等，也包括漢語中的漢字，日文裏的片假名，平假名，朝鮮文以及其他許多語言中的文字。
維基百科：
目前實際應用的統一碼版本是UCS-2，使用16位的編碼空間。也就是每個字符(character，即char)佔用2個字節(byte)。這樣理論上一共最多可以表示2^16（即65536）個字符。基本滿足各種語言的使用。實際上當前版本的統一碼並未完全使用這16位編碼，而是保留了大量空間以作爲特殊使用或將來擴展。
Java的字節碼環境採用UTF-16作爲內部表示，UTF-16繼承自UCS-2，使用16位的編碼空間。所以Java中基本類型char的大小是16-bit，範圍是：Unicode 0 ~ Unicode 2^16-1。
