Java String codePoint相關api

codePoint

• 代碼點&代碼單元，是從Unicode標准而來的術語，Unicode標准的核心是一個編碼字符集
• 在java中, 一個字符, 僅僅代表一個代碼點(codePoint),
  但卻有可能代表多個代碼單元(在java中就是兩個字節, 一個char),比如表情符😝,
  只代表一個代碼點, 卻占着兩個char

java api

• 首先看一下表情符的length()長度

int length = "😁".length();
System.out.println("length " + length);//2

• int codePointAt(int index): 返回char數組的給定索引上的代碼點

int at1 = "😁".codePointAt(0);
System.out.println("at1 " + at1);//128513
int at2 = "😁".codePointAt(1);
System.out.println("at2 " + at2);//56833

• int codePointBefore(int index): 這里有疑惑, 按理說應該返的代碼點值跟上面方法一樣才對

int before1 = "😁".codePointBefore(1);
System.out.println("before1 " + before1);//55357
int before2 = "😁".codePointBefore(2);
System.out.println("before2 " + before2);//128513

• int codePointCount(int beginIndex, int endIndex): 返回某個索引區間的代碼點數量,
  我們重點用這個

int count = "😁".codePointCount(0, "😁".length()-1);
System.out.println("count " + count);//1

• IntStream codePoints(): 返回所有代碼點值的Stream

"😁".codePoints().boxed().forEach(
        integer -> System.out.println(integer));

• int offsetByCodePoints(int index, int codePointOffset): 頭疼, 后邊再分析

int offset = "😁😁".offsetByCodePoints(1, 2);
System.out.println("offset " + offset);//4

參考資料

總結的時候發現還是有些疑問的, 煩煩煩, 待續吧
java的字符編碼集
What exactly does String.codePointAt do?