Java String codePoint相关api

codePoint

• 代码点&代码单元，是从Unicode标准而来的术语，Unicode标准的核心是一个编码字符集
• 在java中, 一个字符, 仅仅表明一个代码点(codePoint),
  但却有可能表明多个代码单元(在java中就是两个字节, 一个char),好比表情符😝,
  只表明一个代码点, 却占着两个char

java api

• 首先看一下表情符的length()长度

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

• int codePointAt(int index): 返回char数组的给定索引上的代码点

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

• int codePointBefore(int index): 这里有疑惑, 按理说应该返的代码点值跟上面方法同样才对

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): 返回某个索引区间的代码点数量,
  咱们重点用这个

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

• IntStream codePoints(): 返回全部代码点值的Stream

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

• int offsetByCodePoints(int index, int codePointOffset): 头疼, 后边再分析

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

参考资料

总结的时候发现仍是有些疑问的, 烦烦烦, 待续吧
java的字符编码集
What exactly does String.codePointAt do?