Java StringBuilder codePointAt()示例

StringBuilder类的 codePointAt(int index) 方法以一个索引为参数，返回StringBuilder所包含的字符串中该索引处的一个字符的unicode点，或者我们可以说charPointAt()方法返回该索引处字符的 “unicode号码”。索引指的是char值（Unicode代码单位），索引的值必须在0到length-1之间。

如果出现在给定索引上的char值位于高代用范围内，下面的索引小于这个序列的长度，并且下面索引上的char值位于低代用范围内，那么将返回与这个代用对对应的补充码位。否则，将返回给定索引处的char值。

语法

public int codePointAt(int index)

参数： 该方法接受一个int类型的参数 index ，代表要返回unicode值的字符的索引。

返回值： 该方法返回指定位置上的字符的 “unicode号码”。

异常： 当index为负数或大于等于length()时，该方法会产生 IndexOutOfBoundsException 。

以下程序演示了StringBuilder类的codePointAt()方法。

例1:

// Java program to demonstrate// the codePointAt() method  class GFG {    public static void main(String[] args)    {          // create a StringBuilder object        StringBuilder str = new StringBuilder();          // add the String to StringBuilder Object        str.append("Geek");          // get unicode of char at position 1        int unicode = str.codePointAt(1);          // print the result        System.out.println("StringBuilder Object"                           + " contains = " + str);        System.out.println("Unicode of Character"                           + " at Position 1 "                           + "in StringBuilder = "                           + unicode);          // get unicode of char at position 3        unicode = str.codePointAt(3);          // print the result        System.out.println("Unicode of Character "                           + "at Position 3 "                           + "in StringBuilder = "                           + unicode);    }}

输出:

StringBuilder Object contains = GeekUnicode of Character at Position 1 in StringBuilder = 101Unicode of Character at Position 3 in StringBuilder = 107

例2:

// Java program to demonstrate// the codePointAt() Method.  class GFG {    public static void main(String[] args)    {          // create a StringBuilder object        // with a String pass as parameter        StringBuilder            str            = new StringBuilder("WelcomeGeeks");          // print string        System.out.println("String is " + str.toString());          // loop through string and print every Character        for (int i = 0; i < str.length(); i++) {              // get char at position i            char ch = str.charAt(i);              // get unicode of char at position i            int unicode = str.codePointAt(i);              // print char and Unicode            System.out.println("Unicode of Char " + ch                               + " at position " + i                               + " is " + unicode);        }    }}

输出:

String is WelcomeGeeksUnicode of Char W at position 0 is 87Unicode of Char e at position 1 is 101Unicode of Char l at position 2 is 108Unicode of Char c at position 3 is 99Unicode of Char o at position 4 is 111Unicode of Char m at position 5 is 109Unicode of Char e at position 6 is 101Unicode of Char G at position 7 is 71Unicode of Char e at position 8 is 101Unicode of Char e at position 9 is 101Unicode of Char k at position 10 is 107Unicode of Char s at position 11 is 115

例3：演示IndexOutOfBoundsException

// Java program demonstrate// IndexOutOfBoundsException thrown by// the codePointAt() Method.  class GFG {    public static void main(String[] args)    {        // create a StringBuilder object        // with a String pass as parameter        StringBuilder            str            = new StringBuilder("WelcomeGeeks");          try {              // get char at position out of range of index            int i = str.codePointAt(str.length());        }          catch (IndexOutOfBoundsException e) {            System.out.println("Exception: " + e);        }    }}

输出:

Exception: java.lang.StringIndexOutOfBoundsException: String index out of range: 12

参考资料：
https://docs.oracle.com/javase/10/docs/api/java/lang/StringBuilder.html#codePointAt(int)