Java StringBuffer codePointCount()方法及实例

StringBuffer类的 codePointCount() 方法用于返回StringBuffer包含的String的beginIndex到endIndex的指定范围内的Unicode代码点的数量。该方法将beginIndex和endIndex作为参数，其中beginIndex是文本范围内第一个字符的索引，endIndex是文本范围内最后一个字符后的索引。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。范围从beginIndex开始，在索引endIndex-1的字符处结束。因此，文本范围的长度（以字符为单位）是endIndex-beginIndex。

语法

public int codePointCount(int beginIndex,
                               int endIndex)

参数： 该方法需要两个参数。

• beginIndex : int值，代表文本范围的第一个字符的索引。
• endIndex ：代表文本范围内最后一个字符的索引的int值。

返回值 ：该方法返回int值，代表指定文本范围内的Unicode代码点的数量。

异常： 如果出现以下情况，该方法会抛出IndexOutOfBoundsException。

• the beginIndex小于0。
• 或者endIndex大于String的长度。
• 或者beginIndex大于endIndex。

下面的程序说明了StringBuffer.codePointCount()方法。

例1 :

// Java program to demonstrate
// the codePointCount() Method.
  
class GFG {
    public static void main(String[] args)
    {
  
        // create a StringBuffer object
        // with a String pass as parameter
        StringBuffer
            str
            = new StringBuffer("Welcome to GeeksforGeeks");
  
        // print string
        System.out.println("String = " + str.toString());
  
        // returns the codepoint count from index 4 to 10
        int codepoints = str.codePointCount(4, 10);
  
        System.out.println("No of Unicode code points "
                           + " between index 4 and index 10 = "
                           + +codepoints);
    }
}

输出:

String = Welcome to GeeksforGeeks
No of Unicode code points  between index 4 and index 10 = 6

例2 :

// Java program to demonstrate
// the codePointCount() Method.
  
class GFG {
    public static void main(String[] args)
    {
  
        // create a StringBuffer object
        // with a String pass as parameter
        StringBuffer
            str
            = new StringBuffer("GeeksForGeeks contribute");
  
        // print string
        System.out.println("String = "
                           + str.toString());
  
        // returns the codepoint count
        // from index 3 to 7
        int
            codepoints
            = str.codePointCount(13, 17);
  
        System.out.println("No of Unicode code points"
                           + " between index 13 and 17 = "
                           + codepoints);
    }
}

输出:

String = GeeksForGeeks contribute
No of Unicode code points between index 13 and 17 = 4

例3： 演示IndexOutOfBoundsException

// Java program to demonstrate
// exception thrown by the codePointCount() Method.
  
class GFG {
    public static void main(String[] args)
    {
  
        // create a StringBuffer object
        // with a String pass as parameter
        StringBuffer
            str
            = new StringBuffer("GeeksForGeeks");
  
        try {
  
            // make beginIndex greater than endIndex
            int codepoints = str.codePointCount(2, 0);
        }
  
        catch (Exception e) {
            System.out.println("Exception: " + e);
        }
    }
}

输出:

Exception: java.lang.IndexOutOfBoundsException

参考文献：
https://docs.oracle.com/javase/10/docs/api/java/lang/StringBuffer.html#codePointCount(int, int)