Java StringBuilder codePointBefore()用法及代码示例

StringBuilder类的codePointBefore()方法将索引作为参数，并返回StringBuilder包含的String中指定索引之前的字符的“Unicode number”。索引引用char值(Unicode代码单位)，并且索引的值必须介于0到length-1之间。

如果(index-1)处的char值在低代理范围内，(index-2)处的char不为负且值在高代理范围内，则返回代理对的补充代码点值通过方法。如果索引-1处的char值是未配对的低代理或高代理，则返回代理值。

用法:

public int codePointBefore(int index)

参数：此方法接受一个int型参数索引，该索引表示要返回其unicode值的字符之后的字符的索引。

返回值：此方法返回给定索引之前的字符的“unicode number”。

异常：当index为负或大于或等于length()时，此方法将引发IndexOutOfBoundsException。

下面的程序演示StringBuilder类的codePointBefore()方法：

范例1：

// Java program to demonstrate 
// the codePointBefore() 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()); 
  
        // get unicode of char at index 1 
        // using codePointBefore() method 
        int unicode = str.codePointBefore(2); 
  
        // print char and Unicode 
        System.out.println("Unicode of character"
                           + " at position 1 = " + unicode); 
  
        // get unicode of char at index 10 
        // using codePointBefore() method 
        unicode = str.codePointBefore(11); 
  
        // print char and Unicode 
        System.out.println("Unicode of character"
                           + " at position 10 = "
                           + unicode); 
    } 
}

输出：

String is WelcomeGeeks
Unicode of character at position 1 = 101
Unicode of character at position 10 = 107

范例2：演示IndexOutOfBoundsException

// Java program to demonstrate 
// exception thrown by codePointBefore() 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 unicode of char at position 1ength + 2 
            int unicode = str.codePointBefore( 
                str.length() + 2); 
        } 
  
        catch (Exception e) { 
            System.out.println("Exception:" + e); 
        } 
    } 
}

输出：

Exception:java.lang.StringIndexOutOfBoundsException:
 String index out of range:14

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

相关用法

注：本文由纯净天空筛选整理自AmanSingh2210大神的英文原创作品 StringBuilder codePointBefore() in Java with Examples。非经特殊声明，原始代码版权归原作者所有，本译文未经允许或授权，请勿转载或复制。