Java 中的 StringBuilder codePointBefore()示例
原文:https://www . geeksforgeeks . org/stringbuilder-code points-in-Java-with-examples/
StringBuilder 类的 codePointBefore() 方法以索引为参数，返回 StringBuilder 包含的字符串中指定索引前的字符的“Unicode 编号”。索引引用字符值(Unicode 代码单位)，索引的值必须介于 0 到长度-1 之间。
如果(index–1)处的 char 值在低代理范围内，而(index–2)处的 char 值在高代理范围内，则方法返回代理对的补充代码点值。如果索引–1 处的字符值是不成对的低代理项或高代理项，则返回代理项值。
语法:
public int codePointBefore(int index)
参数:该方法接受一个 int 类型参数索引表示要返回 unicode 值的字符后面的字符的索引。
返回值:该方法返回给定索引前字符的“unicode 数字”。
异常:当索引为负或大于等于长度()时，此方法抛出indexout of boundsexception。
下面的程序演示了 StringBuilder 类的 codePointBefore()方法:
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);
}
}
Output:
String is WelcomeGeeks
Unicode of character at position 1 = 101
Unicode of character at position 10 = 107
示例 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);
}
}
}
Output:
Exception: java.lang.StringIndexOutOfBoundsException:
String index out of range: 14
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