字符串indexOf(int ch)方法 (String indexOf(int ch) Method)

indexOf(int ch) is a String method in Java and it is used to get the index of a specified character in the string.

indexOf(int ch)是Java中的String方法，用于获取字符串中指定字符的索引。

If the character exists in the string, it returns the index of the first occurrence of the character, if the character does not exist in the string, it returns -1.

如果该字符存在于字符串中，则返回该字符首次出现的索引，如果该字符不存在于字符串中，则返回-1。

Syntax:

句法：

    int str_object.indexOf(int chr);

Here,

这里，

• str_object is an object of main string in which we have to find the index of given character.

  str_object是主字符串的对象，我们必须在其中找到给定字符的索引。

• chr is a character to be found in the string.

  chr是在字符串中找到的字符。

It accepts a character and returns an index of its first occurrence or -1 if the character does not exist in the string.

它接受一个字符并返回其首次出现的索引；如果字符串中不存在该字符，则返回-1。

Example:

例：

    Input: 
String str = "IncludeHelp"
Function call:
str.indexOf('H')
Output:
7
Input: 
String str = "IncludeHelp"
Function call:
str.indexOf('W')
Output:
-1

Java code to demonstrate the example of String.indexOf() method

Java代码演示String.indexOf()方法的示例

public class Main
{
public static void main(String[] args) {
String str = "IncludeHelp";
char ch;
int index;
ch = 'H';
index = str.indexOf(ch);
if(index != -1)
System.out.println(ch + " is found at " + index + " position.");
else 
System.out.println(ch + " does not found.");
ch = 'e';
index = str.indexOf(ch);
if(index != -1)
System.out.println(ch + " is found at " + index + " position.");
else 
System.out.println(ch + " does not found.");            
ch = 'W';
index = str.indexOf(ch);
if(index != -1)
System.out.println(ch + " is found at " + index + " position.");
else 
System.out.println(ch + " does not found.");            
}
}

Output

输出量

H is found at 7 position.
e is found at 6 position.
W does not found.

翻译自: https://www.includehelp.com/java/string-indexOf-int-ch-method-with-example.aspx