Use the indexOf() method of the StringBuilder class in Java to find specified characters or substrings in a string

In Java, use the indexOf() method of the StringBuilder class to find a specified character or substring in a string.

In Java programming, sometimes we need to find a specified character or subcharacter in a string. string and get its position in the string. Java provides the indexOf() method of the StringBuilder class to implement this function.

StringBuilder is a mutable string that allows us to perform string operations, including inserting and deleting characters, without creating a new string object. The indexOf() method is one of the methods provided by the StringBuilder class. It can find a specified character or substring in a string and return the position of its first occurrence in the string.

The following is a sample code that uses the indexOf() method of the StringBuilder class to find characters:

public class IndexOfExample {
    public static void main(String[] args) {
        StringBuilder sb = new StringBuilder("Hello, World!");
        char ch = 'o';
        int index = sb.indexOf(String.valueOf(ch));
        System.out.println("字符 '" + ch + "' 第一次出现的位置：" + index);
    }
}

In the above code, we first create a StringBuilder object sb and initialize it as "Hello, World!". Then we define a character ch equal to 'o' and use the indexOf() method to find the first occurrence of the character 'o' in the string. Finally, we print the results.

The output result is:

字符 'o' 第一次出现的位置：4

The indexOf() method parameter in the above example can be a character or a string. If what we need to find is a substring, we can convert it to a string and then search it through the indexOf() method. The following is a sample code that uses the indexOf() method of the StringBuilder class to find a substring:

public class IndexOfExample {
    public static void main(String[] args) {
        StringBuilder sb = new StringBuilder("Hello, World!");
        String str = "Wo";
        int index = sb.indexOf(str);
        System.out.println("子字符串 '" + str + "' 第一次出现的位置：" + index);
    }
}

In the above code, we initialize the StringBuilder object sb to "Hello, World!". Then we define a string str equal to "Wo" and use the indexOf() method to find the first occurrence of the substring "Wo" in the string. Finally, we print the results.

The output result is:

子字符串 'Wo' 第一次出现的位置：6

It should be noted that the index returned by the indexOf() method is the starting position of the substring in the string. If the specified character or substring cannot be found, String, will return -1.

Through the above example code, we can see that using the indexOf() method of the StringBuilder class can easily find a specified character or substring in a string and obtain its position in the string. This is very useful when dealing with text, string replacement and other needs. I hope this article will help you understand and use the indexOf() method of the StringBuilder class in Java.

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