Java indexOf not found

The indexOf method in Java allows the programmer to search for a specified substring or character within a string. However, if the substring or character is not found, the indexOf method returns -1.

Syntax

The syntax for the indexOf method is as follows:

public int indexOf(String str)                 // searching for a substring
public int indexOf(int ch)                     // searching for a character
public int indexOf(String str, int fromIndex)  // searching for a substring starting from a specific index
public int indexOf(int ch, int fromIndex)      // searching for a character starting from a specific index

In all cases, if the specified substring or character is not found in the original string, the indexOf method returns -1.

Example

Here is an example of using the indexOf method to search for a substring in a string:

String message = "Java is a popular programming language";
int index = message.indexOf("programming");

if (index != -1) {
  System.out.println("Substring found at index " + index);
} else {
  System.out.println("Substring not found");
}

In this example, the indexOf method is used to search for the substring "programming" in the message string. If the substring is found, the method returns the index of the first occurrence of the substring. If the substring is not found, the method returns -1.

Handling "indexOf not found"

If the indexOf method returns -1, this means that the specified substring or character was not found in the original string. As a programmer, you should handle this case appropriately in your code.

One approach is to check the return value and take some action based on whether the substring or character was found or not. For example, you could display an error message to the user or return a default value.

Another approach is to use the contains method instead of indexOf. The contains method returns a boolean value indicating whether the specified substring or character is present in the original string. This can simplify your code in cases where you only need to check for the presence of a substring or character, rather than its exact location within the string.

Conclusion

The indexOf method in Java is a useful tool for searching for substrings and characters within strings. However, it is important to handle the case where the substring or character is not found, which can be indicated by a return value of -1.