How to check if a String contains only ASCII?

Checking if a string contains only ASCII characters can be done using various methods, depending on the programming language used. Below, I will provide examples for two common programming languages: Python and Java.

Python Example

In Python, we can use the built-in string method isascii() to check. This method returns a boolean value indicating whether the string contains only ASCII characters.

python
def is_ascii(s):
    return s.isascii()

# Example usage
test_str = "Hello, World!"
print(is_ascii(test_str))  # Output: True
test_str2 = "你好，世界！"
print(is_ascii(test_str2))  # Output: False

This method was introduced in Python 3.7 and above, and it is intuitive and easy to use.

Java Example

In Java, there is no direct method to detect whether a string contains only ASCII characters, but we can achieve this by checking the ASCII values of each character in the string. The ASCII character encoding range is 0 to 127.

java
public class Main {
    public static boolean isAscii(String s) {
        for (int i = 0; i < s.length(); i++) {
            if (s.charAt(i) > 127) {
                return false;
            }
        }
        return true;
    }

    public static void main(String[] args) {
        String testStr = "Hello, World!";
        System.out.println(isAscii(testStr));  // Output: true

        String testStr2 = "你好，世界！";
        System.out.println(isAscii(testStr2));  // Output: false
    }
}

In this Java example, we iterate through each character in the string, using charAt() to get the character, and check if its integer value exceeds 127. If all characters fall within the ASCII range, the function returns true.

Summary

Checking if a string contains only ASCII characters is a common requirement, especially when handling internationalized data and ensuring data compatibility. Python provides a very convenient method, while in Java, manual checking of each character is required. Both methods are effective, and the choice depends on your specific needs and the programming language used.