How to Check If a String Contains a Substring Ignoring Case in Java?

How do I determine if a string in Java includes a substring, ignoring case sensitivity?

public boolean containsIgnoreCase(String str1, String str2) {
    return str1.toLowerCase().contains(str2.toLowerCase());
}

In Java, checking if a string contains a substring without considering case can be achieved using various methods. The most straightforward way involves converting both strings to the same case (either lower or upper) and then checking for the containment using the `contains` method. This approach maintains clarity and efficiency while ensuring case insensitivity.

// Java method to check if str2 is in str1, ignoring case
public boolean containsIgnoreCase(String str1, String str2) {
    // Convert both strings to lower case and check containment
    return str1.toLowerCase().contains(str2.toLowerCase());
}

Causes

• Using `contains()` without normalizing cases will lead to incorrect results if the cases do not match.
• Mismatched delimiters or whitespace can affect substring checks if not appropriately handled.

Solutions

• Utilize the `toLowerCase()` or `toUpperCase()` methods to standardize both strings before the check.
• Consider using Regular Expressions for more complex cases of substring checks.

Mistake: Not normalizing the case of both strings before comparison.

Solution: Always convert both strings to either lower case or upper case before using the `contains()` method.

Mistake: Assuming `contains()` works without case sensitivity by default.

Solution: Understand that Java's `contains()` method is case-sensitive unless normalized.