Java String toUpperCase() method

The toUpperCase() method in Java is used to convert all characters in a string to uppercase. This method returns a new string where all alphabetic characters are converted to their uppercase form, while other characters (non-alphabetic) remain unchanged.

Syntax:

str.toUpperCase()  // where str is a string value

Note: Converts all characters of the string to uppercase based on the default locale.

When we use locale for this method.

str.toUpperCase(locale)  // where str is a string value

Note: Converts all characters to uppercase based on the rules of the specified Locale. This is particularly useful for non-English languages where uppercase conversion rules might differ.

Important Points

1. The method does not modify the original string; it returns a new string with the characters converted to uppercase.
2. The method does not affect non-alphabetic characters (like numbers, spaces, or punctuation).
3. The toUpperCase() method is locale-sensitive, meaning that it can respect regional differences in uppercase conversion if you use the version that accepts a Locale.

Example:

public class StringUpperCaseExample {
    public static void main(String[] args) {
        String str = "Hello, World!";
        
        // Convert string to uppercase
        String upperStr = str.toUpperCase();
        
        System.out.println("Original String: " + str);  // Output: Hello, World!
        System.out.println("Uppercase String: " + upperStr);  // Output: HELLO, WORLD!
    }
}

Output:

Using toUpperCase(Locale locale)

import java.util.Locale;

public class ToUpperCaseExample {
    public static void main(String[] args) {
        String str = "hello world!";
        
        // Convert string to uppercase using a specific Locale (e.g., turkish)
        String upperStr = str.toUpperCase(Locale.forLanguageTag("tr"));
        
        System.out.println("Original String: " + str);  // Output: hello world!
        System.out.println("Uppercase String (Turkish Locale): " + upperStr);  // Output: HELLO WORLD!
    }
}

Output: