String toLowerCase and toUpperCase Methods in Java

最后修改: 2023-08-17T06:29:43+00:00

    1. Overview

    In this tutorial, we’ll cover the toUpperCase and toLowerCase methods included in the Java String class.

    We’ll start by creating a String called name:

    String name = "John Doe";

    2. Convert to Uppercase

    To create a new uppercase String based on name, we call the toUpperCase method:

    String uppercaseName = name.toUpperCase();

    This results in uppercaseName having the value “JOHN DOE”:

    assertEquals("JOHN DOE", uppercaseName);

    Note that Strings are immutable in Java and that calling toUpperCase creates a new String. In other words, name is unchanged when calling toUpperCase.

    3. Convert to Lowercase

    Similarly, we create a new lowercase String based on name by calling toLowerCase:

    String lowercaseName = name.toLowerCase();

    This results in lowercaseName having the value “john doe”:

    assertEquals("john doe", lowercaseName);

    Just as with toUpperCase, toLowerCase does not change the value of name.

    4. Change Case Using Locales

    Additionally, by supplying a Locale to the toUpperCase and toLowerCase methods, we can change the case of a String using locale-specific rules.

    For example, we can supply a Locale to uppercase a Turkish i (Unicode 0069):

    Locale TURKISH = new Locale("tr");
System.out.println("\u0069".toUpperCase());
System.out.println("\u0069".toUpperCase(TURKISH));

    Accordingly, this results in an uppercase I and a dotted uppercase I:

    I
İ

    We can verify this using the following assertions:

    assertEquals("\u0049", "\u0069".toUpperCase());
assertEquals("\u0130", "\u0069".toUpperCase(TURKISH));

    Likewise, we can do the same for toLowerCase using the Turkish I (Unicode 0049):

    System.out.println("\u0049".toLowerCase());
System.out.println("\u0049".toLowerCase(TURKISH));

    Consequently, this results in a lowercase i and a lowercase dotless i:

    i
ı

    We can verify this using the following assertions:

    assertEquals("\u0069", "\u0049".toLowerCase());
assertEquals("\u0131", "\u0049".toLowerCase(TURKISH));

    5. Conclusion

    In conclusion, the Java String class includes the toUpperCase and toLowerCase methods for changing the case of a String. If needed, a Locale can be supplied to provide locale-specific rules when changing the case of a String.

    The source code for this article, including examples, can be found over on GitHub.