How to Check If a Character Is Lowercase in Java

Introduction

In this lab, you will learn how to check if a character is lowercase in Java using the Character.isLowerCase() method. You will practice using this method with various characters, including lowercase letters, uppercase letters, digits, and symbols, to understand its behavior.

Through hands-on exercises, you will create a simple Java program to demonstrate the usage of Character.isLowerCase() and observe the boolean output for different character types. This lab will provide a practical understanding of how to determine the case of a character in Java.

Skills Graph

Use Character.isLowerCase() Method

In this step, you will learn how to use the Character.isLowerCase() method in Java. This method is part of the Character class and is used to determine if a given character is a lowercase letter.

The Character.isLowerCase() method takes a single character as an argument and returns a boolean value: true if the character is a lowercase letter, and false otherwise.

Let's create a new Java file to practice using this method.

1. Open the File Explorer on the left side of the WebIDE.

2. Navigate to the ~/project directory.

3. Right-click in the empty space within the ~/project directory and select "New File".

4. Name the new file LowerCaseCheck.java.

5. Open the LowerCaseCheck.java file in the editor.

6. Copy and paste the following code into the editor:

   public class LowerCaseCheck {
       public static void main(String[] args) {
           char char1 = 'a';
           char char2 = 'B';
           char char3 = '5';
           char char4 = '$';
   
           boolean isLower1 = Character.isLowerCase(char1);
           boolean isLower2 = Character.isLowerCase(char2);
           boolean isLower3 = Character.isLowerCase(char3);
           boolean isLower4 = Character.isLowerCase(char4);
   
           System.out.println("Is '" + char1 + "' lowercase? " + isLower1);
           System.out.println("Is '" + char2 + "' lowercase? " + isLower2);
           System.out.println("Is '" + char3 + "' lowercase? " + isLower3);
           System.out.println("Is '" + char4 + "' lowercase? " + isLower4);
       }
   }

   In this code:

   • We declare four char variables, each holding a different character.
   • We use Character.isLowerCase() to check if each character is lowercase and store the result in a boolean variable.
   • We then print the results to the console.

7. Save the file by pressing Ctrl + S (or Cmd + S on Mac).

Now, let's compile and run this program to see the output.

8. Open the Terminal at the bottom of the WebIDE. Ensure you are in the ~/project directory. If not, type cd ~/project and press Enter.

9. Compile the Java file using the javac command:

   javac LowerCaseCheck.java

   If there are no errors, this command will create a LowerCaseCheck.class file in the ~/project directory.

10. Run the compiled Java program using the java command:

    java LowerCaseCheck

    You should see output similar to this:

    Is 'a' lowercase? true
    Is 'B' lowercase? false
    Is '5' lowercase? false
    Is '$' lowercase? false

This output shows that Character.isLowerCase() correctly identified 'a' as lowercase and the other characters as not lowercase.

Test with Various Characters

In the previous step, you learned how to use Character.isLowerCase() with a few examples. Now, let's test this method with a wider range of characters to see how it behaves. Understanding how a method works with different inputs is crucial in programming.

We will modify the LowerCaseCheck.java file we created in the last step to include more test cases.

1. Open the LowerCaseCheck.java file in the WebIDE editor. It should be located in the ~/project directory.

2. Modify the main method to include more characters for testing. Replace the existing code inside the main method with the following:

   public static void main(String[] args) {
       char char1 = 'z'; // Lowercase letter
       char char2 = 'A'; // Uppercase letter
       char char3 = '9'; // Digit
       char char4 = '!'; // Symbol
       char char5 = 'é'; // Lowercase letter with accent (Unicode)
       char char6 = 'Ü'; // Uppercase letter with umlaut (Unicode)
       char char7 = ' '; // Space
   
       System.out.println("Is '" + char1 + "' lowercase? " + Character.isLowerCase(char1));
       System.out.println("Is '" + char2 + "' lowercase? " + Character.isLowerCase(char2));
       System.out.println("Is '" + char3 + "' lowercase? " + Character.isLowerCase(char3));
       System.out.println("Is '" + char4 + "' lowercase? " + Character.isLowerCase(char4));
       System.out.println("Is '" + char5 + "' lowercase? " + Character.isLowerCase(char5));
       System.out.println("Is '" + char6 + "' lowercase? " + Character.isLowerCase(char6));
       System.out.println("Is '" + char7 + "' lowercase? " + Character.isLowerCase(char7));
   }

   We've added more characters, including a lowercase letter at the end of the alphabet ('z'), an uppercase letter at the beginning ('A'), a digit ('9'), a symbol ('!'), and some Unicode characters with accents and umlauts ('é' and 'Ü'). We also included a space character (' ').

3. Save the modified LowerCaseCheck.java file (Ctrl + S or Cmd + S).

Now, let's compile and run the updated program.

4. Open the Terminal at the bottom of the WebIDE. Ensure you are in the ~/project directory.

5. Compile the modified Java file:

   javac LowerCaseCheck.java

   Again, if the compilation is successful, you won't see any output.

6. Run the compiled Java program:

   java LowerCaseCheck

   Observe the output. It should look something like this:

   Is 'z' lowercase? true
   Is 'A' lowercase? false
   Is '9' lowercase? false
   Is '!' lowercase? false
   Is 'é' lowercase? true
   Is 'Ü' lowercase? false
   Is ' ' lowercase? false

   Notice that Character.isLowerCase() correctly identifies 'z' and 'é' as lowercase letters, while 'A', '9', '!', 'Ü', and ' ' are not considered lowercase letters by this method. This demonstrates that the method works for a variety of characters, including some non-ASCII letters.

Handle Non-Letter Characters

In the previous steps, you've seen how Character.isLowerCase() works with both lowercase and uppercase letters, as well as some non-letter characters like digits, symbols, and spaces. It's important to remember that Character.isLowerCase() is specifically designed to check for lowercase letters. It will return false for any character that is not considered a letter in the Unicode standard, regardless of whether it appears in a "lowercase" form (like a lowercase digit, which doesn't exist).

Let's create a slightly different program that focuses on checking various non-letter characters to reinforce this understanding.

1. Open the File Explorer on the left side of the WebIDE.

2. Navigate to the ~/project directory.

3. Right-click in the empty space within the ~/project directory and select "New File".

4. Name the new file NonLetterCheck.java.

5. Open the NonLetterCheck.java file in the editor.

6. Copy and paste the following code into the editor:

   public class NonLetterCheck {
       public static void main(String[] args) {
           char digit = '7';
           char symbol = '#';
           char space = ' ';
           char newline = '\n'; // Newline character
           char tab = '\t';   // Tab character
   
           System.out.println("Is '" + digit + "' lowercase? " + Character.isLowerCase(digit));
           System.out.println("Is '" + symbol + "' lowercase? " + Character.isLowerCase(symbol));
           System.out.println("Is ' ' lowercase? " + Character.isLowerCase(space));
           System.out.println("Is newline lowercase? " + Character.isLowerCase(newline));
           System.out.println("Is tab lowercase? " + Character.isLowerCase(tab));
       }
   }

   In this program, we are explicitly testing characters that are not letters: a digit, a symbol, a space, a newline character (\n), and a tab character (\t).

7. Save the file (Ctrl + S or Cmd + S).

Now, compile and run this new program.

8. Open the Terminal at the bottom of the WebIDE. Ensure you are in the ~/project directory.

9. Compile the Java file:

   javac NonLetterCheck.java

10. Run the compiled Java program:

    java NonLetterCheck

    You should see the following output:

    Is '7' lowercase? false
    Is '#' lowercase? false
    Is ' ' lowercase? false
    Is newline lowercase? false
    Is tab lowercase? false

    As expected, Character.isLowerCase() returns false for all these non-letter characters. This confirms that the method is specifically for checking if a character is a lowercase letter.

Understanding the behavior of methods like Character.isLowerCase() with different types of input is fundamental to writing correct and predictable code. In the next steps, you might explore other methods in the Character class, such as isUpperCase(), isDigit(), or isLetter().

Summary

In this lab, you learned how to check if a character is lowercase in Java using the Character.isLowerCase() method. You practiced using this method by creating a Java file, writing code to test various characters (lowercase letters, uppercase letters, digits, and symbols), and printing the boolean results to the console. This hands-on exercise demonstrated the basic usage of Character.isLowerCase() and how it distinguishes between lowercase letters and other character types.