Java Program: Lambda expression for checking uppercase, lowercase, or mixedcase strings

Last update on May 09 2025 12:49:07 (UTC/GMT +8 hours)

22. Check case of strings in list using lambda

Write a Java program to implement a lambda expression to check if a list of strings are all uppercase or all lowercase or mixedcase.

Sample Solution:

Java Code:

import java.util.Arrays;
import java.util.List;
import java.util.function.Predicate;
import java.util.function.Function;

public class Main {
  public static void main(String[] args) {
    List < String > strings = Arrays.asList("Java", "JAVA", "java");
    System.out.println("Array elements: " + strings);
    // Check if the list is all uppercase using lambda expression
    boolean isAllUppercase = checkCase(strings, s -> s.equals(s.toUpperCase()), String::toUpperCase);
    System.out.println("Is all uppercase? " + isAllUppercase);

    // Check if the list is all lowercase using lambda expression
    boolean isAllLowercase = checkCase(strings, s -> s.equals(s.toLowerCase()), String::toLowerCase);
    System.out.println("Is all lowercase? " + isAllLowercase);

    // Check if the list is mixed case
    boolean isMixedCase = !isAllUppercase && !isAllLowercase;
    System.out.println("Is mixed case? " + isMixedCase);

    List < String > strings1 = Arrays.asList("JAVA", "PYTHON", "ABC");
    System.out.println("\nArray elements: " + strings1);
    // Check if the list is all uppercase using lambda expression
    isAllUppercase = checkCase(strings1, s -> s.equals(s.toUpperCase()), String::toUpperCase);
    System.out.println("Is all uppercase? " + isAllUppercase);

    // Check if the list is all lowercase using lambda expression
    isAllLowercase = checkCase(strings1, s -> s.equals(s.toLowerCase()), String::toLowerCase);
    System.out.println("Is all lowercase? " + isAllLowercase);

    // Check if the list is mixed case
    isMixedCase = !isAllUppercase && !isAllLowercase;
    System.out.println("Is mixed case? " + isMixedCase);

    List < String > strings2 = Arrays.asList("java");
    System.out.println("\nArray elements: " + strings2);
    // Check if the list is all uppercase using lambda expression
    isAllUppercase = checkCase(strings2, s -> s.equals(s.toUpperCase()), String::toUpperCase);
    System.out.println("Is all uppercase? " + isAllUppercase);

    // Check if the list is all lowercase using lambda expression
    isAllLowercase = checkCase(strings2, s -> s.equals(s.toLowerCase()), String::toLowerCase);
    System.out.println("Is all lowercase? " + isAllLowercase);

    // Check if the list is mixed case
    isMixedCase = !isAllUppercase && !isAllLowercase;
    System.out.println("Is mixed case? " + isMixedCase);

  }
  public static boolean checkCase(List < String > strings, Predicate < String > checkFunction, Function < String, String > convertFunction) {
    String firstString = strings.get(0);
    String convertedString = convertFunction.apply(firstString);

    return strings.stream()
      .allMatch(s -> checkFunction.test(s));
  }
}

Sample Output:

Array elements: [Java, JAVA, java]
Is all uppercase? false
Is all lowercase? false
Is mixed case? true

Array elements: [JAVA, PYTHON, ABC]
Is all uppercase? true
Is all lowercase? false
Is mixed case? false

Array elements: [java]
Is all uppercase? false
Is all lowercase? true
Is mixed case? false

Explanation:

In the above exercise -

The main() method:

• Creates a list of strings named strings.
• Calls the checkCase method to perform case checks and prints the results.

The checkCase() method:

• Takes three parameters: the list of strings to check, a Predicate<String> to define the case check condition, and a Function<String, String> to convert the first string for comparison.
• Retrieves the first string from the list using strings.get(0) and assigns it to firstString.
• Apply the conversion function convertFunction to firstString and assign the result to convertedString.
• Use the stream() method in the strings list to create a stream of strings.
• Apply the allMatch intermediate operation on the stream and provide a lambda expression as the condition to check if all strings satisfy the given predicate checkFunction.
• Returns the result of the allMatch operation, which indicates whether all strings in the list pass the case check.

Flowchart:

For more Practice: Solve these Related Problems:

• Write a Java program to implement a lambda expression that checks if every string in a list is uppercase using allMatch().
• Write a Java program to create a lambda that validates whether all strings in a list are lowercase and returns a boolean result.
• Write a Java program to implement a lambda expression that determines if a list of strings is mixed-case by comparing counts of uppercase and lowercase letters.
• Write a Java program to chain lambda expressions to group strings by their case type and then check for uniformity.

Go to:

• Java Lambda Exercises Home ↩
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