Case-insensitive matching of a string to a Java enum

Case-insensitive matching of a string to a Java enum

To perform case-insensitive matching of a string to a Java enum, you can follow these steps:

  1. Define the Enum: Create an enum with the desired values.
  2. Implement Case-Insensitive Matching: Implement a method to handle case-insensitive matching by iterating through enum values and comparing them in a case-insensitive manner.

Example

Let's assume you have an enum called Color:

public enum Color { RED, GREEN, BLUE; }

Here's how you can implement a method to perform case-insensitive matching:

public class EnumUtils { public static Color fromString(String value) { if (value == null) { return null; } for (Color color : Color.values()) { if (color.name().equalsIgnoreCase(value)) { return color; } } throw new IllegalArgumentException("No enum constant for value: " + value); } public static void main(String[] args) { // Test case-insensitive matching System.out.println(fromString("red")); // Output: RED System.out.println(fromString("Green")); // Output: GREEN System.out.println(fromString("bLuE")); // Output: BLUE // Uncommenting the following line will throw an exception // System.out.println(fromString("yellow")); } }

Explanation

  1. fromString Method:

    • Parameter: Takes a String value to match against the enum values.
    • Null Check: If the provided value is null, it returns null.
    • Case-Insensitive Comparison:
      • Iterates through all values of the Color enum.
      • Uses String.equalsIgnoreCase to compare the enum constant's name with the provided value in a case-insensitive manner.
      • If a match is found, returns the corresponding enum constant.
    • Exception Handling: Throws an IllegalArgumentException if no matching enum constant is found.

  2. Testing:

    • Demonstrates how to use the fromString method to match enum values case-insensitively.
    • Shows that providing a non-existing value will result in an exception.

Alternative Approach

If you prefer to keep the enum values and their matching logic encapsulated within the enum itself, you can add a static method to the enum:

public enum Color { RED, GREEN, BLUE; public static Color fromString(String value) { if (value == null) { return null; } for (Color color : Color.values()) { if (color.name().equalsIgnoreCase(value)) { return color; } } throw new IllegalArgumentException("No enum constant for value: " + value); } }

Then you can call it like this:

public class EnumTest { public static void main(String[] args) { System.out.println(Color.fromString("red")); // Output: RED System.out.println(Color.fromString("Green")); // Output: GREEN System.out.println(Color.fromString("bLuE")); // Output: BLUE } }

Summary

  • Enum Definition: Define the enum with its constants.
  • Case-Insensitive Matching: Implement a method that compares string values with enum constants in a case-insensitive way.
  • Usage: Use the method to perform case-insensitive matching of strings to enum constants.

This approach ensures that you can handle case-insensitive string-to-enum mappings efficiently and cleanly.

Examples

  1. How to perform case-insensitive matching of a string to a Java enum value

    Description: Convert the input string to uppercase (or lowercase) and compare it to enum values.

    public enum Color { RED, GREEN, BLUE; } public class Main { public static void main(String[] args) { String input = "green"; Color color = getColorIgnoreCase(input); System.out.println(color); // Output: GREEN } public static Color getColorIgnoreCase(String name) { for (Color color : Color.values()) { if (color.name().equalsIgnoreCase(name)) { return color; } } throw new IllegalArgumentException("No enum constant with text " + name); } }

  2. How to use Java 8 Streams for case-insensitive enum matching

    Description: Use Java 8 Streams to filter enum values based on a case-insensitive match.

    import java.util.Arrays; public enum Color { RED, GREEN, BLUE; } public class Main { public static void main(String[] args) { String input = "blue"; Color color = Arrays.stream(Color.values()) .filter(c -> c.name().equalsIgnoreCase(input)) .findFirst() .orElseThrow(() -> new IllegalArgumentException("No enum constant with text " + input)); System.out.println(color); // Output: BLUE } }

  3. How to handle case-insensitive enum matching with Apache Commons Lang

    Description: Use Apache Commons Lang's EnumUtils for case-insensitive matching.

    import org.apache.commons.lang3.EnumUtils; public enum Color { RED, GREEN, BLUE; } public class Main { public static void main(String[] args) { String input = "red"; Color color = EnumUtils.getEnumIgnoreCase(Color.class, input); System.out.println(color); // Output: RED } }

  4. How to perform case-insensitive enum matching using a Map in Java

    Description: Store enum values in a Map with lowercase keys for case-insensitive lookups.

    import java.util.HashMap; import java.util.Map; public enum Color { RED, GREEN, BLUE; private static final Map<String, Color> lookup = new HashMap<>(); static { for (Color color : Color.values()) { lookup.put(color.name().toLowerCase(), color); } } public static Color getColorIgnoreCase(String name) { return lookup.get(name.toLowerCase()); } } public class Main { public static void main(String[] args) { String input = "GREEN"; Color color = Color.getColorIgnoreCase(input); System.out.println(color); // Output: GREEN } }

  5. How to use a switch statement with case-insensitive enums

    Description: Implement case-insensitive enum matching within a switch statement by normalizing the input.

    public enum Color { RED, GREEN, BLUE; } public class Main { public static void main(String[] args) { String input = "green"; Color color = getColorIgnoreCase(input); switch (color) { case RED: System.out.println("Red color selected."); break; case GREEN: System.out.println("Green color selected."); break; case BLUE: System.out.println("Blue color selected."); break; } } public static Color getColorIgnoreCase(String name) { for (Color color : Color.values()) { if (color.name().equalsIgnoreCase(name)) { return color; } } throw new IllegalArgumentException("No enum constant with text " + name); } }

  6. How to create a utility method for case-insensitive enum matching

    Description: Write a utility method to handle case-insensitive matching for any enum type.

    public class EnumUtils { public static <E extends Enum<E>> E getEnumIgnoreCase(Class<E> enumType, String value) { for (E enumConstant : enumType.getEnumConstants()) { if (enumConstant.name().equalsIgnoreCase(value)) { return enumConstant; } } throw new IllegalArgumentException("No enum constant with text " + value); } } public enum Color { RED, GREEN, BLUE; } public class Main { public static void main(String[] args) { String input = "blue"; Color color = EnumUtils.getEnumIgnoreCase(Color.class, input); System.out.println(color); // Output: BLUE } }

  7. How to use valueOf with case-insensitive matching in Java enums

    Description: Implement a custom valueOf method to handle case-insensitive lookups.

    public enum Color { RED, GREEN, BLUE; public static Color valueOfIgnoreCase(String name) { for (Color color : Color.values()) { if (color.name().equalsIgnoreCase(name)) { return color; } } throw new IllegalArgumentException("No enum constant with text " + name); } } public class Main { public static void main(String[] args) { String input = "RED"; Color color = Color.valueOfIgnoreCase(input); System.out.println(color); // Output: RED } }

  8. How to ensure case-insensitive matching with enums in a large application

    Description: Optimize case-insensitive matching by caching enum values.

    import java.util.HashMap; import java.util.Map; public enum Color { RED, GREEN, BLUE; private static final Map<String, Color> CACHE = new HashMap<>(); static { for (Color color : Color.values()) { CACHE.put(color.name().toLowerCase(), color); } } public static Color getColorIgnoreCase(String name) { return CACHE.get(name.toLowerCase()); } } public class Main { public static void main(String[] args) { String input = "Blue"; Color color = Color.getColorIgnoreCase(input); System.out.println(color); // Output: BLUE } }

  9. How to handle case-insensitive enum matching with external libraries

    Description: Utilize external libraries like google-guava for case-insensitive operations.

    import com.google.common.base.Enums; import com.google.common.base.Optional; public enum Color { RED, GREEN, BLUE; } public class Main { public static void main(String[] args) { String input = "green"; Optional<Color> color = Enums.getIfPresent(Color.class, input.toUpperCase()); System.out.println(color.orElseThrow(() -> new IllegalArgumentException("No enum constant with text " + input))); // Output: GREEN } }

  10. How to handle case-insensitive enum matching in Java using functional programming

    Description: Use Java functional programming concepts for case-insensitive enum matching.

    import java.util.Arrays; import java.util.function.Function; import java.util.stream.Collectors; public enum Color { RED, GREEN, BLUE; private static final Function<String, Color> LOOKUP = Arrays.stream(values()) .collect(Collectors.toMap(c -> c.name().toLowerCase(), c -> c, (a, b) -> a)) .::get; public static Color fromStringIgnoreCase(String name) { return LOOKUP.apply(name.toLowerCase()); } } public class Main { public static void main(String[] args) { String input = "blue"; Color color = Color.fromStringIgnoreCase(input); System.out.println(color); // Output: BLUE } }

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