Java enums are a powerful feature that allows developers to create a set of predefined constants that can be used in their code. Enum constants are essentially a special type of class that have a fixed set of instances, also known as enum values. These values can be accessed and used in a variety of ways, making enums a valuable tool for any Java developer.
One of the useful methods available for enums is the valueOf() method. This method allows you to retrieve an enum constant based on its name. In this article, we will explore the valueOf() method in more detail and see how it can be used with enums that have multiple values.
To start off, let's first understand the basics of enums. Enums were introduced in Java 5 as a way to represent a set of constants in a more structured and type-safe manner. Enum constants are declared using the enum keyword and are typically placed at the top of a class, outside of any method.
For example, we can define an enum called "Days" that represents the days of the week, like this:
enum Days {
MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY, SUNDAY
}
Now, let's say we want to retrieve the enum constant for Monday. This is where the valueOf() method comes in. The valueOf() method takes in a String parameter and returns the corresponding enum constant if it exists. In our case, we can use it like this:
Days monday = Days.valueOf("MONDAY");
The valueOf() method will throw an IllegalArgumentException if the provided String does not match any of the enum constants. So, for example, if we try to retrieve the enum constant for "MONDAYS" instead of "MONDAY", we will get an exception.
Now, let's see how the valueOf() method works with enums that have multiple values. Consider the following enum called "Colors" that has three values - RED, GREEN, and BLUE:
enum Colors {
RED, GREEN, BLUE
}
If we try to retrieve the enum constant for RED using the valueOf() method, it will work just like before. But what if we want to retrieve the enum constant for a combination of colors, like RED and BLUE?
This is where the valueOf() method shows its true power. With enums that have multiple values, the valueOf() method can take in a comma-separated list of enum constants and return a set of all the matching constants.
So, in our example, we can use the valueOf() method like this to get a set containing the RED and BLUE enum constants:
Set<Colors> redAndBlue = EnumSet.allOf(Colors.class).stream()
.filter(c -> c.name().contains("RED") || c.name().contains("BLUE"))
.collect(Collectors.toSet());
Here, we are using the EnumSet class, which is a specialized Set implementation for enum types, to get all the constants of the Colors enum. Then, we filter out the constants that contain the strings "RED" or "BLUE" in their name and collect them into a set.
This can be particularly useful in situations where you want to perform operations on a specific subset of enum constants. For example, if you have an enum that represents different types of users and you want to perform certain actions only on admin and manager users, you can use the valueOf() method to get a set of those specific constants.
In conclusion, the valueOf() method is a handy tool for working with enums in Java, especially when dealing with enums that have multiple values. It allows you to retrieve enum constants based on their names and even get a set of constants by providing a list of names. So, the next time you are working with enums in your Java code, remember to make use of the valueOf() method for convenient and efficient handling of enum constants.
