Java Enumerations, also known as "enums," are a special type of class that represent a fixed set of predefined constants. The enum type is defined using the "enum" keyword, and the constants are defined as instances of the enum type. One of the useful methods provided by the Enum class is the "valueOf()" method. This method returns the enum constant of the specified enum type with the specified name. In this article, we will explore the use of the "valueOf()" method with code examples.
The "valueOf()" method is a static method of the Enum class, which means it can be called directly on the enum type without creating an instance of the enum. The method takes a single parameter, which is the name of the enum constant you want to retrieve. The name of the enum constant must match the name of the enum constant that was defined in the enum type.
Here's an example of an enum type called "DaysOfWeek" that represents the days of the week:
enum DaysOfWeek {
MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY, SUNDAY
}
To retrieve the enum constant "MONDAY" from the "DaysOfWeek" enum type, you can use the "valueOf()" method like this:
DaysOfWeek day = Enum.valueOf(DaysOfWeek.class, "MONDAY");
Alternatively, you can also use the enum type name as a static import and call the valueOf method directly on the enum type:
import static DaysOfWeek.valueOf;
...
DaysOfWeek day = valueOf("MONDAY");
It's important to note that if you pass an invalid name to the "valueOf()" method, it will throw a "IllegalArgumentException" exception. For example, if you try to retrieve a constant with the name "NotADay" from the "DaysOfWeek" enum type, the following code will throw an exception:
DaysOfWeek day = Enum.valueOf(DaysOfWeek.class, "NotADay");
To avoid this exception, you can use the "contains()" method of the EnumSet class to check if the enum type contains a constant with the specified name.
if (EnumSet.of(DaysOfWeek.class).contains(name)) {
DaysOfWeek day = Enum.valueOf(DaysOfWeek.class, name);
}
You can also use try-catch block to catch this exception and handle it accordingly.
try {
DaysOfWeek day = Enum.valueOf(DaysOfWeek.class, name);
} catch (IllegalArgumentException e) {
// handle the exception
}
In conclusion, the "valueOf()" method of the Enum class provides a convenient way to retrieve an enum constant by its name. It's important to remember that the method throws an exception if the specified name does not match any of the enum constants. It's also important to check if the specified name is valid before calling the valueOf method to avoid exception.
In addition to the "valueOf()" method, the Enum class also provides several other useful methods for working with enum types.
The "name()" method returns the name of the enum constant as a string. For example, the following code will print "MONDAY":
DaysOfWeek day = DaysOfWeek.MONDAY;
System.out.println(day.name());
The "ordinal()" method returns the position of the enum constant in the enum type. The first constant is at position 0, the second at position 1, and so on. For example, the following code will print "0":
DaysOfWeek day = DaysOfWeek.MONDAY;
System.out.println(day.ordinal());
The "values()" method returns an array of all the enum constants in the enum type, in the order they were declared. For example, the following code will print all the days of the week:
for (DaysOfWeek day : DaysOfWeek.values()) {
System.out.println(day);
}
The Enum class also provides the "compareTo()" method, which compares the enum constants based on their ordinal value. The method returns a negative integer if the current enum constant has a lower ordinal value than the one passed as the parameter, zero if they have the same ordinal value, and a positive integer if the current enum constant has a higher ordinal value.
You can also define fields and methods for an enum type just like a class. For example, you can add a field to the DaysOfWeek enum to represent the number of hours worked on that day and a method to calculate the total hours worked in a week as follows:
enum DaysOfWeek {
MONDAY(8), TUESDAY(8), WEDNESDAY(8), THURSDAY(8), FRIDAY(8), SATURDAY(0), SUNDAY(0);
private int hours;
DaysOfWeek(int hours){
this.hours = hours;
}
public int getHours(){
return this.hours;
}
public static int getTotalHoursWorked(DaysOfWeek[] days){
int total = 0;
for (DaysOfWeek day : days) {
total += day.getHours();
}
return total;
}
}
In addition to the Enum class, Java also provides the EnumSet and EnumMap classes, which are specialized collections for working with enum types. The EnumSet class is a high-performance set implementation for enums, while the EnumMap class is a high-performance map implementation for enums. Both classes provide a more efficient and convenient way to work with enums compared to using a standard Set or Map.
In this article, we have covered the basic usage of the "valueOf()" method of the Enum class and other useful methods provided by the Enum class. We also discussed how to define fields and methods for an enum type and also how to use EnumSet and EnumMap classes for working with enum types efficiently.
Popular questions
Q: What is the purpose of the "valueOf()" method in Java enums?
A: The "valueOf()" method of the Enum class is used to retrieve an enum constant by its name. It returns the enum constant of the specified enum type with the specified name.
Q: How do you use the "valueOf()" method to retrieve an enum constant?
A: The "valueOf()" method is a static method of the Enum class, which means it can be called directly on the enum type without creating an instance of the enum. The method takes a single parameter, which is the name of the enum constant you want to retrieve. For example:
DaysOfWeek day = Enum.valueOf(DaysOfWeek.class, "MONDAY");
Q: What exception is thrown if an invalid name is passed to the "valueOf()" method?
A: If an invalid name is passed to the "valueOf()" method, it will throw a "IllegalArgumentException" exception.
Q: How can you avoid the exception thrown by the "valueOf()" method when an invalid name is passed?
A: To avoid the exception thrown by the "valueOf()" method, you can use the "contains()" method of the EnumSet class to check if the enum type contains a constant with the specified name, or use try-catch block to catch the exception and handle it accordingly.
Q: What are some other useful methods provided by the Enum class for working with enums?
A: Some other useful methods provided by the Enum class include "name()" which returns the name of the enum constant as a string, "ordinal()" which returns the position of the enum constant in the enum type, "values()" which returns an array of all the enum constants in the enum type, and "compareTo()" which compares the enum constants based on their ordinal value.
Tag
Enumerations.
