Java Перерахування
Enums / Перерахування
An enum is a special "class" that represents a group of constants (unchangeable variables, like final variables).
To create an enum, use the enum keyword (instead of class or interface), and separate the constants with a comma. Note that they should be in uppercase letters:
Приклад
enum Level {
LOW,
MEDIUM,
HIGH
}
You can access enum constants with the dot syntax:
Level myVar = Level.MEDIUM;
Спробуйте самі »
Enum is short for "enumerations", which means "specifically listed".
Enum inside a Class
You can also have an enum inside a class:
Приклад
public class Main {
enum Level {
LOW,
MEDIUM,
HIGH
}
public static void main(String[] args) {
Level myVar = Level.MEDIUM;
System.out.println(myVar);
}
}
Виведення буде:
MEDIUM
Enum in a Switch Statement
Enums are often used in switch statements to check for corresponding values:
Приклад
enum Level {
LOW,
MEDIUM,
HIGH
}
public class Main {
public static void main(String[] args) {
Level myVar = Level.MEDIUM;
switch(myVar) {
case LOW:
System.out.println("Low level");
break;
case MEDIUM:
System.out.println("Medium level");
break;
case HIGH:
System.out.println("High level");
break;
}
}
}
Виведення буде:
Medium level
Loop Through an Enum
The enum type has a values() method, which returns an array of all enum constants. This method is useful when you want to loop through the constants of an enum:
Приклад
for (Level myVar : Level.values()) {
System.out.println(myVar);
}
The output will be:
LOW
MEDIUM
HIGH
Difference between Enums and Classes
An enum can, just like a class, have attributes and methods. The only difference is that enum constants are public, static and final (unchangeable - cannot be overridden).
An enum cannot be used to create objects, and it cannot extend other classes (but it can implement interfaces).
Why And When To Use Enums?
Use enums when you have values that you know aren't going to change, like month days, days, colors, deck of cards, etc.
