Flash cards
Review the key moves
What is the main idea behind Java Enums?
Lesson checks
Practice each idea before moving on
Short Mimo-style checks built from this lesson's code, terms, and sequence.
Which statement best captures the main point of this lesson?
Complete the missing token from the example code.
___ Level {Put the learning moves in the order that makes the concept easiest to apply.
Enums
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:
enum Level {
LOW, MEDIUM, HIGH
}Enum is short for "enumerations", which means "specifically listed".
Enum inside a Class
You can also have an enum inside a class:
Example
public class Main {
enum Level {
LOW, MEDIUM, HIGH
}
public static void main(String[] args) {
Level myVar = Level.MEDIUM;
System.out.println(myVar);
}
}Enum in a Switch Statement
Enums are often used in switch statements to check for corresponding values:
Example
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;
}
}
}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:
Example
for (Level myVar : Level.values()) {
System.out.println(myVar);
}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).
Use enums when you have values that you know aren't going to change, like month days, days, colors, deck of cards, etc.