What are enums in Java?
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An enum is a special class that represents a group of constants.
Enum keyword is used to create an enum. The constants declared inside are separated by a comma and should be in upper case.
Example
An enum can be declared inside a class or outside a class. In the example below, we are declaring it inside a class:
class MyClass {
enum color { // declaring an enum using the enum keyword
// defining enum constants using the enum keyword
RED,
GREEN,
BLUE
}
public static void main(String[] args) {
color x = color.GREEN; // storing
System.out.println(x);
}
}Properties of enum
- Similar to a class, an
enumcan have objects and methods. The only difference is thatenumconstants arepublic,staticandfinalby default. Since it isfinal, we can’t create child enums - It cannot extend other classes since it already extends the
java.lang.Enumclass. - It can implement interfaces.
- The
enumobjects cannot be created explicitly and hence theenumconstructor cannot be invoked directly. - It can only contain concrete methods and no abstract methods.
Where to use enum?
enum is used for values that are not going to change e.g. names of days, colors in a rainbow, number of cards in a deck etc.
enum is commonly used in switch statements and below is an example of it:
class MyClass {
enum color { // declaring an enum using the enum keyword
// defining enum constants using the enum keyword
RED,
GREEN,
BLUE
}
public static void main(String[] args) {
color x = color.GREEN; // storing value
switch(x) {
case RED:
System.out.println("x has RED color");
break;
case GREEN:
System.out.println("x has GREEN color");
break;
case BLUE:
System.out.println("x has BLUE color");
break;
}
}
}RELATED TAGS
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Ace your System Design Interview and take your career to the next level. Learn to handle the design of applications like Netflix, Quora, Facebook, Uber, and many more in a 45-min interview. Learn the RESHADED framework for architecting web-scale applications by determining requirements, constraints, and assumptions before diving into a step-by-step design process.
