Use of enum in Java

This article illustrates the use of enums in Java. Share with you for your reference. Specific analysis is as follows:

1. Basic usage

enum Day {

    SUNDAY, MONDAY, TUESDAY, WENDSDAY, THURSDAY, FRIDAY, SATURDAY;

}

Enumerations are constants, so you should use uppercase.

2. Enumeration is an object

Enumeration implicitly inherits from java.lang.enum, so it has the properties and methods of java.lang.enum. Traversal enumeration:

public class Main {

    public static void main(String[] args) {

        for(Day day:Day.values()) {

            System.out.println(day);

        }

    }

}

3. Enumerations can have fields and methods , The following example is from The official The Java™ Tutorials

public enum EnumDemo {

    AOBJECT("field one", "field two");
    private String field1;

    private String field2;
    EnumDemo(String val1, String val2){

        this.field1 = val1;

        this.field2 = val2;

    }
    public void printFields(){

        System.out.println(this.field1);

        System.out.println(this.field2);

    }
    public static void main(String[] args) {

        EnumDemo.AOBJECT.printFields();

    }

}

The following real-world examples are from the official Java Tutorial:

public enum Planet {

    MERCURY (3.303e+23, 2.4397e6),

    VENUS   (4.869e+24, 6.0518e6),

    EARTH   (5.976e+24, 6.37814e6),

    MARS    (6.421e+23, 3.3972e6),

    JUPITER (1.9e+27,   7.1492e7),

    SATURN  (5.688e+26, 6.0268e7),

    URANUS  (8.686e+25, 2.5559e7),

    NEPTUNE (1.024e+26, 2.4746e7);
    private final double mass;   // in kilograms

    private final double radius; // in meters
    Planet(double mass, double radius) {

        this.mass = mass;

        this.radius = radius;

    }
    private double mass() { return mass; }

    private double radius() { return radius; }
    // universal gravitational constant  (m3 kg-1 s-2)

    public static final double G = 6.67300E-11;
    double surfaceGravity() {

        return G * mass / (radius * radius);

    }
    double surfaceWeight(double otherMass) {

        return otherMass * surfaceGravity();

    }
    public static void main(String[] args) {

        Double earthWeight = 120;

        for(Planet p: Planet.values()){

            System.out.println(p.surfaceGravity());

            System.out.println(p.surfaceWeight(earthWeight/EARTH.surfaceGravity()));

        }

    }

}

4. An enumeration is a singleton, and you can use an enumeration to build a singleton

public enum Singleton {

    INSTANCE(new String[]{"arg1", "arg2"});
    String[] myArgs;

    Singleton(String[] args){

        this.myArgs = args;

    }
    public static Singleton getInstance(){

        return INSTANCE;

    }
    public static void main(String[] args) {

        for(String arg : INSTANCE.myArgs)

            System.out.println(arg);

    }

}

I hope this article has been helpful to your Java programming.