How to extends Enum in Java?

Question

I have a class from sample project.But when I am using this class it shows some errors.The class is given below.

public  class q extends Enum
{

    private int i = -1;
    private String s = null;

    private q(String s, int i)
    {
       // super(s, i);
        this.s = s;
        this.i  = i;
    }

    public static q valueOf(String s)
    {
        return (q)Enum.valueOf(q.class, s);
    }

    public static q[] values()
    {
        return (q[])a.clone();
    }

    public static final q ANDROID_VERSION;
    public static final q APP_VERSION_CODE;
    public static final q APP_VERSION_NAME;
    public static final q AVAILABLE_MEM_SIZE;
    private static final q a[];

    static 
    {
        APP_VERSION_CODE = new q("APP_VERSION_CODE", 1);
        APP_VERSION_NAME = new q("APP_VERSION_NAME", 2);
        ANDROID_VERSION = new q("ANDROID_VERSION", 6);
        AVAILABLE_MEM_SIZE = new q("AVAILABLE_MEM_SIZE", 11);
        q aq[] = new q[34];
        aq[0] = APP_VERSION_CODE;
        aq[1] = ANDROID_VERSION;
        aq[2] = APP_VERSION_NAME;
        aq[3] = AVAILABLE_MEM_SIZE;
        a = aq;
    }

}

When extending Enum it shows "The type q may not subclass Enum explicitly" error.How can i create an enum using these fields?

How can i modify this class to use like enum(ie,I want to use the default enum methods like ordinal(),valueOf(...) etc.. on this.)?

Answer 1

You cannot extend from Enum. You have to declare an Enum class like:

public enum Q {
    TYPE1, TYPE2, TYPE3;
}

And you also cannot instantiate an enum class directly. Each type of your enum class is instantiated exactly once by the virtual machine.

public class MyClass {

    public enum MyEnum{
        TYPE1("Name", 9,1,100000), TYPE2("Name2", 10, 1, 200000);

        private final int androidVersion;
        private final int appVersionCode;
        private final int availableMemSize;
        private final String appVersionName;

        private MyEnum(String appVersionName, int androidVersion, int appVersionCode, int availableMemSize) {
            this.androidVersion = androidVersion;
            this.appVersionCode = appVersionCode;
            this.availableMemSize = availableMemSize;
            this.appVersionName = appVersionName;
        }
    }
    MyEnum mType = MyEnum.TYPE1;
}

Answer 2

Enums basically boil down to something like this:

public Enum Q
{
    TYPE1, TYPE2, TYPE3:
}

// is roughy translated to 

public final class Q
{
    private Q() {}

    public static final Q TYPE1 = new Q();
    public static final Q TYPE2 = new Q();
    public static final Q TYPE3 = new Q();
}

There is more you can do, but this should explain why you can not instantiate Q.

Answer 3

- Think of the enum keyword as syntatic sugar. It sets up classes with normal inheritance trees for you, but will not allow you to extend java.lang.Enum.

Eg:

public enum TEST {  
    ONE, TWO, THREE;
}