Extending enum in Java

Question

public enum myEnum {    
VAL1(10), VAL2(20), VAL3("hai") {
        public Object getValue() {
            return this.strVal;
        }
        public String showMsg() {
            return "This is your msg!";
        }
    };
    String strVal;
    Integer intVal;
    public Object getValue() {
        return this.intVal;
    }
    private myEnum(int i) {
        this.intVal = new Integer(i);
    }
    private myEnum(String str) {
        this.strVal = str;
    }
}

In the above enum what exactly happens when I add a constant specific class body for VAL3?

The type of VAL3 is definetly a subtype of myEnum as it has overloaded and additional methods. (the class type comes as 'myEnum$1' )

But how can the compiler creates a subtype enum extending myEnum as all the enums are already extending java.lang.enum ?

Just to mention another point here: The method VAL3.showMsg() won't be visible outside of VAL3. Only methods that are declared in the enum type can be used outside, linke myEnum.getValue(). This means, there is no point in declaring individual public methods that were not defined before in the enum type. Of course, you can define arbitrary helper methods in each enum value, but you should keep in mind that they are not accessible from outside. Make helper methods private to make this clear to the reader of your code. — migu
– migu, Commented Jan 16, 2012 at 10:10

Craig P. Motlin · Accepted Answer · 2008-11-26 04:08:16Z

5

Your class myEnum inherits from java.lang.Enum. VAL3 is an anonymous inner class that inherits from myEnum called myEnum$1. 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 or myEnum directly.

answered Nov 26, 2008 at 4:08

Craig P. Motlin

26.8k18 gold badges105 silver badges128 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

2 revs, 2 users 99% geeeeeeeeeek · Accepted Answer · 2008-11-26 11:47:10Z

From decompiler


package com.sun.tools.xjc.outline;


public final class Aspect extends Enum
{
    public static final Aspect EXPOSED;
    public static final Aspect IMPLEMENTATION;
    private static final Aspect $VALUES[];

    static 
    {
        EXPOSED = new Aspect("EXPOSED", 0);
        IMPLEMENTATION = new Aspect("IMPLEMENTATION", 1);
        $VALUES = (new Aspect[] {
            EXPOSED, IMPLEMENTATION
        });
    }

    public static final Aspect[] values()
    {
        return (Aspect[])$VALUES.clone();
    }

    public static Aspect valueOf(String name)
    {
        Aspect arr$[] = $VALUES;
        int len$ = arr$.length;
        for(int i$ = 0; i$ < len$; i$++)
        {
            Aspect aspect = arr$[i$];
            if(aspect.name().equals(name))
                return aspect;
        }

        throw new IllegalArgumentException(name);
    }

    private Aspect(String s, int i)
    {
        super(s, i);
    }


}

Collectives™ on Stack Overflow

Extending enum in Java

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related