Enumerator question

[Sumukh Deshpande]

Can you please explain why the below code outputs

CONSTANT_1
CONSTANT_2



and not just CONSTANT_1 ?

/**
 * @(#)TestConstructors.java
 *
 *
 * @author
 * @version 1.00 2011/3/30
 */
enum Enumerator{
    	CONSTANT_1(1), CONSTANT_2(2);
    	Enumerator(int a){

    	}

    }
public class TestConstructors {

    /**
     * Creates a new instance of <code>TestConstructors</code>.
     */
    public TestConstructors() {
    	return ;
    }

	Enumerator enumerator;
	public void setEnumerator(Enumerator enumerator){
		this.enumerator = enumerator;
	}

	public Enumerator getEnumerator(){
		return this.enumerator;
	}


    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        
        TestConstructors tc = new TestConstructors();
        tc.setEnumerator(Enumerator.CONSTANT_1);

        Enumerator[] enumsvalues = tc.getEnumerator().values();
        for (Enumerator enums : enumsvalues){
			System.out.println(enums);
        }


    }
}

[Stephan van Hulst]

Hi Sumukh,

values() is a static method of your Enumerator class, that will return all declared enum constants. The fact that you call it on CONSTANT_1 is misleading, since it's a static method.

[Sumukh Deshpande]

Hi Stephan van Hulst,

I understand what you say about values() method.

But is it not that if I am setting the Enumerator through setEnumerator() then the class should have a Enumerator with just CONSTANT_1?

Please correct me if I am wrong.

[Jesper de Jong]

The values() method, that you are calling in line 42 on an instance of Enumerator, is a static method in Enumerator. Do you understand what "static" means? It means that it's a method that works on the whole class, rather than on a specific instance of the class.

You're confused exactly because of the reason that Stephan explains: it's misleading to call static methods on instances, because it looks like it should be doing something with the specific instance, while it is not. Calling values() on a specific instance will not make it work differently from calling it on the class itself.

Rewrite line 42 like this:

Enumerator[] enumsvalues = Enumerator.values();

(I think it's a mistake that Java even allows you to call static methods on instances, because it's too confusing and bad style and isn't useful for anything).

[Stephan van Hulst]

Jesper de Jong wrote:(I think it's a mistake that Java even allows you to call static methods on instances, because it's too confusing and bad style and isn't useful for anything).

Quoted for truth.

[Campbell Ritchie]

I think there were several mistakes like that. Permitting [] after the identifier rather than the type (eg int numbers[]; rather than int[] numbers;) is another, in my opinion.

[Jesper de Jong]

Campbell: That's a feature that Java inherited from C++. When Java was new, it was the intention of the language designers that it looked familiar to C++ programmers. Now we're stuck with this feature forever...

[Stephan van Hulst]

[hijack]Oh man, what I really hate about C is when declaring a pointer type variable the asterisk goes with the variable and not with the type.[/hijack]

[Campbell Ritchie]

Agree, Jesper. They didn't distinguish Java™ from C++ enough in the earlier stages.

[Sumukh Deshpande]

It has cleared my doubt.

I had perfectly misunderstood the values() method.

Thanks a lot all of you.