Re: Using enums to avoid using switch/if

From:
Lew <lew@lewscanon.com>
Newsgroups:
comp.lang.java.programmer
Date:
Tue, 23 Mar 2010 07:15:37 -0700 (PDT)
Message-ID:
<a2d003a4-674b-48f4-a8d9-5f34aa3bc6c0@z11g2000yqz.googlegroups.com>
Lew quoted or indirectly quoted someone who said :

I need a mechanism to map string to enum.


Why do you not attribute the quote to the one who actually wrote it?

Roedy Green wrote:

see the built-in valueOf function. I often override it to make it
case insensitive and allow aliases.


I doubt that very much. Static methods cannot be overridden.

While there is some value in hiding the 'valueOf' method, I prefer to
use a differently-named method for the same purpose. I am loathe to
(apparently) change the behavior of such a standard, language-defined
method as 'Enum.valueOf'. Instead I use a static 'fromString()'
method to be the companion for 'toString'.

The 'Enum' Javadocs suggest that '[a]n enum type should override
[toString] when a more "programmer-friendly" string form exists.' I
find it mnemonic and symmetrical to go from "programmer-friendly"
string form to enum constant with 'fromString'. This also preserves
the semantics of 'valueOf' as documented in the JLS. Furthermore, I
use 'valueOf' as the fallback if 'fromString' is otherwise unable to
locate the enum constant.

My enum template is:

/* ${name}.java
 */
package ${package};

/**
 * ${name}.
 */
public enum ${name}
{

    private final String repr; // "friendly" representation
    /**
     * Constructor.
     * @param rep String representation of enum value.
     */
    ${name}( String rep )
    {
        this.repr = rep;
    }

    @Override
    public final String toString()
    {
        return this.repr;
    }

    /**
     * Look up enum constant from String representation.
     * @param rep String representation of enum value.
     * @return ${name} constant matching the representation.
     */
    public static ${name} fromString( final String rep )
    {
        if ( rep == null )
        {
            return null;
        }
        for ( ${name} val : values() )
        {
            if ( rep.equals( val.toString() ) )
            {
                return val;
            }
        }
        return valueOf( rep );
    }
}

--
Lew

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