Re: Variable in Setter

From:

"Mike Schilling" <mscottschilling@hotmail.com>

Newsgroups:

comp.lang.java.programmer

Date:

Fri, 10 Aug 2007 23:03:11 -0700

Message-ID:

<Aicvi.164$vw7.1@nlpi070.nbdc.sbc.com>

Joshua Cranmer wrote:

teser3@hotmail.com wrote:

I have this:
BeanChalker.setLastname(lastname);

Is it possible to use variables like this because I am not sure how
to set up the variable or use concatenator some way to make it work:

String myvariableOne = "Lastname";
String myvariableTwo = "lastname";
BeanChalker.set + myvariableOne + (myvariableTwo);

If I understand you correctly, what you want is a runtime method
dispatch. The short answer to your question is "no it is not
possible." The medium answer is "well, yes it is, but it is generally
not a good idea to try and use."

The easiest way to do what you want to do is to manually set functions
up yourself:

class Foo {
   private String varA, varB, varC;
   // constructors, etc.

   public void setA(String newA) {varA = newA;}
   public void setB(String newB) {varB = newB;}
   public void setC(String newC) {varC = newC;}

   public void set(String variable, String value) {
       if ("A".equals(variable))
           setA(value);
       else if ("B".equals(variable))
           setB(value);
       else if ("C".equals(variable))
           setC(value);
       else
           throw new IllegalArgumentException("Variable "+variable+
               " not found!");
   }
}

If you really want the long answer, you probably don't. Use the
previous solution if at all feasible or not at all.

Still want it? Here's the reflection method:

class Foo { /* Defined similar to above sample, except w/o set */ }

class Test {
    public void foobar() {
        String variable = "Lastname";
        String value = "Stroustrup"; // Kudos if you get the
        reference! Foo bar = new Foo(); // assume it works

        Class<?> fooClass = Foo.class;
        try {
           Method m = fooClass.getMethod("set"+variable);
           m.invoke(bar,value);
        } catch (Exception e) { // See the APIs for all exceptions
            // Don't do this in real code.
        }
    }
}

I don't recommend that approach.

A very nice and thorough answer. I have one more suggestion. If what
you're really looking for is a way to choose a setter, and only a setter
(OK, maybe a getter too), at runtime, you're better off having a single set
method that accesses a map:

    private Map values = new HashMap();

    public void set(String key, String value)
    {
        values.set(key, value);
     }

    public String get(String key)
    {
        return values.get(key);
    }

or, if you want to constrain the set of possible keys, add the following

    static Set keys;
    static
    {
        keys = new HashSet()
        keys.add("firstName");
        keys.add("lastName");
        //etc.
    }

    private checkKey(String key)
    {
        if (!keys.contains(key))
            throw new IllegalArgumentException(key);
    }

and begin both get() and set() with calls to checkKey().