Assign variable value of an other variable dynamically in Java

Question

lets pretend I have the following:

public class Something{

    private final String VALUE_AAA = "ABC";
    private final String VALUE_BBB = "DEF";
    private final String VALUE_CCC = "GHI";

    public String getValue(String param) {

    }
}

Now I want if I pass the value BBB to getValue in return DEF

Is that possible? I don't want if - else statements. I tought about BeanUtils but I am not sure.

Thanks, Hauke

no that is not an option. I made this example easier with numbers, but in my project I need to put a string at the end of value_ instead of a number. For example VALUE_AAA, VALUE_BBB, VALUE_CCC and I pass to the method BBB. — Hauke
– Hauke, Commented Aug 27, 2011 at 7:09
You could then use a HashMap. The only language (that I know of) where you can do this in a (relatively) straightforward fashion is PHP. — NullUserException
– NullUserException, Commented Aug 27, 2011 at 7:12
Okay I thought about that also, but I hoped that something like this would work "String x = VALUE_+param;" Within script languages that works. I think I will do it with the map solution. Thanks :-) — Hauke
– Hauke, Commented Aug 27, 2011 at 7:15
If you're OK with reflection you can use it to achieve exactly what you need. See below. — Itay Maman
– Itay Maman, Commented Aug 27, 2011 at 7:35

Rajeev Sreedharan · Accepted Answer · 2011-08-27 09:00:50Z

3

Maybe you could use a HashMap,

public class Something{

    protected final HashMap<Integer, String>() hashMap = new HashMap<Integer, String>(){{
        put(new Integer(1),"ABC");
        put(new Integer(2),"DEF");
        put(new Integer(3),"GHI");
    }}

    public String getValue(Integer nr) {
        return hashMap.get(nr);
    }
}

EDIT

It seems these set of values are preintialized in class itself, For String parameter as input you could use:

public class Something{

protected final HashMap<String, String> hashMap = new HashMap<String, String>(){{
    put("AAA","ABC");
    put("BBB","DEF");
    put("CCC","GHI");
}};

public String getValue(String nr) {
    return hashMap.get(nr);
}

}

I've skipped the "Value_" since if you decide to use the HashMap, you wouldn't need a variable name as such, just the key.

edited Aug 27, 2011 at 9:00

answered Aug 27, 2011 at 7:16

Rajeev Sreedharan

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3 Comments

user unknown Over a year ago

a) pass a String ("BBB"), b) missing keyword 'return'. c) in () hashMap the parens are wrong. If you remove them, it still doesn't compile.

Rajeev Sreedharan Over a year ago

@user unknown: If you did note, the question is a edited revision with a String parameter as input from an Integer asked by the OP.

user unknown Over a year ago

No, I didn't mention. The rules of SE discourage to change the meaning of an edit, so I don't inspect the history of a question, before answering and reacting. However, rerurning return new String [] {"AAA", "BBB", "CCC"}[param-1]; would then have been sufficient, and, btw., your Code doesn't compile.

Itay Maman · Accepted Answer · 2011-08-27 08:43:19Z

0

You can use reflection: Get the current object's class, lookup the field by its name, then extract this field's value at the current object:

public class Something {

  private final String VALUE_AAA = "ABC";
  private final String VALUE_BBB = "DEF";
  private final String VALUE_CCC = "GHI";

  public String getValue(String param) throws Exception {
     return (String) this.getClass().getDeclaredField("VALUE_" + param).get(this);
  }
}

More details: http://download.oracle.com/javase/1,5.0/docs/api/java/lang/Class.html#getDeclaredField(java.lang.String)

edited Aug 27, 2011 at 8:43

answered Aug 27, 2011 at 7:24

Itay Maman

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3 Comments

rompetroll Over a year ago

you probably need getDeclaredField() because the fields are private.

user unknown Over a year ago

unreported exception java.lang.NoSuchFieldException; must be caught or declared to be thrown

Itay Maman Over a year ago

Thanks @deadsven and userunknown. Fixed.

user unknown · Accepted Answer · 2011-08-27 09:49:15Z

0

Sorry, working code:

public class HundM
{
    protected final static HashMap <String, String> hm = new HashMap <String, String> (); 

    public static String getValue (String param) {
        return hm.get (param);
    }

    public static void main (String args[])
    {
        hm.put ("AAA", "ABC");
        hm.put ("BBB", "DEF");
        hm.put ("CCC", "GHI");
        System.out.println (getValue ("BBB"));
    }
}

edited Aug 27, 2011 at 9:49

answered Aug 27, 2011 at 8:10

user unknown

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2 Comments

Rajeev Sreedharan Over a year ago

Observe the question he isn't expecting the values to be dynamically put but rather as a literal, plus whats the point of adding the "Value_" if you are using HashMap. But otherwise your code would 've been just fine.

user unknown Over a year ago

Yes, "VALUE_" was somehow a stupid idea. Thank you. What do you mean "dynamically put"? That's just not the scope of the question. A datastructure (HashMap) and a form to get the values in and out. Whether he wants to add more values to the hashmap later or not isn't part of the question, as I understood it.

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