Referring a variable with a variable in java

Question

I have got into a strange strange situation. I have 3 sets of strings like this

String set1q1="something";    //associated with randomNum=1
String set1q2="something";
String set1q3="something";
String set1q4="something";
... and so on

String set2q1="something";    //randomNum=2
String set2q2="something";
String set2q3="something";
String set2q4="something";
... and so on

String set3q1="something";    //randomNum=3
String set3q2="something";
String set3q3="something";
String set3q4="something";
... and so on

All these strings are initialised only once. Now in my program i generate a random number between 1-3. I converted this random number into a string and stored it into a string called set.

String set=randomNum.toString();

Now next intead of using "if-else" to send the data(if randomnum=1 send set1q1-5, if randomnum=2 then send set2q1-5), I want the appropriate data to be sent using one line.

For example: if random no 2 is chosen then set2q1 has to be sent where the "2" in between is has to be the value of "set"(which is defined above).

set"set"q1    //where set can be 1,2,3

Is there any way to do this?

Why not use an array to hold each "set" and simply use the index? — Brian Roach
– Brian Roach, Commented Mar 7, 2012 at 9:15
@deporter: I will try lists. It seems to be a good Idea. Will HashMap also be appropriate? — Ashwin
– Ashwin, Commented Mar 7, 2012 at 9:23
@user1139023 how will you populate the hashmap? manually? it is not a good practice for your problem, use list. — Juvanis
– Juvanis, Commented Mar 7, 2012 at 9:55

Oliver Charlesworth · Accepted Answer · 2012-03-07 09:22:14Z

6

What you are asking for is not possible;¹ it's just not the way Java works. Why don't you just use an array, or a collection?

List<List<String>> allTheStrings = new ArrayList<List<String>>();

List<String> myStrings = null;

// Add a subset
myStrings = new ArrayList<String>();
myStrings.add("something");
myStrings.add("something");
myStrings.add("something");
allTheStrings.add(myStrings);

// Add another subset
myStrings = new ArrayList<String>();
myStrings.add("something");
myStrings.add("something");
myStrings.add("something");
allTheStrings.add(myStrings);


...

// Obtain one of the strings
String str = allTheStrings.get(1).get(2);

_{1. Except in the case where these variables are members of a class, in which case you could use reflection. But really, don't.}

edited Mar 7, 2012 at 9:22

answered Mar 7, 2012 at 9:14

Oliver Charlesworth

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8 Comments

Juvanis Over a year ago

but did you get the question, he doesn't mention about his desire to use arrays or lists.he is asking a "varying portion" in the name of a variable. ok?

Oliver Charlesworth Over a year ago

@deporter: I indeed got the question. But this is the correct answer; the OP needs to be informed that what he/she wants is not how Java works.

Deco Over a year ago

+1: This is what should be done, a data structure. Although the OP asked about pseudo-reflection, as @OliCharlesworth mentioned - dont. A HashMap could also work here too to meet the OPs requirements.

Ashwin Over a year ago

@Deco: Even I was thinking of HashMaps. Seems to be a good Idea. thank you . I will try that also.

Oliver Charlesworth Over a year ago

@user1139023: There's little value in a HashMap here. HashMaps are useful when your indexes are non-contiguous, or are a complex data-type.

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bisgardo · Accepted Answer · 2012-03-07 09:16:29Z

1

It is not possible. Local variable identifiers are converted to numbers (stack offsets) during compilation. But you should use arrays or collections anyway

answered Mar 7, 2012 at 9:16

bisgardo

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Comments

Synesso · Accepted Answer · 2012-03-07 09:22:16Z

1

Sounds like you want to index Strings by two indices. You should use a two-dimensional String array: String[][] strings. You may then access the desired string with strings[n][m]

Or you can achieve the same effect with a List<List<String>> strings if you need the dimensions of your 2D array to grow dynamically. You'd access the value you need with strings.get(n).get(m)

If you really want to access your strings by a composed name such as set2q1, then you just need a Map<String, String> strings. Then you'd access each value with strings.get("set" + m + "q" + n)

answered Mar 7, 2012 at 9:22

Synesso

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2 Comments

Ashwin Over a year ago

Does using Map have any side affects - like consumer memory or something like that. Basically I am asking was hash map meant for this - accessing your object using a string to refer to it.

Synesso Over a year ago

The overhead is minimal. The collection classes all have their distinct qualities and capabilities. You can use a Map anytime you wish to create a set of references from one domain to another. For example Map<Person, Address> workplaceAddresses or Map<Integer, Element> periodicTableOfElements etc.

Tom · Accepted Answer · 2012-03-07 09:15:02Z

0

looks to me you should look into arrays, like this:

String[] strings = new String[]{"xxx", "yyy", "zzz"};
String string = strings[randomNumber];

answered Mar 7, 2012 at 9:15

Tom

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Comments

NimChimpsky · Accepted Answer · 2012-03-07 09:15:03Z

0

create an arraylist instead and reference using the list index

answered Mar 7, 2012 at 9:15

NimChimpsky

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1 Comment

Juvanis Over a year ago

he is asking a varying portion in the name of a variable. of course arrays should be preferred. but the question is different. i will downvote it, please remove.

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