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I have an array of elements and I want to use the elements in the array as variables.

I want to do this because I have an equation, the equation requires multiple variable inputs, and I want to initialize an array, iterate through it, and request input for each variable (or each element of the array).

So I have an array like this: 

String variableArray[] = {"a", "b", "c"}

And now I'm iterating through this array and getting the input from the user:

for(int i=0; i<3; i++) {
    System.out.printf("Enter value for %s: ", variableArray[i]);
    int variableArray[i] = keysIn.nextInt();
}

The problem is this line doesn't compile:

int variableArray[i] = keysIn.nextInt();

In essence, I want to use the elements of the array variableArray[] (i.e. a, b, and c) as variables so I don't have to do the same process for each variable. I can't imagine how it's done when there are many variables to input (I wouldn't want to type that all out).

tl;dr I want to streamline the process of inputting values for multiple variables.

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  • 1
    Remove the int from the declaration of the "variable": variableArray[i] = keysIn.nextInt(); Commented Sep 25, 2012 at 23:39
  • This doesn't work because you're inputting an int into the string variableArray (which is totally aside from what I want to do anyways). Commented Oct 2, 2012 at 22:46

5 Answers 5

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You initialized your array as:

String variableArray[] = {"a", "b", "c"}

i.e. an array of Strings.

If you want to refer later to the i-th element, you just write:

variableArray[i]

without any int before - you can't initialize single entries in a array.

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Java doesn't work like that. "a" is a string literal, and you can't use it as if it were a variable. There's no magical way to go from having an array element whose value is "a" to having an int variable called a.

There are, however, some things you can do that are probably equivalent to what you want.

String variableArray[] = {"a", "b", "c"}
int valueArray[] = new int[variableArray.length];

for(int i=0; i<3; i++) {
    System.out.printf("Enter value for %s: ", variableArray[i]);
    valueArray[i] = keysIn.nextInt();
}

To get the value of "a", do valueArray[0].

Here's another more sophisticated suggestion:

String variableArray[] = {"a", "b", "c"}
HashMap<String, Integer> variableValues = new HashMap<String, Integer>();

for(int i=0; i<3; i++) {
    System.out.printf("Enter value for %s: ", variableArray[i]);
    variableValues.put(variableArray[i],  keysIn.nextInt());
}

To get the value of "a", do variableValues.get("a").

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2 Comments

I've realized I'm trying to make Java do something it can't. What you suggested is not what I'm looking for because I still have to initialize the variables, i.e. a = variableValues.get("a"), b = variableValues.get("b"), and so on.
No, my suggestion is that you do away with your variables altogether and just use variableValues.get instead, when you write up your equation. And if you've already written your equation, well, re-writing it is still probably less work that initializing all your variables. :)
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Two things;

Firstly you've declared your array as and array of Strings so variableArray[i] = keysIn.nextInt() won't work any way, int can't be stored in a String array.

Secondly, int variableArray[i] = keysIn.nextInt(); is incorrect, because variableArray has already been declared (as a String array and variableArray[i] is a String element of that array)

The line should read variableArray[i] = keysIn.next();, but this will store the text the user has entered, not a numerical value.

What it could look like is...

String labelArray[] = {"a", "b", "c"}
int variableArray[] = new int[3];
// You could declare this as
// int variableArray[] = {0, 0, 0};
// if you wanted the array to be initialized with some values first.
for(int i=0; i<3; i++) {
    System.out.printf("Enter value for %s: ", labelArray[i]);
    variableArray[i] = keysIn.nextInt();
}

UPDATED

int a = variableArray[0];
int b = variableArray[1];
int c = variableArray[2];
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4 Comments

This works but it's not what I am looking for functionally. Later in the program, I want to be able to call on the variables by their name, and I can't do that with an array, i.e. d = a + c + b, as opposed to d = variableArray[0] + variableArray[1] + variableArray[2].
What variables? variableArray as an array of variables (or a list of)...?
If I use the code you've provided me, I wouldn't be able to say right after int d = a + b + c; because a, b, and c are variables that haven't been initialized. They're in an array. Does this make sense?
I'm sorry MadProgrammer. Of course you can do that, I knew that. But I didn't want so many lines of code to represent such a simple process. I guess I'm going to have to make do with this though.
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Please use with caution, but after reading your comments to the other answers, you might get a little closer to the way you want it using reflection:

import java.lang.reflect.Field;
import java.util.Scanner;

public class VariableInput {
   public static class Input {
     public int a;
     public int b;
     public int c;
   }

   public static void main(String[] args) throws IllegalArgumentException,
       IllegalAccessException {
      Scanner keysIn = new Scanner(System.in);
      Field[] fields = Input.class.getDeclaredFields();
      Input in = new Input();
      for (int i = 0; i < 3; i++) {
         System.out.printf("Enter value for %s: ", fields[i].getName());
         fields[i].set(in, keysIn.nextInt());
      }
      int d = in.a + in.b + in.c;
      System.out.println("d=" + d);
   }
}
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2 Comments

This is beautiful code! I'm working my way through this and I'm understanding more and more of it. What does this do: Input in = new Input();? I can see in is the first argument in fields[i].set and also it is what is used to call a value to the variables, as in in.a or in.b. But what does it do?
@45lbplates The line Input in = new Input(); creates an instance of the class Input. This instance gets the name 'in' and is then used to store the values for a, b, and c. Those can be accessed via in.a, in.b etc. It doesn't do anything else.
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What you are actually looking for is a Map. It's a collection of mappings from one value to another value. In your case, you can use it to assign an integer value (the value of a variable) to a string that represents the name of a variable.

Therefore you would create an instance of a Map<String, Integer> - read "a map from String to Integer".

See this tutorial for details on the subject.

Now what would your code look like with it:

String[] variableNames = { "a", "b", "c" };
// create the map object
Map<String, Integer> variableValues = new LinkedHashMap<String, Integer>();

// read variable values and put the mappings into the map
for (int i = 0; i < variableNames.length; i++) {
    System.out.printf("Enter value for %s: ", variableNames[i]);
    variableValues.put(variableNames[i], keysIn.nextInt());
}

// print value of each variable
for (int i = 0; i < variableNames.length; i++) {
    String varName = variableNames[i];
    System.out.println(varName + " = " + variableValues.get(varName));
}

Output:

Enter value for a: 5
Enter value for b: 4
Enter value for c: 8

a = 5
b = 4
c = 8
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1 Comment

João Mendes suggested the same process. I explained to him that this is not what I am looking for because I still have to initialize the variables (look at the comment I made on his answer). I've reached the limits of Java.

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