如何使用数组元素声明变量？

Question

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[] (ie 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.

Answer 1

You initialized your array as:

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

ie an array of String s.

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.

Answer 2

Two things;

Firstly you've declared your array as and array of String s 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];

Answer 3

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") .

Answer 4

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

Answer 5

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);
   }
}