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Use a variable within a variable? Java

Hi this is a general programming related question more so than a java question. If i have a program like this : 

public class tester {

    public static void main(String[] args) {
        int i = 2;
        String text = "Hello";
        String text2  = "world";

        System.out.println(text);
        System.out.println(text + i);
    }    
}

I want to print "hello", then "world" but instead i print "hello" and then "hello2". is there anyway i can access the variable text2 by appending the counter i to the variable test? I need a solution for this for a much more complicated program i am working on

Thanks, Matt

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  • Do you need to loop over a list of variables and print them all out? Easy solution would be to use a List and iterate over that rather than use individual variables. Commented Aug 10, 2011 at 10:04
  • You can't do it without using arrays. Commented Aug 10, 2011 at 10:38

5 Answers 5

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2

You can do this using an array:

String[] text = new String[2];
text[0] = "Hello";
text[1] = "world";

System.out.println(text[0]);
System.out.println(text[1]);

You can also index the array using a variable:

int i = 1;
System.out.println(text[i]);

Java does not generally support constructing (local) variable names at runtime. This is true of most (but not all) programming languages.

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2

You can't generally do this in Java - certainly not for local variables. Normally if you want to map a string or integer to a value, you should use a Map<String, ...>, a Map<Integer, ...> or an array instead of separate variables.

For instance or static variables you could use reflection to achieve this, but I would strongly advise you not to. Basically you should treat variables as separate storage locations which happen to have names at compile time, not a mapping from names to values. If you need the latter, create that mapping explicitly.

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2

Maybe you want to look at arrays:

String[] texts = { "Hello", "world"};

for (int i=0; i<2; i++)
    System.out.println(texts[i]);

for (String text : texts)
   System.out.println(text);
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It is because Java evaluates the expression inside System.out.println(expr) first, then convert it to a String. When Java evaluates the expression, it follows the left-to-right rule.
So, you get 

System.out.print("hello"+2); // hello2
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You cannot access local variable by name, however you can access fields by name.

public class Tester {
    public static final String text = "Hello";
    public static final String text2  = "world";

    public static void main(String[] args) {
        int i = 2;
        System.out.println(Tester.class.getField("text").get(null));
        System.out.println(Tester.class.getField("text"+i).get(null));
    }
}

This practice is discouraged for obvious reasons.

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