Having trouble with return variable scope in java

Question

I want to return a String/StringBuilder of a large letter E that is filled in with E's such that I get something like this:

EEEEEE
E
E
E
EEEEEE
E
E
E
EEEEEE

The issue I am having right now is that I have a StringBuilder value, sb, that should be getting updated during the nested for loop. What do I have to do to have my function drawLetters return sb so that I can print it in my main() function?

The error I get is drawLetters is missing a return statement. I tried to move the sb outside of the for loop, but then the for loop doesn't update the variable because it is outside of the for loop scope.

tl;dr - confused about scope and where the sb variable should go so that my function drawLettersreturns sb

public class MCVE {

    public static String drawLetters(String string) {
        // Create BufferedImage object called "background".
        BufferedImage background = new BufferedImage(144, 32, BufferedImage.TYPE_INT_RGB);

        // Creates a Graphics2D object called "g" by calling the method get.Graphics() on the background
        Graphics g = background.getGraphics();

        // This decides what is drawn.
        g.drawString(string, 6, 12);

        StringBuilder sb = new StringBuilder();
        for (int y = 0; y < 32; y++) {
            for (int x = 0; x < 144; x++)
                sb.append(background.getRGB(x, y) == -16777216 ? " " : background.getRGB(x, y) == -1 ? string : "*");
            if (sb.toString().trim().isEmpty())
                continue;
        }
        return sb.toString();
    }


    public static void main(String[] args) {
        System.out.println(drawLetters("E"));
        //drawLetters("J");
        //drawLetters("K");
    }
}

Declare sb outside of the loop if you plan to return it outside of the loop — GBlodgett
– GBlodgett, Commented Jan 22, 2019 at 18:33
You forgot block braces for your for-loop. The if-statement seems to be intended to be inside the loop. — RaminS
– RaminS, Commented Jan 22, 2019 at 18:34
If sb.toString().trim().isEmpty() is always true, the return will never be reached. I'm not sure what the potential for that happening is. — Carcigenicate
– Carcigenicate, Commented Jan 22, 2019 at 18:34
And change method to return String and do return sb.toString();, it makes more sense to return the actual value — Joakim Danielson
– Joakim Danielson, Commented Jan 22, 2019 at 18:34
The compiler complains of a missing return statement because of cases where your return might never be reached, in the view of the compiler. — Andy Thomas
– Andy Thomas, Commented Jan 22, 2019 at 18:36

GBlodgett · Accepted Answer · 2019-01-22 18:35:04Z

2

You declare sb inside the loop:

for (int y = 0; y < 32; y++) {
    StringBuilder sb = new StringBuilder();
    //...
} //Scope of sb ends here

So it is out of scope outisde of the outer for loop. Right now you are trying to return it inside the for loop, which works, but isn't what you want. Declare it outside of the loop:

StringBuilder sb = new StringBuilder();
for (int y = 0; y < 32; y++) {        
    for (int x = 0; x < 144; x++)
        sb.append(background.getRGB(x, y) == -16777216 ? " " : background.getRGB(x, y) == -1 ? string : "*");
    if (sb.toString().trim().isEmpty()) 
        continue;        
}
return sb;

Also if you want to print sb, use the toString() method, and do it before you return; otherwise it is an unreachable statement.

If I were you, I would return a String, and not a StringBuilder. Otherwise everytime you call the method and try to print it you will have to add in a toString() call. You can change your method signature to:

public static String drawLetters(String string)

And then in your return statement

return sb.toString();

answered Jan 22, 2019 at 18:35

GBlodgett

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2 Comments

Evan Kim Over a year ago

I made the changes, but did I do something wrong still? Nothing is printing out

GBlodgett Over a year ago

@EvanKim Your code has the possibility to return an empty String. I would debug to see what it is returning

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