How can I convert a 2d Number array into a 2d String array?

Question

I'm really new to java or programming, so i have a "basic" quesion (I guess). I have this code, which generates me an array of numbers. I want to convert that into an array of strings. Can someone please fix my code?

public class HelloWorld{
    public static void main(String[] args) {
        Number[][] values = new Number[10][12];
        for (int i = 0; i < values.length; i++) {
            for (int j = 0; j < values[i].length; j++) {
                values[i][j] = Math.floor(Math.random() * 100000) / 100000;

                System.out.print(values[i][j] + " ; ");
            }
            System.out.println();
        }
    }
}

Do you still need the array of Numbers afterwards? If not, just convert the number to a string as soon as you generate it an declare values as String[][]. As an aside, why use Number when double is more than adequate? — Federico klez Culloca
– Federico klez Culloca, Commented Oct 14, 2020 at 12:10
Yes, I need the numbers afterwards. And with the doubles / numbers array, thank you for that hint — Klippspringer
– Klippspringer, Commented Oct 14, 2020 at 12:14

WatermelonOof · Accepted Answer · 2020-10-14 12:17:39Z

2

You can simply use String array instead of Number array. When setting the element, use String.valueOf(YOUR_NUMBER)

answered Oct 14, 2020 at 12:17

WatermelonOof

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2 Comments

Klippspringer Over a year ago

So I write String [][] values = new String[12][10]; and than? Where do I use your String.valueOf?

WatermelonOof Over a year ago

In here just add: `values[i][j] = String.valueOf(Math.floor(Math.random() * 100000) / 100000);

Alexandra Dudkina · Accepted Answer · 2020-10-14 12:23:29Z

1

The most obvious way:

public static String[][] convert(Number[][] numbers) {
        String[][] result = new String[numbers.length][];
        for (int i = 0; i < numbers.length; i ++) {
            Number[] row = numbers[i];
            result[i] = new String[row.length];
            for(int j = 0; j < row.length; j ++) {
                result[i][j] = row[j] == null ? null : row[j].toString();
            }
        }
        return result;
    }

Less obvious way:

public static String[][] convert(Number[][] numbers) {
        return Arrays.stream(numbers)
                .map(row -> Arrays.stream(row).map(n -> String.valueOf(n)).toArray(String[]::new))
                .toArray(String[][]::new);
    }

answered Oct 14, 2020 at 12:23

Alexandra Dudkina

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6 Comments

Klippspringer Over a year ago

Thank you, but how do I add this to my class? Just as a second method or do I have to change something?

Alexandra Dudkina Over a year ago

Yes, add method to your class and call it like String [][] strValues = convert(values);

Klippspringer Over a year ago

Do I have to rename it? Cause when I copy & paste it and than change the line to "String [][] strValues = convert(values);", I get some error messages. I'm really new to java so sorry for that stupid quesions.

Alexandra Dudkina Over a year ago

No need to rename, it should be enough to place method inside your class and make sure it's static when calling it from main().

Klippspringer Over a year ago

Okay thank you, but one last question: how are these two methods connected?

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