[FIXED] How to print math multiplication table returning String value in 2x2 and 3x3 matrix using nested loops in Java

Issue

I'm trying to get the method that would return the following String for an integer parameter of 2:

Output:

Same for parameter of 3

The code which I got so far is below:

public String simpleMultiplicationTable(int num) {
    for(int i = 1 ;i<=num;i++) {
        for(int j=1;j<=num;j++) {
            System.out.format("%4d",i*j);
        }
        System.out.println();
    }
    return String.valueOf(num);      
}

Solution

Instead of printing each value, append it to a StringBuilder and return the same at the end.

Do it as follows:

public class Main {
    public static void main(String[] args) {
        // Tests
        System.out.println(simpleMultiplicationTable(2));
        System.out.println(simpleMultiplicationTable(3));
    }

    public static String simpleMultiplicationTable(int num) {
        StringBuilder sb = new StringBuilder();
        for (int i = 1; i <= num; i++) {
            for (int j = 1; j <= num; j++) {
                sb.append(i * j);
                if (j < num) {
                    sb.append(" ");
                }
            }
            if (i < num) {
                sb.append("\n");
            }
        }
        return sb.toString();
    }
}

Output:

1 2
2 4
1 2 3
2 4 6
3 6 9

Using String instead of StringBuilder:

public class Main {
    public static void main(String[] args) {
        // Tests
        System.out.println(simpleMultiplicationTable(2));
        System.out.println(simpleMultiplicationTable(3));
    }

    public static String simpleMultiplicationTable(int num) {
        String table = "";
        for (int i = 1; i <= num; i++) {
            for (int j = 1; j <= num; j++) {
                table += j < num ? i * j + " " : i * j;
            }
            if (i < num) {
                table = table + "\n";
            }
        }
        return table;
    }
}

JUnit Tests

import static org.junit.Assert.assertEquals;
import static org.junit.Assert.fail;

import org.junit.jupiter.api.Test;

class TestMethods {

    @Test
    public void testSimpleMultiplicationTable() {
        Table table = new Table();
        String result = table.simpleMultiplicationTable(2);
        if (result.contains(" \n")) {
            fail("Your output table has one or more extra spaces before the newline character. You can use the trim() function to remove additional spaces");
        }
        assertEquals("1 2\n2 4", result);

        result = table.simpleMultiplicationTable(1);
        if (result.contains(" \n")) {
            fail("Your output table has one or more extra spaces before the newline character. You can use the trim() function to remove additional spaces");
        }
        assertEquals("1", result);
    }
}

class Table {

    public String simpleMultiplicationTable(int num) {
        String table = "";
        for (int i = 1; i <= num; i++) {
            for (int j = 1; j <= num; j++) {
                table += j < num ? i * j + " " : i * j;
            }
            if (i < num) {
                table = table + "\n";
            }
        }
        return table;
    }
}

Answered By - Arvind Kumar Avinash