Java中的乘法表使用方法

Question

Write a method that returns a multiplication table based on two input values that specify what two ranges of numbers to multiply together. For example, if the method were given 3 and 4 as input, it would return a string that when printed, would look like this:

1 2 3 4

2 4 6 8

3 6 9 12

Output Requirements:

Each number must be followed by a tab character. Each line must be followed by a new line character (including the last row). The columns and rows should range from 1 to the input number. The method signature should look as follows:

public static String multiplicationTable(int rows, int columns){}

Call the testMT() method from main after completing this method to ensure it is working as expected.

public static String multiplicationTable(int rows, int columns) {

        for(int i = 1; i <= rows; i++){
            for(int j = 1; j <= columns; j++) {
                int num = i * j;
                String a = "" + num +"\t";
            }
            System.out.println("");
        }
        return String.format("%s", a); 
    }
public static void testMT() {
     System.out.println("Testing Multiplication Table");

     String expected = "1\t2\t3\t4\t\n2\t4\t6\t8\t\n3\t6\t9\t12\t\n";
     System.out.print("Expecting:\n" + expected);

     String actual = multiplicationTable(3, 4);
     System.out.print("Actual:\n" + actual);

     boolean correct = expected.equals(actual);
     System.out.println("Outputs equal? " + correct);
     }

Here is my output:

Testing Multiplication Table Expecting:

1 2 3 4
2 4 6 8
3 6 9 12

Actual:

12 Outputs equal? false

I feel like I have the right setup but I can't figure out how to get the expected output.

Answer 1

Your multiplicationTable method is printing, and not quite legal. Build the table and return it. Something like,

public static String multiplicationTable(int rows, int columns) {
    StringBuilder sb = new StringBuilder();
    for (int i = 1; i <= rows; i++) {
        for (int j = 1; j <= columns; j++) {
            int num = i * j;
            sb.append(num).append('\t');
        }
        sb.append('\n');
    }
    return sb.toString();
}

With no other changes, I then get

Testing Multiplication Table
Expecting:
1   2   3   4   
2   4   6   8   
3   6   9   12  
Actual:
1   2   3   4   
2   4   6   8   
3   6   9   12  
Outputs equal? true