How do I convert triangle pattern to letter?

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Java

netbeans

I need to do a triangle with letter X with the number of length the user input. i did the triangle with the numbers.Example:
1
12
123
but i need to do with letter X, example:
X
XX
XXX

What I have tried:

int triangle = 3;
          System.out.println("You have entered '2' for 'Triangle'.");

          System.out.println("Please enter the length of the side:");

          int length =kb.nextInt();
          for(int row=1;row<=length;row++){

          }