Java Program:

Example:

A
A B
A B C

import java.util.Scanner;

public class Pattern {

  public static void main(String[] args) {
    Scanner userInput = new Scanner(System.in);
    System.out.print("Enter number of rows : ");

    int rows;
    char c;
    rows=userInput.nextInt();
    for(int i=1; i<=rows; i++) {
      c='A';
      for(int j=1; j<=i; j++) {
        System.out.print((c++) +" ");
      }
      System.out.print("\n");
    }

  }
}

Output:

  Enter number of rows : 4
  A
  A B
  A B C
  A B C D

Main logic :

for(int i=1; i<=rows; i++) {  //rows : number of rows to print
  c='A';
  for(int j=1; j<=i; j++) {
    System.out.print((c++) +" ");
  }
  System.out.print("\n");
}

You can print the same pattern in small alphabets, just set c='a'