Pascal's Triangle

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class PascalTriangle {
  private static final String NEW_LINE = System.getProperty("line.separator");

  private long[][] triangle;

  public PascalTriangle(int rowCount) {
    if (rowCount <= 0) {
      return;
    }
    triangle = new long[rowCount][];
    for (int r = 0; r < rowCount; r++) {
      int colCount = r + 1;
      triangle[r] = new long[colCount];
      triangle[r][0] = 1;
      triangle[r][colCount - 1] = 1;
      for (int c = 1; c < colCount - 1; c++) {
        triangle[r][c] = triangle[r - 1][c - 1] + triangle[r - 1][c];
      }
    }
  }

  public long getValue(int row, int col) throws IllegalArgumentException {
    if (triangle == null) {
      return 0;
    }
    if (col > row) {
      throw new IllegalArgumentException(
          "Invalid column entry, column value cannot be greater than row value");
    }
    return triangle[row - 1][col - 1];
  }

  public String getTriangleDisplay() {
    if (triangle == null) {
      return null;
    }
    StringBuilder triangleBuilder = new StringBuilder();
    for (int r = 0; r < triangle.length; r++) {
      triangleBuilder.append(r != 0 ? NEW_LINE : "");
      for (int c = 0; c < triangle[r].length; c++) {
        triangleBuilder.append(c != 0 ? '\t' : "");
        triangleBuilder.append(triangle[r][c]);
      }
    }
    return triangleBuilder.toString();
  }

  public static void main(String[] args) throws Exception {
    BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
    int row = 0;
    int col = 0;

    String line;
    while ((line = prompt(in)) != null) {
      if (line.startsWith("exit")) {
        break;
      }
      String[] input = line.split(",\\s+");
      try {
        row = Integer.parseInt(input[0]);
        if (row <= 0) {
          throw new IllegalArgumentException();
        }
      } catch (IllegalArgumentException e) {
        System.err
            .println("Invalid row entry, expected positive integer but got "
                + input[0]);
        continue;
      }
      try {
        col = Integer.parseInt(input[1]);
        if (col <= 0) {
          throw new IllegalArgumentException();
        }
      } catch (IllegalArgumentException e) {
        System.err
            .println("Invalid column entry, expected positive integer but got "
                + input[1]);
        continue;
      }

      PascalTriangle triangle = new PascalTriangle(row);
      long value = 0;
      try {
        value = triangle.getValue(row, col);
      } catch (IllegalArgumentException e) {
        System.err.println(e.getMessage());
        continue;
      }

      System.out.println("Output: " + value);
      System.out.println();
      System.out.println(triangle.getTriangleDisplay());
      System.out.println();
    }
  }

  private static String prompt(BufferedReader in) throws IOException {
    System.out.println();
    System.out.print("Enter Input (type 'exit' to end): ");
    return in.readLine();
  }
}