Even with the correct code, students often hit frustrating roadblocks. Here’s a quick troubleshooting table:
| Error Message / Symptom | Likely Cause | Solution | |-------------------------|--------------|----------| | Square is not filled | Missing setFilled(true) | Add the line before setting the color. | | All squares are the same color | Incorrect modulus logic | Use (row + col) % 2 == 0 . Check your starting color. | | ArrayIndexOutOfBoundsException | Using <= instead of < in loop | Ensure loops run 0 to 7 (not 0 to 8 ). | | Nothing appears on screen | Forgot to call add(square) | After creating and coloring, call add(square) . | | Squares overlap or have gaps | Incorrect coordinate math | x = col * size , y = row * size . Don’t add extra offset. | | Autograder fails on style | Missing constants or comments | Use private static final int for magic numbers (8, 50). | Simply copying the code might get you a checkmark, but CodeHS often includes a quiz or subsequent exercise that requires you to modify the pattern. Here’s how to adapt your solution for different scenarios: 1. Changing the Board Size If you need a 10x10 board, change NUM_ROWS and NUM_COLS to 10. Adjust SQUARE_SIZE to getWidth()/10 . 2. Changing the Colors Swap out Color.RED and Color.BLACK for any valid java.awt.Color (e.g., Color.BLUE , Color.YELLOW , Color.MAGENTA ). 3. Adding a Border To make each square stand out, add: 9.1.7 checkerboard v2 answers
private static final int NUM_ROWS = 8; private static final int NUM_COLS = 8; private static final int SQUARE_SIZE = 50; // Pixels per square Even with the correct code, students often hit
A: No. Some versions of 9.1.7 use black and gray. If the sample image shows gray, replace Color.RED with Color.GRAY . Check your starting color
import acm.graphics.*; import acm.program.*; import java.awt.*; public class Checkerboard extends GraphicsProgram
If you've landed on this article, you're likely working through the CodeHS Java course (specifically the "Methods and Control Structures" or "Basic Java" units) and have hit the infamous 9.1.7 Checkerboard v2 exercise. Don't worry—you're not alone. This problem is a rite of passage for learning nested loops, modulus logic, and graphical user interface (GUI) manipulation in Java.
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