minor changes based on narrative

ChrisMayfield · ChrisMayfield · commit c32030b7887a · 2019-09-18T01:27:43.000-04:00
diff --git a/ch15/Cell.java b/ch15/Cell.java
@@ -34,7 +34,7 @@ public Cell(int x, int y, int size) {
      * @param g graphics context
      */
     public void draw(Graphics g) {
-        g.setColor(color);
+        g.setColor(this.color);
         g.fillRect(x + 1, y + 1, size - 1, size - 1);
         g.setColor(Color.LIGHT_GRAY);
         g.drawRect(x, y, size, size);
diff --git a/ch15/GridCanvas.java b/ch15/GridCanvas.java
@@ -78,7 +78,7 @@ public int test(int r, int c) {
             if (array[r][c].isOn()) {
                 return 1;
             }
-        } catch (IndexOutOfBoundsException e) {
+        } catch (ArrayIndexOutOfBoundsException e) {
             // cell doesn't exist
         }
         return 0;
diff --git a/ch15/Langton.java b/ch15/Langton.java
@@ -26,30 +26,25 @@ public Langton(int rows, int cols) {
     public void update() {
 
         Cell cell = grid.cellAt(xpos, ypos);
-        if (cell.isOn()) {
-            // at a black square; flip color and turn left
-            cell.turnOff();
-            head = (head + 3) % 4;
-        } else {
-            // at a white square; flip color and turn right
-            cell.turnOn();
+        if (cell.isOff()) {
+            // at a white square; turn right and flip color
             head = (head + 1) % 4;
+            cell.turnOn();
+        } else {
+            // at a black square; turn left and flip color
+            head = (head + 3) % 4;
+            cell.turnOff();
         }
 
         // move forward one unit
-        switch (head) {
-            case 0:
-                ypos -= 1;
-                break;
-            case 1:
-                xpos += 1;
-                break;
-            case 2:
-                ypos += 1;
-                break;
-            case 3:
-                xpos -= 1;
-                break;
+        if (head == 0) {
+            ypos -= 1;
+        } else if (head == 1) {
+            xpos += 1;
+        } else if (head == 2) {
+            ypos += 1;
+        } else {
+            xpos -= 1;
         }
 
         // TODO: draw a triangle to show the ant
diff --git a/ch15/empty.cells b/ch15/empty.cells
@@ -0,0 +1,11 @@
+!An empty 10x10 grid
+..........
+..........
+..........
+..........
+..........
+..........
+..........
+..........
+..........
+..........

Original file line number	Diff line number	Diff line change
`@@ -78,7 +78,7 @@ public int test(int r, int c) {`
`78`	`78`	`if (array[r][c].isOn()) {`
`79`	`79`	`return 1;`
`80`	`80`	`}`
`81`		`- } catch (IndexOutOfBoundsException e) {`
	`81`	`+ } catch (ArrayIndexOutOfBoundsException e) {`
`82`	`82`	`// cell doesn't exist`
`83`	`83`	`}`
`84`	`84`	`return 0;`