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Semester 1/Programming 1/Java/examples/projects/chapter07/automaton-v4/Automaton.java

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+import java.util.*;
+
+/**
+ * Model a 1D elementary cellular automaton.
+ * 
+ * @author David J. Barnes and Michael Kölling
+ * @version  2016.02.29 - version 4
+ */
+public class Automaton
+{
+    // The number of cells.
+    private final int numberOfCells;
+    // The state of the cells.
+    private int[] state;
+    // The state table encoding the next-state changes.
+    private int[] stateTable;
+    
+    /**
+     * Create a 1D automaton consisting of the given number of cells.
+     * @param numberOfCells The number of cells in the automaton.
+     */
+    public Automaton(int numberOfCells)
+    {
+        this.numberOfCells = numberOfCells;
+        // Allow an extra element to avoid 'fencepost' errors.
+        state = new int[numberOfCells + 1];
+        stateTable = new int[] {
+            0, 1, 0, 0, 1, 0, 0, 1, // Wolfram code 146
+        };
+        // Seed the automaton with a single 'on' cell.
+        state[numberOfCells / 2] = 1;
+    }
+    
+    /**
+     * Print the current state of the automaton.
+     */
+    public void print()
+    {
+        for(int cellValue : state) {
+            System.out.print(cellValue == 1 ? "*" : " ");
+        }
+        System.out.println();
+    }   
+    
+    /**
+     * Update the automaton to its next state.
+     */
+    public void update()
+    {
+        // Build the new state in a separate array.
+        int[] nextState = new int[state.length];
+        // Use 0 for the non-existent value to the left of
+        // the first cell.
+        int left = 0;
+        int center = state[0];
+        for(int i = 0; i < numberOfCells; i++) {
+            int right = state[i + 1];
+            nextState[i] = calculateNextState(left, center, right);
+            left = center;
+            center = right;
+        }
+        state = nextState;
+    }
+    
+    /**
+     * Reset the automaton.
+     */
+    public void reset()
+    {
+        Arrays.fill(state, 0);
+        // Seed the automaton with a single 'on' cell in the middle.
+        state[numberOfCells / 2] = 1;
+    }
+
+    /**
+     * Calculate the next state of the center cell
+     * given current left, center and right cell
+     * values.
+     * This implements Wolfram code 110.
+     * @see https://en.wikipedia.org/wiki/Wolfram_code
+     * @param left The state of the cell to the left of center.
+     * @param center The state of the center cell.
+     * @param right The state of the cell to the right of center.
+     * @return The new value of center (0 or 1).
+     */
+    private int calculateNextState(int left, int center, int right)
+    {
+        return stateTable[encodeTriplet(left, center, right)];
+    }
+    
+    /**
+     * Encode the 1/0 triplet (left, center, right) as an
+     * integer value in the range 0-7.
+     * @param left The state of the cell to the left of center (0 or 1).
+     * @param center The state of the center cell (0 or 1).
+     * @param right The state of the cell to the right of center (0 or 1).
+     * @return (left,center,right) interpreted as a 3-bit value.
+     */
+    private int encodeTriplet(int left, int center, int right)
+    {
+        return left * 4 + center * 2 + right;
+    }
+
+}