Flood algorithm added and (basic) tests performed.

src/main/java/ca/recrown/islandsurvivalcraft/floodfill/Floodable.java

@@ -0,0 +1,14 @@
+package ca.recrown.islandsurvivalcraft.floodfill;
+
+import ca.recrown.islandsurvivalcraft.types.Point2;
+
+public interface Floodable {
+    /**
+     * Called for every block. If it shouldn't be flooded, return false.
+     * Code to execute for flooding should be placed here.
+     * @param x the x coordinate.
+     * @param y the y coordinate.
+     * @return if this was a successful flooding.
+     */
+    public boolean flood(Point2 point);
+}

src/main/java/ca/recrown/islandsurvivalcraft/floodfill/Flooder.java

@@ -0,0 +1,43 @@
+package ca.recrown.islandsurvivalcraft.floodfill;
+
+import java.util.HashSet;
+import java.util.LinkedList;
+
+import ca.recrown.islandsurvivalcraft.types.Point2;
+
+public class Flooder {
+    private final HashSet<Point2> checked = new HashSet<>();
+    private final Point2 start;
+    private final Floodable floodable;
+
+    public Flooder(Point2 start, Floodable floodable) {
+        this.start = start;
+        this.floodable = floodable;
+    }
+
+    public Flooder(int xStart, int yStart, Floodable floodable) {
+        this(new Point2(xStart, yStart),  floodable);
+    }
+
+    public void start() {
+        if (!checked.add(start)) return;
+        if (!floodable.flood(start)) return;
+        LinkedList<Point2> queue = new LinkedList<>();
+        queue.add(start);
+        while (!queue.isEmpty()) {
+            Point2 p = queue.pop();
+
+            Point2 pE = new Point2(p.x + 1, p.y);
+            if (floodable.flood(pE)) queue.add(pE);
+
+            Point2 pW = new Point2(p.x - 1, p.y);
+            if (floodable.flood(pW)) queue.add(pW);
+
+            Point2 pN = new Point2(p.x, p.y + 1);
+            if (floodable.flood(pN)) queue.add(pN);
+
+            Point2 pS = new Point2(p.x, p.y - 1);
+            if (floodable.flood(pS)) queue.add(pS);
+        }
+    }
+}