Movement kinda works.

twentyfortyeight/src/twentyfortyeight/Main.java

@@ -80,12 +80,11 @@ class Game extends World {
     }
 
     public void onKeyEvent(String key) {
-        System.out.println("YES");
-        if (key.equals("left") || key.equals("h")) this.grid.move(0);
-        else if (key.equals("down") || key.equals("j")) this.grid.move(1);
-        else if (key.equals("up") || key.equals("k")) this.grid.move(2);
-        else if (key.equals("right") || key.equals("l")) this.grid.move(3);
-        else return;
+        if (key.equals("left") || key.equals("h")) this.grid.mv(0);
+        else if (key.equals("down") || key.equals("j")) this.grid.mv(1);
+        else if (key.equals("up") || key.equals("k")) this.grid.mv(2);
+        else if (key.equals("right") || key.equals("l")) this.grid.mv(3);
+        else return; // Don't draw if bad key pressed.
         this.draw();
     }
 
@@ -148,20 +147,65 @@ class Grid {
     // Get the y coord for an index.
     int iy(int i) { return i % this.w; }
 
+    // Given an index and a direction, is there a free there?
+    boolean freeDir(int i, int d) {
+        if (d == 0) {                               // Left.
+            if ((i - 1) % this.w < 0) return false; // At an edge.
+            return this.buf.get(i - 1) == 0;
+        } else if (d == 1) {                          // Down.
+            if ((i + this.w) > this.sz) return false; // At an edge
+            return this.buf.get(i + this.w) == 0;
+        } else if (d == 2) { // Up.
+            if ((i - this.w) < 0) return false;
+            return this.buf.get(i - this.w) == 0;
+        } else if (d == 3) {                         // Right.
+            if ((i + 1) % this.w == 0) return false; // At an edge.
+            return this.buf.get(i + 1) ==
+                0; // Check if next space over is free.
+        }
+
+        else
+            throw new IllegalArgumentException("Bad direction code given.");
+    }
+
+    // Get the indexes of all moveable tiles in a given direction -- those
+    // that are abutted by a free cell in the specified direction.
+    List<Integer> mvblDir(int d) {
+        List<Integer> mvbl = new ArrayList<Integer>();
+
+        for (int i : this.unfreeCellIdxs())
+            if (this.freeDir(i, d)) mvbl.add(i);
+
+        return mvbl;
+    }
+
+    // Move the tile at the index 1 space in the specified direction.
+    void mvTile(int i, int d) {
+        if (d == 0) this.buf.set(i - 1, this.buf.get(i));
+        else if (d == 1) this.buf.set(i + this.w, this.buf.get(i));
+        else if (d == 2) this.buf.set(i - this.w, this.buf.get(i));
+        else if (d == 3) this.buf.set(i + 1, this.buf.get(i));
+        else throw new IllegalArgumentException("Bad direction code given.");
+
+        this.buf.set(i, 0); // Reset original.
+    }
+
+    // Partial move -- apply movement rules once. There still may be tiles
+    // which can move after this is done. Return true if there are still
+    // more moves possible.
+    boolean partMv(int d) {
+        // 1. Find the tiles that can move.
+        List<Integer> mvbl = this.mvblDir(d);
+        if (mvbl.isEmpty()) return false;
+        // 2. Move each tile to its new location.
+        for (int i : mvbl) { this.mvTile(i, d); }
+        return true;
+    }
+
     // Move all tiles in that direction until they can't move or combine any
     // more.
-    void move(int d) {
-        // TODO: Don't assume right.
-        // Assume right.
-        List<Integer> unfrees = this.unfreeCellIdxs();
-        List<Integer> frees = this.freeCellIdxs();
-        for (int unfree : unfrees) {
-            /*
-            if (frees.contains(this.ix(unfree) + 1)) {
-                this.buf.set(unfree, 0))
-            }
-            */
-        }
+    void mv(int d) {
+        while (this.partMv(d)); // I love side effects :).
     }
 
     // Render the grid.
@@ -231,44 +275,9 @@ class Examples {
         t.checkExpect(regular.get(3, 3), 0);
     }
 
-    /*
-    void testMoveRight(Tester t) {
-        init();
-        regular.set(1, 0, 16)
-            .set(2, 0, 16)
-            .set(3, 0, 32)
-            .set(0, 1, 4)
-            .set(1, 1, 4)
-            .set(4, 1, 2);
-
-        // Move right.
-        regular.move(2);
-
-        t.checkExpect(regular.get(2, 0), 32);
-        t.checkExpect(regular.get(3, 0), 32);
-        t.checkExpect(regular.get(2, 1), 8);
-        t.checkExpect(regular.get(3, 1), 2);
-    }
-    */
-
     void testGame(Tester t) {
         game = new Game();
         game.grid.set(0, 0, 2);
-        game.grid.set(0, 1, 4);
-        // Random free space.
-        game.grid.set(0, 3, 8);
-        game.grid.set(1, 0, 16);
-        game.grid.set(1, 1, 32);
-        game.grid.set(1, 2, 64);
-        game.grid.set(1, 3, 128);
-        game.grid.set(2, 0, 256);
-        game.grid.set(2, 1, 512);
-        game.grid.set(2, 2, 1024);
-        game.grid.set(2, 3, 2048);
-        game.grid.set(3, 0, 4096);
-        // Random free space.
-        game.grid.set(3, 2, 8192);
-        game.grid.set(3, 3, 16384);
 
         game.launchGame();
     }