Added Block.getPistonMoveReaction, BlockPistonExtend and BlockPistonRetractEvent

src/main/java/org/bukkit/event/block/BlockPistonExtendEvent.java

@@ -0,0 +1,43 @@
+package org.bukkit.event.block;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+
+import org.bukkit.block.Block;
+
+public class BlockPistonExtendEvent extends BlockPistonEvent {
+    private int length;
+    private List<Block> blocks;
+
+    public BlockPistonExtendEvent(Block block, int length) {
+        super(Type.BLOCK_PISTON_EXTEND, block);
+
+        this.length = length;
+    }
+
+    /**
+     * Get the amount of blocks which will be moved while extending.
+     *
+     * @return the amount of moving blocks
+     */
+    public int getLength() {
+        return this.length;
+    }
+
+    /**
+     * Get an immutable list of the blocks which will be moved by the extending.
+     *
+     * @return Immutable list of the moved blocks.
+     */
+    public List<Block> getBlocks() {
+        if (blocks == null) {
+            ArrayList<Block> tmp = new ArrayList<Block>();
+            for (int i = 0; i < this.getLength(); i++) {
+                tmp.add(block.getRelative(getDirection(), i + 1));
+            }
+            blocks = Collections.unmodifiableList(tmp);
+        }
+        return blocks;
+    }
+}