added command sample

command/src/main/java/com/iluwatar/ShrinkSpell.java

@@ -0,0 +1,32 @@
+package com.iluwatar;
+
+public class ShrinkSpell extends Command {
+
+	private Size oldSize;
+	
+	private Target target;
+	
+	public ShrinkSpell() {
+		oldSize = null;
+		target = null;
+	}
+	
+	@Override
+	public void execute(Target target) {
+		oldSize = target.getSize();
+		target.setSize(Size.SMALL);
+		this.target = target;
+	}
+
+	@Override
+	public void undo() {
+		if (oldSize != null && target != null) {
+			target.setSize(oldSize);
+		}
+	}
+
+	@Override
+	public String toString() {
+		return "Shrink spell";
+	}
+}