Add all 23 GoF design pattern implementations

02-structural/composite/FileSystemItem.java

@@ -0,0 +1,10 @@
+package composite;
+/**
+ * Component — the common interface for both files (leaves) and directories (composites).
+ * Clients work through this interface and never need to know which type they're dealing with.
+ */
+public interface FileSystemItem {
+    String getName();
+    long getSize();           // total size in bytes — recursive for directories
+    void print(String indent); // display the tree at the given indentation level
+}