Add all 23 GoF design pattern implementations

03-behavioral/iterator/Book.java

@@ -0,0 +1,14 @@
+package iterator;
+
+public class Book {
+    private final String title;
+    private final String author;
+    private final int year;
+
+    public Book(String title, String author, int year) {
+        this.title = title; this.author = author; this.year = year;
+    }
+    public String getTitle()  { return title; }
+    public int    getYear()   { return year; }
+    @Override public String toString() { return "\"" + title + "\" by " + author + " (" + year + ")"; }
+}