refactor

library/Test.java

@@ -0,0 +1,15 @@
+package library;
+
+public class Test {
+    public static void main(String[] args) {
+        Administrator adm = new Administrator(1, "John");
+        adm.getLib().add(new Book("123", "Book1", 1));
+        adm.getLib().add(new Book("124", "Book2", 1));
+        adm.getLib().add(new Book("125", "Book3", 1));
+        Student st = new Student(1, "Alice");
+        st.getBg().add(new Book("123", "Book1", 1));
+        st.getBg().add(new Book("124", "Book2", 1));
+        st.getBg().add(new Book("125", "Book3", 1));
+        adm.register(st);
+    }
+}