update:demo3

com/study/demo3/PrintedBook.java

@@ -0,0 +1,29 @@
+package com.study.demo3;
+public class PrintedBook extends Book {
+    private int stock;
+
+   
+    public PrintedBook() {
+        super();
+    }
+
+   
+    public PrintedBook(String isbn, String title, int stock) {
+        super(isbn, title);
+        this.stock = stock;
+    }
+
+   
+    public int getStock() {
+        return stock;
+    }
+
+    public void setStock(int stock) {
+        this.stock = stock;
+    }
+
+    @Override
+    public String toString() {
+        return "PrintedBook [ISBN=" + isbn + ", Title=" + title + ", Stock=" + stock + ", Available=" + available + "]";
+    }
+}