diff --git a/com/study/demo3/Bicycle.class b/com/study/demo3/Bicycle.class
new file mode 100644
index 0000000..8cb0107
Binary files /dev/null and b/com/study/demo3/Bicycle.class differ
diff --git a/com/study/demo3/Bicycle.java b/com/study/demo3/Bicycle.java
new file mode 100644
index 0000000..5a2d76a
--- /dev/null
+++ b/com/study/demo3/Bicycle.java
@@ -0,0 +1,7 @@
+package com.study.demo3;
+public class Bicycle extends Vehicle {
+    @Override
+    public void start() {
+        System.out.println("The bike is started");
+    }
+}
diff --git a/com/study/demo3/Book.class b/com/study/demo3/Book.class
new file mode 100644
index 0000000..3c8d5f2
Binary files /dev/null and b/com/study/demo3/Book.class differ
diff --git a/com/study/demo3/Book.java b/com/study/demo3/Book.java
new file mode 100644
index 0000000..bcb0cc2
--- /dev/null
+++ b/com/study/demo3/Book.java
@@ -0,0 +1,61 @@
+package com.study.demo3;
+
+public class Book {
+    protected String isbn;
+    protected String title;
+    protected boolean available;
+
+   
+    public Book() {
+        this.available = true;
+    }
+
+   
+    public Book(String isbn, String title) {
+        this.isbn = isbn;
+        this.title = title;
+        this.available = true;
+    }
+
+   
+    public Book(String isbn, String title, boolean available) {
+        this.isbn = isbn;
+        this.title = title;
+        this.available = available;
+    }
+
+   
+    public String getIsbn() {
+        return isbn;
+    }
+
+    public void setIsbn(String isbn) {
+        this.isbn = isbn;
+    }
+
+    public String getTitle() {
+        return title;
+    }
+
+    public void setTitle(String title) {
+        this.title = title;
+    }
+
+    public boolean isAvailable() {
+        return available;
+    }
+
+    public void setAvailable(boolean available) {
+        this.available = available;
+    }
+
+   
+    public void returnBook() {
+        if (!this.available) {
+            this.available = true;
+            System.out.println(this.title + " (ISBN: " + this.isbn + ") has been returned and is now available.");
+        } else {
+            System.out.println(this.title + " (ISBN: " + this.isbn + ") is already available.");
+        }
+    }
+}
diff --git a/com/study/demo3/Car.class b/com/study/demo3/Car.class
new file mode 100644
index 0000000..7a34b27
Binary files /dev/null and b/com/study/demo3/Car.class differ
diff --git a/com/study/demo3/Car.java b/com/study/demo3/Car.java
new file mode 100644
index 0000000..91dc698
--- /dev/null
+++ b/com/study/demo3/Car.java
@@ -0,0 +1,8 @@
+package com.study.demo3;
+public class Car extends Vehicle {
+    @Override
+   
+    public void start() {
+        System.out.println("The car is started");
+    }
+}
diff --git a/com/study/demo3/EBook.class b/com/study/demo3/EBook.class
new file mode 100644
index 0000000..4800637
Binary files /dev/null and b/com/study/demo3/EBook.class differ
diff --git a/com/study/demo3/EBook.java b/com/study/demo3/EBook.java
new file mode 100644
index 0000000..ccbac3f
--- /dev/null
+++ b/com/study/demo3/EBook.java
@@ -0,0 +1,30 @@
+package com.study.demo3;
+public class EBook extends Book {
+    private double fileSize;
+
+   
+    public EBook() {
+        super();
+    }
+
+   
+   
+    public EBook(String isbn, String title, double fileSize) {
+        super(isbn, title);
+        this.fileSize = fileSize;
+    }
+
+   
+    public double getFileSize() {
+        return fileSize;
+    }
+
+    public void setFileSize(double fileSize) {
+        this.fileSize = fileSize;
+    }
+
+    @Override
+    public String toString() {
+        return "EBook [ISBN=" + isbn + ", Title=" + title + ", FileSize=" + fileSize + "MB, Available=" + available + "]";
+    }
+}
diff --git a/com/study/demo3/Library.class b/com/study/demo3/Library.class
new file mode 100644
index 0000000..ce16e21
Binary files /dev/null and b/com/study/demo3/Library.class differ
diff --git a/com/study/demo3/Library.java b/com/study/demo3/Library.java
new file mode 100644
index 0000000..b64d39c
--- /dev/null
+++ b/com/study/demo3/Library.java
@@ -0,0 +1,42 @@
+package com.study.demo3;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.ArrayList;
+
+public class Library {
+   
+    private Map<String, Book> books;
+
+    public Library() {
+        this.books = new HashMap<>();
+    }
+
+   
+   
+    public void addBook(Book b) {
+        String isbn = b.getIsbn();
+
+       
+        if (books.containsKey(isbn)) {
+            System.out.println("The book already exists, adding it failed.");
+        } else {
+            books.put(isbn, b);
+            System.out.println("Book added successfully: " + b.getTitle());
+        }
+    }
+
+   
+   
+    public List<Book> searchAvailableBooks() {
+        List<Book> availableBooks = new ArrayList<>();
+        
+       
+        for (Book book : books.values()) {
+            if (book.isAvailable()) {
+                availableBooks.add(book);
+            }
+        }
+        return availableBooks;
+    }
+}
diff --git a/com/study/demo3/LibraryTest.class b/com/study/demo3/LibraryTest.class
new file mode 100644
index 0000000..25a3772
Binary files /dev/null and b/com/study/demo3/LibraryTest.class differ
diff --git a/com/study/demo3/LibraryTest.java b/com/study/demo3/LibraryTest.java
new file mode 100644
index 0000000..46baa61
--- /dev/null
+++ b/com/study/demo3/LibraryTest.java
@@ -0,0 +1,44 @@
+package com.study.demo3;
+import java.util.List;
+
+public class LibraryTest {
+    public static void main(String[] args) {
+        Library lib = new Library();
+
+       
+        EBook e1 = new EBook("E001", "Java Basics", 5.2);
+       
+        e1.setAvailable(false); 
+
+       
+        PrintedBook p1 = new PrintedBook("P001", "Design Patterns", 3);
+
+       
+        lib.addBook(e1);
+        lib.addBook(p1);
+
+       
+        lib.addBook(p1);
+
+       
+        System.out.println("\n--- 可借阅图书列表 (available = true) ---");
+        List<Book> availableList = lib.searchAvailableBooks();
+
+        if (availableList.isEmpty()) {
+            System.out.println("No books are currently available for loan.");
+        } else {
+            for (Book book : availableList) {
+               
+                System.out.println("- " + book.getTitle() + " (ISBN: " + book.getIsbn() + ")");
+            }
+        }
+        
+       
+        e1.returnBook(); 
+        System.out.println("\n--- 恢复 e1 后可借阅图书列表 ---");
+        availableList = lib.searchAvailableBooks();
+        for (Book book : availableList) {
+            System.out.println("- " + book.getTitle() + " (ISBN: " + book.getIsbn() + ")");
+        }
+    }
+}
diff --git a/com/study/demo3/Main2.class b/com/study/demo3/Main2.class
new file mode 100644
index 0000000..fadc973
Binary files /dev/null and b/com/study/demo3/Main2.class differ
diff --git a/com/study/demo3/Main3.java b/com/study/demo3/Main3.java
new file mode 100644
index 0000000..1d41593
--- /dev/null
+++ b/com/study/demo3/Main3.java
@@ -0,0 +1,34 @@
+package com.study.demo3;
+public class Main {
+    public static void main(String[] args) {
+       
+        System.out.println("--- 测试 EBook ---");
+       
+        EBook ebook = new EBook("123-456", "Java Programming", 2.5);
+        System.out.println("EBook Status (Initial): " + ebook.toString());
+
+       
+        ebook.setAvailable(false);
+        System.out.println("EBook Status (Borrowed): " + ebook.toString());
+
+       
+        ebook.returnBook();
+        System.out.println("EBook Status (After Return): " + ebook.toString());
+
+       
+        System.out.println("\n--- 测试 PrintedBook ---");
+        PrintedBook pbook = new PrintedBook();
+        pbook.setIsbn("789-012");
+        pbook.setTitle("Python Guide");
+        pbook.setStock(10);
+        System.out.println("PBook Status (Initial): " + pbook.toString());
+
+       
+        pbook.setAvailable(false);
+        System.out.println("PBook Status (Borrowed): " + pbook.toString());
+
+       
+        pbook.returnBook();
+        System.out.println("PBook Status (After Return): " + pbook.toString());
+    }
+}
diff --git a/com/study/demo3/PrintedBook.class b/com/study/demo3/PrintedBook.class
new file mode 100644
index 0000000..2583d90
Binary files /dev/null and b/com/study/demo3/PrintedBook.class differ
diff --git a/com/study/demo3/PrintedBook.java b/com/study/demo3/PrintedBook.java
new file mode 100644
index 0000000..18f9be1
--- /dev/null
+++ b/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 + "]";
+    }
+}
diff --git a/com/study/demo3/StudentManager.class b/com/study/demo3/StudentManager.class
new file mode 100644
index 0000000..4e06966
Binary files /dev/null and b/com/study/demo3/StudentManager.class differ
diff --git a/com/study/demo3/StudentManager.java b/com/study/demo3/StudentManager.java
new file mode 100644
index 0000000..be20826
--- /dev/null
+++ b/com/study/demo3/StudentManager.java
@@ -0,0 +1,28 @@
+package com.study.demo3;
+import java.util.*;
+
+public class StudentManager {
+    public static void main(String[] args) {
+        List<String> studentNames = new ArrayList<>();
+        Map<String, Integer> studentScores = new HashMap<>();
+
+        studentNames.add("张三");
+        studentNames.add("李四");
+        studentNames.add("王五");
+
+        studentScores.put("张三", 85);
+        studentScores.put("李四", 77);
+        studentScores.put("王五", 99);
+
+        System.out.println("--- 所有学生姓名 ---");
+        for (String name : studentNames) {
+            System.out.println(name);
+        }
+
+        studentScores.put("张三", 70);
+
+        Integer zhangsanScore = studentScores.get("张三");
+        System.out.println("\n--- 修改后张三的成绩 ---");
+        System.out.println("张三的成绩: " + zhangsanScore);
+    }
+}
diff --git a/com/study/demo3/Train.class b/com/study/demo3/Train.class
new file mode 100644
index 0000000..2405a80
Binary files /dev/null and b/com/study/demo3/Train.class differ
diff --git a/com/study/demo3/Train.java b/com/study/demo3/Train.java
new file mode 100644
index 0000000..d99c2ff
--- /dev/null
+++ b/com/study/demo3/Train.java
@@ -0,0 +1,7 @@
+package com.study.demo3;
+public class Train extends Vehicle {
+    @Override
+    public void start() {
+        System.out.println("The train is started");
+    }
+}
diff --git a/com/study/demo3/Vehicle.class b/com/study/demo3/Vehicle.class
new file mode 100644
index 0000000..fba2811
Binary files /dev/null and b/com/study/demo3/Vehicle.class differ
diff --git a/com/study/demo3/Vehicle.java b/com/study/demo3/Vehicle.java
new file mode 100644
index 0000000..7d86d57
--- /dev/null
+++ b/com/study/demo3/Vehicle.java
@@ -0,0 +1,20 @@
+package com.study.demo3;
+public class Vehicle {
+    protected String name;
+
+    public Vehicle(String name) {
+        this.name = name;
+    }
+    
+    public Vehicle() {
+        this.name = "Unknown Vehicle";
+    }
+
+    public void start() {
+        System.out.println("Vehicle Start");
+    }
+
+    public void stop() {
+        System.out.println("Vehicle Stop");
+    }
+}