diff --git a/w3/BankAccount.class b/w3/BankAccount.class
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Binary files /dev/null and b/w3/BankAccount.class differ
diff --git a/w3/BankAccount.java b/w3/BankAccount.java
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+++ b/w3/BankAccount.java
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+public class BankAccount {
+    // 1. 定义私有属性，符合封装原则，外部无法直接访问
+    private final String accountNumber; // 账户号：创建后不可修改，用final修饰（也可在setter中做限制）
+    private String ownerName;           // 户主姓名：可修改
+    private double balance;            // 余额：只能通过方法修改
+
+    /**
+     * 2. 构造方法：创建账户时必须传入账户号和户主姓名，初始余额为0
+     */
+    public BankAccount(String accountNumber, String ownerName) {
+        this.accountNumber = accountNumber;
+        this.ownerName = ownerName;
+        this.balance = 0.0; // 初始余额为0
+    }
+
+    /**
+     * 3. 存款操作
+     * @param amount 存款金额
+     */
+    public void deposit(double amount) {
+        if (amount > 0) { // 金额必须大于0
+            balance += amount;
+            System.out.println("存款成功！当前余额：" + balance);
+        } else {
+            System.out.println("存款失败：金额必须大于0！");
+        }
+    }
+
+    /**
+     * 4. 取款操作
+     * @param amount 取款金额
+     */
+    public void withdraw(double amount) {
+        if (amount > 0) { // 金额大于0
+            if (amount <= balance) { // 不超过当前余额
+                balance -= amount;
+                System.out.println("取款成功！当前余额：" + balance);
+            } else {
+                System.out.println("取款失败：余额不足！");
+            }
+        } else {
+            System.out.println("取款失败：金额必须大于0！");
+        }
+    }
+
+    /**
+     * 5. 查询余额：对外提供查询方法，不允许直接修改
+     */
+    public double getBalance() {
+        return balance;
+    }
+
+    /**
+     * 6. Getter & Setter 方法
+     * - accountNumber 不提供setter，保证不可修改
+     * - ownerName 提供setter，允许修改
+     */
+    public String getAccountNumber() {
+        return accountNumber;
+    }
+
+    public String getOwnerName() {
+        return ownerName;
+    }
+
+    public void setOwnerName(String ownerName) {
+        this.ownerName = ownerName;
+    }
+
+    // 测试类
+    public static void main(String[] args) {
+        // 创建账户
+        BankAccount account = new BankAccount("622202123456789", "张三");
+
+        // 测试存款
+        account.deposit(1000.0); // 存款1000
+
+        // 测试取款
+        account.withdraw(300.0);  // 取款300
+
+        // 测试余额不足取款
+        account.withdraw(800.0);  // 余额不足，失败
+
+        // 测试修改户主姓名
+        account.setOwnerName("张三三");
+        System.out.println("修改后的户主姓名：" + account.getOwnerName());
+
+        // 尝试直接修改余额（编译报错，验证封装）
+        // account.balance = 0; // 错误：balance是private属性，无法直接访问
+    }
+}
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