diff --git a/w3/BackAccount.java b/w3/BackAccount.java
new file mode 100644
index 0000000..36c747d
--- /dev/null
+++ b/w3/BackAccount.java
@@ -0,0 +1,90 @@
+package w3;
+
+
+public class BackAccount {
+    // 内部类，不需要 public
+    static class BankAccount {
+        private final String accountNumber;
+        private String ownerName;
+        private double balance;
+
+        public BankAccount(String accountNumber, String ownerName) {
+            this.accountNumber = accountNumber;
+            this.ownerName = ownerName;
+            this.balance = 0;
+        }
+
+        public void deposit(double amount) {
+            if (amount > 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！");
+            }
+        }
+
+        public void withdraw(double amount) {
+            if (amount > 0 && amount <= balance) {
+                balance -= amount;
+                System.out.println("取款成功！当前余额：" + balance);
+            } else {
+                System.out.println("取款失败：金额无效或余额不足！");
+            }
+        }
+
+        public double getBalance() {
+            return balance;
+        }
+
+        public void setOwnerName(String newName) {
+            ownerName = newName;
+            System.out.println("户主姓名已修改为：" + ownerName);
+        }
+
+        public String getAccountNumber() {
+            return accountNumber;
+        }
+
+        public String getOwnerName() {
+            return ownerName;
+        }
+    }
+
+    public static void main(String[] args) {
+        // 创建账户
+        BankAccount account = new BankAccount("123456789", "张三");
+        System.out.println("=== 创建银行账户 ===");
+        System.out.println("账号：" + account.getAccountNumber());
+        System.out.println("户主：" + account.getOwnerName());
+        System.out.println("初始余额：" + account.getBalance());
+        System.out.println();
+
+        // 测试存款功能
+        System.out.println("=== 存款测试 ===");
+        account.deposit(1000);
+        account.deposit(-200);
+        account.deposit(500);
+        System.out.println("当前余额：" + account.getBalance());
+        System.out.println();
+
+        // 测试取款功能
+        System.out.println("=== 取款测试 ===");
+        account.withdraw(300);
+        account.withdraw(1500);
+        account.withdraw(-100);
+        System.out.println("当前余额：" + account.getBalance());
+        System.out.println();
+
+        // 测试修改户主姓名
+        System.out.println("=== 修改户主信息 ===");
+        account.setOwnerName("李四");
+        System.out.println("当前户主：" + account.getOwnerName());
+        System.out.println();
+
+        // 最终账户信息
+        System.out.println("=== 账户最终状态 ===");
+        System.out.println("账号：" + account.getAccountNumber());
+        System.out.println("户主：" + account.getOwnerName());
+        System.out.println("余额：" + account.getBalance());
+    }
+}
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