feat(w3): 完成BankAccount类封装，实现存款、取款和查询余额功能

w3/BankAccount.java

@@ -0,0 +1,63 @@
+public class BankAccount {
+    // 私有属性
+    private final String accountNumber;
+    private String ownerName;
+    private double balance;
+    
+    // 构造方法
+    public BankAccount(String accountNumber, String ownerName) {
+        this.accountNumber = accountNumber;
+        this.ownerName = ownerName;
+        this.balance = 0.0;
+    }
+    
+    // Getter 方法
+    public String getAccountNumber() {
+        return accountNumber;
+    }
+    
+    public String getOwnerName() {
+        return ownerName;
+    }
+    
+    public double getBalance() {
+        return balance;
+    }
+    
+    // Setter 方法
+    public void setOwnerName(String ownerName) {
+        this.ownerName = ownerName;
+    }
+    
+    // 存款操作
+    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("存款金额必须大于 0");
+        }
+    }
+    
+    // 取款操作
+    public void withdraw(double amount) {
+        if (amount > 0) {
+            if (amount <= balance) {
+                balance -= amount;
+                System.out.println("取款成功！当前余额：" + balance);
+            } else {
+                System.out.println("余额不足，无法取款");
+            }
+        } else {
+            System.out.println("取款金额必须大于 0");
+        }
+    }
+    
+    // 显示账户信息
+    public void displayInfo() {
+        System.out.println("账号：" + accountNumber);
+        System.out.println("户主：" + ownerName);
+        System.out.println("余额：" + balance);
+        System.out.println();
+    }
+}