上传文件至 'w7'

w7/BankAccount.java

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+/**
+ * 任务二：银行取款自定义异常
+ * 文件内含：InsufficientFundsException + Account + main 测试
+ */
+
+// ── 自定义异常：继承 Exception（Checked，强迫调用方处理）──
+class InsufficientFundsException extends Exception {
+    private final double balance;   // 当前余额
+    private final double amount;    // 尝试取款金额
+
+    public InsufficientFundsException(double balance, double amount) {
+        super(String.format("余额不足！当前余额 %.2f 元，尝试取款 %.2f 元，差额 %.2f 元",
+                balance, amount, amount - balance));
+        this.balance = balance;
+        this.amount  = amount;
+    }
+
+    public double getBalance() { return balance; }
+    public double getAmount()  { return amount; }
+}
+
+// ── Account 类 ──
+class Account {
+    private final String owner;
+    private double balance;
+
+    public Account(String owner, double initialBalance) {
+        this.owner   = owner;
+        this.balance = initialBalance;
+    }
+
+    /**
+     * 取款：余额不足时抛出 InsufficientFundsException，并携带当前余额信息
+     */
+    public void withdraw(double amount) throws InsufficientFundsException {
+        if (amount <= 0) {
+            throw new IllegalArgumentException("取款金额必须大于 0");
+        }
+        if (amount > balance) {
+            throw new InsufficientFundsException(balance, amount);
+        }
+        balance -= amount;
+        System.out.printf("  取款成功：%.2f 元，剩余余额：%.2f 元%n", amount, balance);
+    }
+
+    public double getBalance() { return balance; }
+    public String getOwner()   { return owner; }
+}
+
+// ── 测试入口 ──
+public class BankAccount {
+    public static void main(String[] args) {
+        Account acc = new Account("张三", 500.00);
+        System.out.println("账户：" + acc.getOwner() + "，初始余额：" + acc.getBalance());
+
+        // 正常取款
+        System.out.println("\n--- 取款 200 元 ---");
+        try {
+            acc.withdraw(200);
+        } catch (InsufficientFundsException e) {
+            System.out.println("  提示：" + e.getMessage());
+        }
+
+        // 余额不足
+        System.out.println("\n--- 取款 400 元（余额不足）---");
+        try {
+            acc.withdraw(400);
+        } catch (InsufficientFundsException e) {
+            System.out.println("  提示：" + e.getMessage());
+            System.out.printf("  当前余额：%.2f 元，建议最多取 %.2f 元%n",
+                    e.getBalance(), e.getBalance());
+        }
+
+        // 非法金额
+        System.out.println("\n--- 取款 -50 元（非法金额）---");
+        try {
+            acc.withdraw(-50);
+        } catch (InsufficientFundsException e) {
+            System.out.println("  提示：" + e.getMessage());
+        } catch (IllegalArgumentException e) {
+            System.out.println("  错误：" + e.getMessage());
+        }
+    }
+}

w7/ScoreReader.java

@@ -0,0 +1,75 @@
+import java.io.*;
+import java.nio.file.*;
+
+/**
+ * 课堂练习：重构"裸奔"代码
+ * 使用 try-with-resources 确保流自动关闭，处理三类异常
+ */
+public class ScoreReader {
+
+    public static void main(String[] args) {
+        // 创建一个测试用的 scores.txt（实际场景中文件已存在）
+        createSampleFile();
+
+        System.out.println("=== 正常读取 ===");
+        readAndPrintAverage("scores.txt");
+
+        System.out.println("\n=== 文件不存在 ===");
+        readAndPrintAverage("notfound.txt");
+
+        System.out.println("\n=== 含非数字行 ===");
+        createBadFile();
+        readAndPrintAverage("bad_scores.txt");
+    }
+
+    /**
+     * 重构后的核心方法：
+     * 1. try-with-resources 自动关闭流（无需手动 br.close()）
+     * 2. 分层处理三类异常：文件不存在 / 读取错误 / 数字格式错误
+     */
+    public static void readAndPrintAverage(String filename) {
+        int sum   = 0;
+        int count = 0;
+
+        // try-with-resources：括号内声明的资源在 try 结束后自动关闭
+        try (BufferedReader br = new BufferedReader(new FileReader(filename))) {
+            String line;
+            while ((line = br.readLine()) != null) {
+                line = line.trim();
+                if (line.isEmpty()) continue;        // 跳过空行
+                try {
+                    sum += Integer.parseInt(line);   // 可能抛 NumberFormatException
+                    count++;
+                } catch (NumberFormatException e) {
+                    System.out.println("  警告：跳过非数字行 [" + line + "]");
+                }
+            }
+        } catch (FileNotFoundException e) {
+            System.out.println("  错误：文件不存在 -> " + filename);
+            return;
+        } catch (IOException e) {
+            System.out.println("  错误：文件读取失败 -> " + e.getMessage());
+            return;
+        }
+
+        if (count == 0) {
+            System.out.println("  无有效成绩数据。");
+        } else {
+            System.out.printf("  共 %d 条成绩，平均分：%.2f%n", count, (double) sum / count);
+        }
+    }
+
+    // ── 辅助：生成测试文件 ──
+    private static void createSampleFile() {
+        try (PrintWriter pw = new PrintWriter("scores.txt")) {
+            pw.println("85"); pw.println("92");
+            pw.println("78"); pw.println("90"); pw.println("88");
+        } catch (IOException ignored) {}
+    }
+
+    private static void createBadFile() {
+        try (PrintWriter pw = new PrintWriter("bad_scores.txt")) {
+            pw.println("75"); pw.println("abc"); pw.println("88");
+        } catch (IOException ignored) {}
+    }
+}