Add SimpleBudgetTracker Java sample project

SimpleBudgetTracker/README.md

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+# Simple Budget Tracker
+
+一个适合初学者的 Java 命令行记账小项目，演示类、枚举、集合、文件读写和命令行交互等基础知识。
+
+## 功能
+- 添加收入或支出记录。
+- 查看全部记录。
+- 查看统计信息（总收入、总支出、净资产）。
+- 将记录保存到本地文件并在程序启动时自动加载。
+
+## 项目结构
+```
+SimpleBudgetTracker/
+├── README.md
+├── data/
+│   └── transactions.txt
+└── src/
+    └── com/example/budget/
+        ├── TransactionType.java
+        ├── Transaction.java
+        ├── BudgetManager.java
+        ├── StorageUtil.java
+        └── Main.java
+```
+
+## 运行步骤
+1. 安装 JDK 11 或更高版本，并确保 `java` 与 `javac` 可在终端运行。
+2. 在项目根目录执行以下命令编译：
+   ```bash
+   javac -d out src/com/example/budget/*.java
+   ```
+3. 运行程序：
+   ```bash
+   java -cp out com.example.budget.Main
+   ```
+4. 根据命令行提示进行操作。程序会自动读取和保存 `data/transactions.txt` 文件。
+
+## VS Code 运行提示
+- 安装 Extension Pack for Java。
+- 打开 `Main.java` 并点击右上角的 “Run” 图标即可运行。
+- 或者在 VS Code 终端中执行上述命令。
+
+祝学习愉快！

SimpleBudgetTracker/src/com/example/budget/BudgetManager.java

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+package com.example.budget;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class BudgetManager {
+    private final List<Transaction> transactions;
+
+    public BudgetManager() {
+        this.transactions = new ArrayList<>();
+    }
+
+    public void addTransaction(Transaction transaction) {
+        transactions.add(transaction);
+    }
+
+    public List<Transaction> getAllTransactions() {
+        return transactions;
+    }
+
+    public double getTotalIncome() {
+        return transactions.stream()
+                .filter(t -> t.getType() == TransactionType.INCOME)
+                .mapToDouble(Transaction::getAmount)
+                .sum();
+    }
+
+    public double getTotalExpense() {
+        return transactions.stream()
+                .filter(t -> t.getType() == TransactionType.EXPENSE)
+                .mapToDouble(Transaction::getAmount)
+                .sum();
+    }
+
+    public double getNetBalance() {
+        return getTotalIncome() - getTotalExpense();
+    }
+
+    public void printSummary() {
+        System.out.println("========== Summary ==========");
+        System.out.printf("Total Income : %.2f%n", getTotalIncome());
+        System.out.printf("Total Expense: %.2f%n", getTotalExpense());
+        System.out.printf("Net Balance  : %.2f%n", getNetBalance());
+        System.out.println("=============================");
+    }
+}

SimpleBudgetTracker/src/com/example/budget/Main.java

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+package com.example.budget;
+
+import java.util.Scanner;
+
+public class Main {
+    private static final String DATA_FILE = "data/transactions.txt";
+
+    public static void main(String[] args) {
+        BudgetManager manager = new BudgetManager();
+        StorageUtil.loadTransactions(manager, DATA_FILE);
+
+        Scanner scanner = new Scanner(System.in);
+        boolean running = true;
+
+        while (running) {
+            printMenu();
+            System.out.print("请选择操作：");
+            String choice = scanner.nextLine().trim();
+
+            switch (choice) {
+                case "1":
+                    addTransaction(manager, scanner, TransactionType.INCOME);
+                    break;
+                case "2":
+                    addTransaction(manager, scanner, TransactionType.EXPENSE);
+                    break;
+                case "3":
+                    printTransactions(manager);
+                    break;
+                case "4":
+                    manager.printSummary();
+                    break;
+                case "5":
+                    StorageUtil.saveTransactions(manager.getAllTransactions(), DATA_FILE);
+                    break;
+                case "0":
+                    running = false;
+                    StorageUtil.saveTransactions(manager.getAllTransactions(), DATA_FILE);
+                    break;
+                default:
+                    System.out.println("无效选择，请重新输入。");
+            }
+        }
+
+        scanner.close();
+        System.out.println("谢谢使用记账系统，已退出。");
+    }
+
+    private static void printMenu() {
+        System.out.println("\n===== 简易记账系统 =====");
+        System.out.println("1. 记录收入");
+        System.out.println("2. 记录支出");
+        System.out.println("3. 查看全部记录");
+        System.out.println("4. 查看统计信息");
+        System.out.println("5. 手动保存数据");
+        System.out.println("0. 退出程序");
+        System.out.println("=======================");
+    }
+
+    private static void addTransaction(BudgetManager manager, Scanner scanner, TransactionType type) {
+        System.out.print("请输入金额：");
+        String amountInput = scanner.nextLine().trim();
+        double amount;
+        try {
+            amount = Double.parseDouble(amountInput);
+        } catch (NumberFormatException e) {
+            System.out.println("金额格式不正确，请重新输入。");
+            return;
+        }
+
+        if (amount <= 0) {
+            System.out.println("金额必须大于0。");
+            return;
+        }
+
+        System.out.print("请输入描述：");
+        String description = scanner.nextLine().trim();
+        if (description.isEmpty()) {
+            description = type == TransactionType.INCOME ? "收入" : "支出";
+        }
+
+        Transaction transaction = new Transaction(amount, type, description);
+        manager.addTransaction(transaction);
+        System.out.println("成功添加记录：" + transaction.format());
+    }
+
+    private static void printTransactions(BudgetManager manager) {
+        System.out.println("\n===== 当前记录 =====");
+        if (manager.getAllTransactions().isEmpty()) {
+            System.out.println("暂无记录。");
+        } else {
+            manager.getAllTransactions().forEach(t -> System.out.println(t.format()));
+        }
+    }
+}

SimpleBudgetTracker/src/com/example/budget/StorageUtil.java

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+package com.example.budget;
+
+import java.io.BufferedReader;
+import java.io.BufferedWriter;
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.List;
+
+public class StorageUtil {
+    public static void saveTransactions(List<Transaction> transactions, String filePath) {
+        try (BufferedWriter writer = Files.newBufferedWriter(Path.of(filePath))) {
+            for (Transaction t : transactions) {
+                writer.write(t.toFileFormat());
+                writer.newLine();
+            }
+            System.out.println("记录已成功保存到 " + filePath);
+        } catch (IOException e) {
+            System.err.println("保存记录失败: " + e.getMessage());
+        }
+    }
+
+    public static void loadTransactions(BudgetManager manager, String filePath) {
+        Path path = Path.of(filePath);
+        if (!Files.exists(path)) {
+            System.out.println("未找到交易记录文件，将创建新文件。");
+            return;
+        }
+        try (BufferedReader reader = Files.newBufferedReader(path)) {
+            String line;
+            while ((line = reader.readLine()) != null) {
+                try {
+                    Transaction transaction = Transaction.fromFileFormat(line);
+                    manager.addTransaction(transaction);
+                } catch (IllegalArgumentException ex) {
+                    System.err.println("跳过无效记录: " + line);
+                }
+            }
+            System.out.println("已从文件加载记录。");
+        } catch (IOException e) {
+            System.err.println("加载记录失败: " + e.getMessage());
+        }
+    }
+}

SimpleBudgetTracker/src/com/example/budget/Transaction.java

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+package com.example.budget;
+
+import java.time.LocalDateTime;
+import java.time.format.DateTimeFormatter;
+
+public class Transaction {
+    private final double amount;
+    private final TransactionType type;
+    private final String description;
+    private final LocalDateTime timestamp;
+
+    public Transaction(double amount, TransactionType type, String description) {
+        this.amount = amount;
+        this.type = type;
+        this.description = description;
+        this.timestamp = LocalDateTime.now();
+    }
+
+    public Transaction(double amount, TransactionType type, String description, LocalDateTime timestamp) {
+        this.amount = amount;
+        this.type = type;
+        this.description = description;
+        this.timestamp = timestamp;
+    }
+
+    public double getAmount() {
+        return amount;
+    }
+
+    public TransactionType getType() {
+        return type;
+    }
+
+    public String getDescription() {
+        return description;
+    }
+
+    public LocalDateTime getTimestamp() {
+        return timestamp;
+    }
+
+    public String format() {
+        DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
+        return String.format("%s | %s | %.2f | %s",
+                formatter.format(timestamp), type, amount, description);
+    }
+
+    public String toFileFormat() {
+        DateTimeFormatter formatter = DateTimeFormatter.ISO_LOCAL_DATE_TIME;
+        return String.format("%s|%s|%.2f|%s",
+                formatter.format(timestamp), type, amount, description.replace("|", "/"));
+    }
+
+    public static Transaction fromFileFormat(String line) {
+        String[] parts = line.split("\\|");
+        if (parts.length < 4) {
+            throw new IllegalArgumentException("Invalid line: " + line);
+        }
+        LocalDateTime time = LocalDateTime.parse(parts[0]);
+        TransactionType type = TransactionType.valueOf(parts[1]);
+        double amount = Double.parseDouble(parts[2]);
+        String description = parts[3];
+        return new Transaction(amount, type, description, time);
+    }
+}

SimpleBudgetTracker/src/com/example/budget/TransactionType.java

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+package com.example.budget;
+
+public enum TransactionType {
+    INCOME,
+    EXPENSE
+}