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Java学习记录
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| /** | |
| * 冒泡排序 | |
| */ | |
| static class BubbleSort { | |
| public static void main(String[] args) { | |
| int[] arr = new int[]{1, 3, 5, 0, 7, -8, 4, 1, 8, 9, 12, 2}; | |
| for (int i = 0; i < arr.length - 1; i++) { | |
| for (int j = 0; j < arr.length - 1 - i; j++) { | |
| if (arr[j] > arr[j + 1]) { | |
| // 如果左侧的比右侧的大，那么交换 | |
| arr[j] ^= arr[j + 1]; | |
| arr[j + 1] ^= arr[j]; | |
| arr[j] ^= arr[j + 1]; | |
| } | |
| } | |
| } | |
| System.out.println(Arrays.toString(arr)); | |
| } | |
| } |
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| /** | |
| * 写一个方法，输入一个文件名和一个字符串，统计这个字符串在这个文件中出现的次数 | |
| * | |
| * @param fileName | |
| * @param word | |
| * @return | |
| * @throws IOException | |
| */ | |
| long countWordInFile(String fileName, String word) throws IOException { | |
| long counter = 0; | |
| try (FileReader reader = new FileReader(fileName)) { | |
| try (BufferedReader bufferedReader = new BufferedReader(reader)) { | |
| String line; | |
| while ((line = bufferedReader.readLine()) != null) { | |
| if (line.length() > word.length() && line.contains(word)) { | |
| counter++; | |
| } | |
| } | |
| } | |
| } | |
| return counter; | |
| } |
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| /** | |
| * 编程实现文件拷贝 | |
| * | |
| * @param source | |
| * @param target | |
| * @throws IOException | |
| */ | |
| void fileCopy(String source, String target) throws IOException { | |
| try (InputStream inputStream = new FileInputStream(source)) { | |
| try (OutputStream outputStream = new FileOutputStream(target)) { | |
| byte[] buf = new byte[1024]; | |
| int bufToRead; | |
| while ((bufToRead = inputStream.read(buf)) != -1) { | |
| outputStream.write(buf, 0, bufToRead); | |
| } | |
| } | |
| } | |
| } | |
| /** | |
| * 编程实现文件拷贝 | |
| * | |
| * @param source | |
| * @param target | |
| * @throws IOException | |
| */ | |
| void fileCopyNIO(String source, String target) throws IOException { | |
| try (FileInputStream in = new FileInputStream(source)) { | |
| try (FileOutputStream out = new FileOutputStream(target)) { | |
| FileChannel inFileChannel = in.getChannel(); | |
| FileChannel outFileChannel = out.getChannel(); | |
| ByteBuffer byteBuffer = ByteBuffer.allocate(1024); | |
| while (inFileChannel.read(byteBuffer) != -1) { | |
| byteBuffer.flip(); | |
| outFileChannel.write(byteBuffer); | |
| byteBuffer.clear(); | |
| } | |
| } | |
| } | |
| } |
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| /** | |
| * JDBC 的连接案例 | |
| * | |
| * @throws ClassNotFoundException | |
| */ | |
| void jdbcDemo() throws ClassNotFoundException { | |
| // 加载驱动 | |
| Class.forName("com.mysql.cj.jdbc.Driver"); | |
| // 建立连接 | |
| try (Connection connection = DriverManager.getConnection("")) { | |
| // 构造语句对象 | |
| PreparedStatement ps = connection.prepareStatement("select * from demo where id > ? and id < ?"); | |
| ps.setInt(1, 23); | |
| ps.setInt(2, 10); | |
| // 事务处理 | |
| // connection.setAutoCommit(false); | |
| ResultSet resultSet = ps.executeQuery(); | |
| // connection.commit(); | |
| // connection.rollback(); | |
| while (resultSet.next()) { | |
| System.out.println(resultSet.getString("name")); | |
| } | |
| } catch (SQLException e) { | |
| e.printStackTrace(); | |
| } | |
| } |
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| /** | |
| * 双重校验锁实现单例模式 | |
| */ | |
| static class Singleton { | |
| private static volatile Singleton singleton = null; | |
| private Singleton() { | |
| } | |
| public static Singleton getInstance() { | |
| // 第一次校验，这里不加锁，毕竟只有第一次是 null，其他情况无需上锁 | |
| if (singleton == null) { | |
| // 先上锁，确保只放进来一个进程 | |
| synchronized (Singleton.class) { | |
| // 第二次校验，这里只有一个进程能进来 | |
| if (singleton == null) { | |
| singleton = new Singleton(); | |
| } | |
| } | |
| } | |
| return singleton; | |
| } | |
| } |
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