50个JAVA常见代码大全

fangxinyzj.com 2025-05-30 09:51:44

引言

Java 是一种广泛使用的编程语言，适用于多种应用场景，从企业级应用到移动应用开发。掌握一些常见的 Java 代码片段可以帮助开发者提高编码效率，解决常见问题。本文整理了50个常见的 Java 代码片段，涵盖了字符串处理、集合操作、文件操作、异常处理等多个方面，旨在为开发者提供实用的参考。

1. 字符串处理

  1. 字符串拼接

    String str1 = "Hello";
String str2 = "World";
String result = str1 + " " + str2;

  2. 字符串转大写

    String str = "hello";
String upperCase = str.toUpperCase();

  3. 字符串转小写

    String str = "HELLO";
String lowerCase = str.toLowerCase();

  4. 字符串截取

    String str = "Hello, World!";
String subStr = str.substring(0, 5);

  5. 字符串分割

    String str = "Hello,World,Java";
String[] parts = str.split(",");

  6. 字符串替换

    String str = "Hello, World!";
String replaced = str.replace("World", "Java");

  7. 字符串去空格

    String str = " Hello, World! ";
String trimmed = str.trim();

  8. 字符串长度

    String str = "Hello, World!";
int length = str.length();

  9. 字符串包含

    String str = "Hello, World!";
boolean contains = str.contains("World");

  10. 字符串比较

    String str1 = "Hello";
String str2 = "hello";
boolean equals = str1.equalsIgnoreCase(str2);
2. 集合操作

  1. 创建列表

    List list = new ArrayList<>();
list.add("Apple");
list.add("Banana");

  2. 遍历列表

    List list = Arrays.asList("Apple", "Banana", "Cherry");
for (String item : list) {
    System.out.println(item);
}

  3. 创建集合

    Set set = new HashSet<>();
set.add("Apple");
set.add("Banana");

  4. 遍历集合

    Set set = new HashSet<>(Arrays.asList("Apple", "Banana", "Cherry"));
for (String item : set) {
    System.out.println(item);
}

  5. 创建映射

    Map map = new HashMap<>();
map.put("Apple", 1);
map.put("Banana", 2);

  6. 遍历映射

    Map map = new HashMap<>();
map.put("Apple", 1);
map.put("Banana", 2);
for (Map.Entry entry : map.entrySet()) {
    System.out.println(entry.getKey() + ": " + entry.getValue());
}

  7. 集合排序

    List list = Arrays.asList("Cherry", "Apple", "Banana");
Collections.sort(list);

  8. 集合去重

    List list = Arrays.asList("Apple", "Banana", "Apple", "Cherry");
Set uniqueSet = new HashSet<>(list);

  9. 集合转数组

    List list = Arrays.asList("Apple", "Banana", "Cherry");
String[] array = list.toArray(new String[0]);

  10. 集合过滤

    List list = Arrays.asList("Apple", "Banana", "Cherry");
List filteredList = list.stream()
                                .filter(s -> s.startsWith("A"))
                                .collect(Collectors.toList());
3. 文件操作

  1. 读取文件

    Path path = Paths.get("file.txt");
List lines = Files.readAllLines(path);

  2. 写入文件

    Path path = Paths.get("file.txt");
List lines = Arrays.asList("Hello", "World");
Files.write(path, lines, StandardCharsets.UTF_8);

  3. 追加文件

    Path path = Paths.get("file.txt");
List lines = Arrays.asList("Hello", "World");
Files.write(path, lines, StandardCharsets.UTF_8, StandardOpenOption.APPEND);

  4. 删除文件

    Path path = Paths.get("file.txt");
Files.delete(path);

  5. 创建目录

    Path path = Paths.get("newDir");
Files.createDirectories(path);

  6. 遍历目录

    Path path = Paths.get("dir");
Files.walk(path)
     .forEach(System.out::println);

  7. 复制文件

    Path source = Paths.get("source.txt");
Path target = Paths.get("target.txt");
Files.copy(source, target, StandardCopyOption.REPLACE_EXISTING);

  8. 移动文件

    Path source = Paths.get("source.txt");
Path target = Paths.get("target.txt");
Files.move(source, target, StandardCopyOption.REPLACE_EXISTING);

  9. 检查文件是否存在

    Path path = Paths.get("file.txt");
boolean exists = Files.exists(path);

  10. 获取文件大小

    Path path = Paths.get("file.txt");
long size = Files.size(path);
4. 异常处理

  1. 捕获异常

    try {
    int result = 10 / 0;
} catch (ArithmeticException e) {
    System.out.println("Division by zero error");
}

  2. 抛出异常

    public void divide(int a, int b) throws ArithmeticException {
    if (b == 0) {
        throw new ArithmeticException("Division by zero");
    }
    return a / b;
}

  3. 自定义异常

    public class CustomException extends Exception {
    public CustomException(String message) {
        super(message);
    }
}

  4. 多重捕获

    try {
    // Some code that may throw exceptions
} catch (IOException | SQLException e) {
    System.out.println("Caught exception: " + e.getMessage());
}

  5. finally块

    try {
    // Some code that may throw exceptions
} catch (IOException e) {
    System.out.println("Caught exception: " + e.getMessage());
} finally {
    System.out.println("Finally block executed");
}

  6. try-with-resources

    try (BufferedReader reader = new BufferedReader(new FileReader("file.txt"))) {
    String line;
    while ((line = reader.readLine()) != null) {
        System.out.println(line);
    }
} catch (IOException e) {
    System.out.println("Error reading file: " + e.getMessage());
}
5. 线程与并发

  1. 创建线程

    Thread thread = new Thread(() -> {
    System.out.println("Thread is running");
});
thread.start();

  2. 同步方法

    public synchronized void synchronizedMethod() {
    // Synchronized code
}

  3. 同步块

    Object lock = new Object();
synchronized (lock) {
    // Synchronized code
}

  4. 等待和通知

    Object lock = new Object();
synchronized (lock) {
    try {
        lock.wait();
    } catch (InterruptedException e) {
        e.printStackTrace();
    }
}
synchronized (lock) {
    lock.notify();
}

  5. 线程池

    ExecutorService executor = Executors.newFixedThreadPool(5);
for (int i = 0; i < 10; i++) {
    executor.submit(() -> {
        System.out.println("Task executed by " + Thread.currentThread().getName());
    });
}
executor.shutdown();

  6. Future和Callable

    ExecutorService executor = Executors.newSingleThreadExecutor();
Future future = executor.submit(() -> {
    return 10;
});
try {
    int result = future.get();
    System.out.println("Result: " + result);
} catch (InterruptedException | ExecutionException e) {
    e.printStackTrace();
}
executor.shutdown();

  7. CountDownLatch

    CountDownLatch latch = new CountDownLatch(3);
for (int i = 0; i < 3; i++) {
    new Thread(() -> {
        System.out.println("Thread " + Thread.currentThread().getName() + " is running");
        latch.countDown();
    }).start();
}
latch.await();
System.out.println("All threads have finished");

  8. CyclicBarrier

    CyclicBarrier barrier = new CyclicBarrier(3, () -> {
    System.out.println("All parties have arrived at the barrier");
});
for (int i = 0; i < 3; i++) {
    new Thread(() -> {
        System.out.println("Thread " + Thread.currentThread().getName() + " is waiting");
        try {
            barrier.await();
        } catch (InterruptedException | BrokenBarrierException e) {
            e.printStackTrace();
        }
    }).start();
}

  9. Semaphore

    Semaphore semaphore = new Semaphore(3);
for (int i = 0; i < 5; i++) {
    new Thread(() -> {
        try {
            semaphore.acquire();
            System.out.println("Thread " + Thread.currentThread().getName() + " acquired permit");
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            semaphore.release();
            System.out.println("Thread " + Thread.currentThread().getName() + " released permit");
        }
    }).start();
}
6. 其他常用代码

  1. 日期和时间

    LocalDate date = LocalDate.now();
LocalTime time = LocalTime.now();
LocalDateTime dateTime = LocalDateTime.now();

  2. 格式化日期

    DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
String formattedDate = LocalDateTime.now().format(formatter);

  3. 解析日期

    DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
LocalDateTime dateTime = LocalDateTime.parse("2023-10-01 12:30:00", formatter);

  4. 随机数生成

    Random random = new Random();
int randomNumber = random.nextInt(100);

  5. JSON处理

    JSONObject jsonObject = new JSONObject();
jsonObject.put("name", "John");
jsonObject.put("age", 30);
String jsonString = jsonObject.toString();
总结

以上是50个常见的 Java 代码片段，涵盖了字符串处理、集合操作、文件操作、异常处理、线程与并发以及其他常用操作。这些代码片段可以帮助开发者快速解决常见问题，提高开发效率。

上一篇：cpu怎么设置最佳性能（如何让CPU能发挥系统最大性能）
下一篇：windows7u盘重装系统（如何用u盘重装系统win7）
Copyright © 2007-2024 翔大跳伞俱乐部 版权所有 豫ICP备11006092号-1 XML