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Java核心API实战：从字符串到多线程全解析

ops 2025/8/21 17:07:38

Java常用API详解与代码实践

一、字符串处理类

1. String类

// 字符串基础操作
String str = "Hello,Java!";
System.out.println(str.substring(7)); // 输出"Java!"
System.out.println(str.indexOf("Java")); // 输出7// 正则表达式匹配
String email = "test@example.com";
System.out.println(email.matches("^\\w+@[a-zA-Z_]+?\\.[a-zA-Z]{2,3}$")); // true

2. StringBuilder/StringBuffer

// 字符串拼接性能优化
StringBuilder sb = new StringBuilder();
sb.append("Java").append(17).insert(0, "Version: ");
System.out.println(sb.toString()); // 输出"Version: Java17"

二、集合框架

1. List接口

// ArrayList示例
List<String> list = new ArrayList<>();
list.add("Apple");
list.add(0, "Banana");
System.out.println(list.get(1)); // 输出"Apple"// LinkedList特殊操作
LinkedList<Integer> linkedList = new LinkedList<>();
linkedList.addFirst(10);
linkedList.pollLast();

2. Map接口

// HashMap使用
Map<String, Integer> map = new HashMap<>();
map.put("Java", 1995);
map.computeIfAbsent("Python", k -> 1991);// TreeMap排序
TreeMap<Integer, String> treeMap = new TreeMap<>(Comparator.reverseOrder());
treeMap.put(3, "Three");
treeMap.put(1, "One");
System.out.println(treeMap.firstKey()); // 输出3

三、IO流体系

1. 文件操作

// 使用NIO读取文件
Path path = Paths.get("test.txt");
try (Stream<String> lines = Files.lines(path)) {lines.filter(line -> line.contains("Java")).forEach(System.out::println);
}// 缓冲流复制文件
try (BufferedReader reader = new BufferedReader(new FileReader("input.txt"));BufferedWriter writer = new BufferedWriter(new FileWriter("output.txt"))) {String line;while ((line = reader.readLine()) != null) {writer.write(line.toUpperCase());writer.newLine();}
}

四、日期时间API（Java 8+）

1. 基础日期操作

LocalDate today = LocalDate.now();
LocalDate nextWeek = today.plusWeeks(1);
System.out.println(today.isBefore(nextWeek)); // true// 日期格式化
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy/MM/dd");
System.out.println(today.format(formatter));

2. 时间差计算

LocalDateTime start = LocalDateTime.of(2023, 1, 1, 9, 0);
LocalDateTime end = LocalDateTime.now();Duration duration = Duration.between(start, end);
System.out.println(duration.toDays() + " days");

五、多线程编程

1. 线程基础

// 实现Runnable接口
new Thread(() -> {IntStream.range(1, 5).forEach(i -> {System.out.println("Task-" + i);try { Thread.sleep(500); } catch (InterruptedException e) {}});
}).start();

2. 线程池管理

ExecutorService executor = Executors.newFixedThreadPool(3);
executor.submit(() -> System.out.println("Task1"));
executor.submit(() -> System.out.println("Task2"));
executor.shutdown();

六、异常处理机制

1. 自定义异常

class BalanceException extends Exception {public BalanceException(String message) {super(message);}
}void withdraw(double amount) throws BalanceException {if (amount > balance) {throw new BalanceException("余额不足");}// 扣款逻辑
}

七、反射机制

1. 动态调用方法

Class<?> clazz = Class.forName("com.example.User");
Object user = clazz.getDeclaredConstructor().newInstance();Method setName = clazz.getMethod("setName", String.class);
setName.invoke(user, "张三");Field ageField = clazz.getDeclaredField("age");
ageField.setAccessible(true);
ageField.set(user, 25);