public class CollectionsExample {
public static void main(String[] args) {
// List – 有序，可重复
List list = new ArrayList<>();
list.add(“Apple”);
list.add(“Banana”);
list.add(“Orange”);
list.add(“Apple”); // 允许重复

System.out.println(“List:”);
for (String fruit : list) {
System.out.println(fruit);
}

// Set – 无序，不可重复
Set set = new HashSet<>();
set.add(“Apple”);
set.add(“Banana”);
set.add(“Orange”);
set.add(“Apple”); // 重复元素不会被添加

System.out.println(“\nSet:”);
for (String fruit : set) {
System.out.println(fruit);
}

// Map – 键值对
Map map = new HashMap<>();
map.put(“Apple”, 100);
map.put(“Banana”, 50);
map.put(“Orange”, 75);

System.out.println(“\nMap:”);
for (Map.Entry entry : map.entrySet()) {
System.out.println(entry.getKey() + “: ” + entry.getValue());
}

// 集合操作
System.out.println(“\nList size: ” + list.size());
System.out.println(“Set contains ‘Apple’: ” + set.contains(“Apple”));
System.out.println(“Map get ‘Banana’: ” + map.get(“Banana”));

// 排序
Collections.sort(list);
System.out.println(“\nSorted List:”);
for (String fruit : list) {
System.out.println(fruit);
}
}
}

// 输出:
// List:
// Apple
// Banana
// Orange
// Apple
//
// Set:
// Apple
// Banana
// Orange
//
// Map:
// Apple: 100
// Banana: 50
// Orange: 75
//
// List size: 4
// Set contains ‘Apple’: true
// Map get ‘Banana’: 50
//
// Sorted List:
// Apple
// Apple
// Banana
// Orange

public class ExceptionExample {
public static void main(String[] args) {
// try-catch-finally
try {
int result = divide(10, 0);
System.out.println(“Result: ” + result);
} catch (ArithmeticException e) {
System.out.println(“Error: ” + e.getMessage());
} finally {
System.out.println(“Finally block executed”);
}

// 多个catch块
try {
String str = null;
System.out.println(str.length());
} catch (ArithmeticException e) {
System.out.println(“Arithmetic error: ” + e.getMessage());
} catch (NullPointerException e) {
System.out.println(“Null pointer error: ” + e.getMessage());
} catch (Exception e) {
System.out.println(“General error: ” + e.getMessage());
}

// 抛出异常
try {
checkAge(-5);
} catch (IllegalArgumentException e) {
System.out.println(“Error: ” + e.getMessage());
}

// 自定义异常
try {
validateEmail(“invalid-email”);
} catch (EmailValidationException e) {
System.out.println(“Email validation error: ” + e.getMessage());
}
}

// 可能抛出异常的方法
public static int divide(int a, int b) {
return a / b;
}

// 抛出异常的方法
public static void checkAge(int age) {
if (age < 0) { throw new IllegalArgumentException("Age cannot be negative"); } System.out.println("Valid age: " + age); } // 抛出自定义异常的方法 public static void validateEmail(String email) throws EmailValidationException { if (!email.contains("@")) { throw new EmailValidationException("Invalid email format"); } System.out.println("Valid email: " + email); } } // 自定义异常类 class EmailValidationException extends Exception { public EmailValidationException(String message) { super(message); } } // 输出: // Error: / by zero // Finally block executed // Null pointer error: Cannot invoke "String.length()" because "str" is null // Error: Age cannot be negative // Email validation error: Invalid email format

public class IOExample {
public static void main(String[] args) {
// 写入文件
try (FileWriter writer = new FileWriter(“example.txt”)) {
writer.write(“Hello, Java I/O!\n”);
writer.write(“This is a test file.\n”);
System.out.println(“File written successfully”);
} catch (IOException e) {
e.printStackTrace();
}

// 读取文件
try (FileReader reader = new FileReader(“example.txt”)) {
int character;
System.out.println(“File content:”);
while ((character = reader.read()) != -1) {
System.out.print((char) character);
}
} catch (IOException e) {
e.printStackTrace();
}

// 使用BufferedReader
try (BufferedReader br = new BufferedReader(new FileReader(“example.txt”))) {
String line;
System.out.println(“\nUsing BufferedReader:”);
while ((line = br.readLine()) != null) {
System.out.println(line);
}
} catch (IOException e) {
e.printStackTrace();
}

// 使用NIO Paths和Files
try {
Path path = Paths.get(“example.txt”);
System.out.println(“\nUsing NIO:”);
Files.lines(path).forEach(System.out::println);
} catch (IOException e) {
e.printStackTrace();
}
}
}

// 输出:
// File written successfully
// File content:
// Hello, Java I/O!
// This is a test file.
//
// Using BufferedReader:
// Hello, Java I/O!
// This is a test file.
//
// Using NIO:
// Hello, Java I/O!
// This is a test file.

// 方式1：继承Thread类
class MyThread extends Thread {
private String name;

public MyThread(String name) {
this.name = name;
}

@Override
public void run() {
for (int i = 1; i <= 5; i++) { System.out.println(name + ": " + i); try { Thread.sleep(500); // 暂停500毫秒 } catch (InterruptedException e) { e.printStackTrace(); } } } } // 方式2：实现Runnable接口 class MyRunnable implements Runnable { private String name; public MyRunnable(String name) { this.name = name; } @Override public void run() { for (int i = 1; i <= 5; i++) { System.out.println(name + ": " + i); try { Thread.sleep(500); } catch (InterruptedException e) { e.printStackTrace(); } } } } public class MultithreadingExample { public static void main(String[] args) { // 使用Thread类 MyThread thread1 = new MyThread("Thread 1"); MyThread thread2 = new MyThread("Thread 2"); thread1.start(); thread2.start(); // 使用Runnable接口 Thread thread3 = new Thread(new MyRunnable("Thread 3")); Thread thread4 = new Thread(new MyRunnable("Thread 4")); thread3.start(); thread4.start(); // 使用Lambda表达式（Java 8+） Thread thread5 = new Thread(() -> {
for (int i = 1; i <= 5; i++) { System.out.println("Thread 5: " + i); try { Thread.sleep(500); } catch (InterruptedException e) { e.printStackTrace(); } } }); thread5.start(); } } // 输出（顺序可能不同）: // Thread 1: 1 // Thread 2: 1 // Thread 3: 1 // Thread 4: 1 // Thread 5: 1 // Thread 1: 2 // Thread 2: 2 // Thread 3: 2 // Thread 4: 2 // Thread 5: 2 // Thread 1: 3 // Thread 2: 3 // Thread 3: 3 // Thread 4: 3 // Thread 5: 3 // Thread 1: 4 // Thread 2: 4 // Thread 3: 4 // Thread 4: 4 // Thread 5: 4 // Thread 1: 5 // Thread 2: 5 // Thread 3: 5 // Thread 4: 5 // Thread 5: 5

public class LambdaStreamExample {
public static void main(String[] args) {
// 列表
List fruits = Arrays.asList(“Apple”, “Banana”, “Orange”, “Mango”, “Pineapple”);

// 使用Lambda表达式
System.out.println(“Using Lambda expressions:”);

// 遍历列表
fruits.forEach(fruit -> System.out.println(fruit));

// 使用Stream API
System.out.println(“\nUsing Stream API:”);

// 过滤操作
System.out.println(“Fruits starting with ‘A’:”);
fruits.stream()
.filter(fruit -> fruit.startsWith(“A”))
.forEach(System.out::println);

// 映射操作
System.out.println(“\nFruit lengths:”);
fruits.stream()
.map(fruit -> fruit.length())
.forEach(System.out::println);

// 排序操作
System.out.println(“\nSorted fruits:”);
fruits.stream()
.sorted()
.forEach(System.out::println);

// 收集操作
System.out.println(“\nCollecting to list:”);
List sortedFruits = fruits.stream()
.sorted()
.collect(Collectors.toList());
System.out.println(sortedFruits);

// 聚合操作
System.out.println(“\nTotal fruit length:”);
int totalLength = fruits.stream()
.mapToInt(String::length)
.sum();
System.out.println(totalLength);

// 查找操作
System.out.println(“\nAny fruit starts with ‘P’:”);
boolean anyStartsWithP = fruits.stream()
.anyMatch(fruit -> fruit.startsWith(“P”));
System.out.println(anyStartsWithP);

System.out.println(“\nAll fruits have length > 3:”);
boolean allLengthGreaterThan3 = fruits.stream()
.allMatch(fruit -> fruit.length() > 3);
System.out.println(allLengthGreaterThan3);
}
}

// 输出:
// Using Lambda expressions:
// Apple
// Banana
// Orange
// Mango
// Pineapple
//
// Using Stream API:
// Fruits starting with ‘A’:
// Apple
//
// Fruit lengths:
// 5
// 6
// 6
// 5
// 9
//
// Sorted fruits:
// Apple
// Banana
// Mango
// Orange
// Pineapple
//
// Collecting to list:
// [Apple, Banana, Mango, Orange, Pineapple]
//
// Total fruit length:
// 31
//
// Any fruit starts with ‘P’:
// true
//
// All fruits have length > 3:
// true

# 1. 代码规范
– 遵循Oracle Java Code Conventions或Google Java Style Guide
– 使用有意义的变量和方法命名
– 保持代码缩进一致
– 编写清晰的注释
– 避免过长的方法和类

# 2. 性能优化
– 使用StringBuilder进行字符串拼接
– 避免在循环中创建对象
– 使用适当的集合类型
– 合理使用多线程
– 避免过度使用反射

# 3. 安全性
– 防止SQL注入
– 防止XSS攻击
– 使用HTTPS
– 合理处理异常
– 避免硬编码敏感信息

# 4. 测试
– 编写单元测试
– 使用JUnit或TestNG框架
– 实现集成测试
– 进行性能测试

# 5. 工具和框架
– 使用Maven或Gradle进行依赖管理
– 使用IDE（如IntelliJ IDEA、Eclipse）提高开发效率
– 使用版本控制工具（如Git）
– 考虑使用Spring Boot等框架加速开发