import java.util.ArrayList; import java.util.List; public class CollectionExample { public static void main(String[] args) { List<String> list = new ArrayList<>(); list.add("Hello"); list.add("World"); for (String str : list) { System.out.println(str); } } } import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; public class ConcurrencyExample { public static void main(String[] args) { ExecutorService executor = Executors.newFixedThreadPool(5); for (int i = 0; i < 10; i++) { Runnable worker = new WorkerThread("" + i); executor.execute(worker); } executor.shutdown(); while (!executor.isTerminated()) { } System.out.println("Finished all threads"); } } class WorkerThread implements Runnable { private String message; public WorkerThread(String message) { this.message = message; } public void run() { System.out.println(Thread.currentThread().getName() + " (Start) message = " + message); processMessage(); System.out.println(Thread.currentThread().getName() + " (End)"); } private void processMessage() { try { Thread.sleep(2000); } catch (InterruptedException e) { e.printStackTrace(); } } } import java.io.BufferedReader; import java.io.FileReader; import java.io.FileWriter; import java.io.IOException; public class IOExample { public static void main(String[] args) { try { FileWriter writer = new FileWriter("output.txt"); writer.write("Hello World"); writer.close(); BufferedReader reader = new BufferedReader(new FileReader("output.txt")); String line = reader.readLine(); System.out.println(line); reader.close(); } catch (IOException e) { e.printStackTrace(); } } } import java.lang.reflect.Constructor; import java.lang.reflect.Method; public class ReflectionExample { public static void main(String[] args) { try { Class<?> cls = Class.forName("MyClass"); Method method = cls.getDeclaredMethod("myMethod"); method.invoke(cls.newInstance()); Constructor<?> constructor = cls.getDeclaredConstructor(String.class); constructor.setAccessible(true); Object obj = constructor.newInstance("Hello"); method.invoke(obj); } catch (Exception e) { e.printStackTrace(); } } } class MyClass { private String message; public MyClass() { this.message = "Default"; } private MyClass(String message) { this.message = message; } public void myMethod() { System.out.println("Message: " + message); } }


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