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);
}
}