// Creating an instance of the String class
String myString = new String("Hello World!");// Getting the length of the string
int length = myString.length();// Concatenating two strings
String newString = "Hello" + " " + "World!";// Comparing two strings for equality
boolean isEqual = myString.equals("Hello World!");// Converting an integer to a string
String numberString = Integer.toString(123);// Parsing a string to an integer
int number = Integer.parseInt("123");// Formatting a string with placeholders
String formattedString = String.format("Name: %s, Age: %d", "John", 25);// Matching a pattern in a string
Pattern pattern = Pattern.compile("[a-zA-Z]+");
Matcher matcher = pattern.matcher("This is a test string");
// Checking if the pattern matches any part of the string
boolean matches = matcher.find();// Creating a thread
Thread thread = new Thread(() -> System.out.println("Hello from a thread!"));
// Starting the thread
thread.start();// Synchronizing a block of code to prevent race conditions
synchronized (myObject) {
// Code that should be executed in a thread-safe manner
}try {
// Code that may throw an exception
} catch (Exception e) {
// Code to handle the exception
}// Creating an ArrayList
ArrayList<String> names = new ArrayList<>();
// Adding elements to the list
names.add("John");
names.add("Mary");
// Getting an element from the list
String name = names.get(0);// Creating a HashSet
Set<Integer> numbers = new HashSet<>();
// Adding elements to the set
numbers.add(1);
numbers.add(2);
numbers.add(3);
// Checking if the set contains a certain element
boolean contains = numbers.contains(2);// Creating a HashMap
Map<String, Integer> ages = new HashMap<>();
// Putting a key-value pair into the map
ages.put("John", 25);
// Getting the value associated with a key
int age = ages.get("John");// Creating a stream
Stream<Integer> numbersStream = Stream.of(1, 2, 3, 4, 5);
// Performing operations on the stream
int sum = numbersStream.reduce(0, Integer::sum);// Creating a lambda expression
Runnable task = () -> System.out.println("Hello from a lambda!");
// Running the lambda
new Thread(task).start();// Creating a generic class
class MyContainer<T> {
private T value;
public T getValue() {
return value;
}
public void setValue(T value) {
this.value = value;
}
}
// Creating an instance of the generic class
MyContainer<String> container = new MyContainer<>();// Creating a superclass
class Animal {
public void eat() {
System.out.println("Animal is eating...");
}
}
// Creating a subclass
class Dog extends Animal {
@Override
public void eat() {
System.out.println("Dog is eating...");
}
}
// Creating an instance of the subclass
Dog dog = new Dog();
dog.eat();// Creating a superclass
class Shape {
public void draw() {
System.out.println("Shape is being drawn...");
}
}
// Creating a subclass
class Circle extends Shape {
@Override
public void draw() {
System.out.println("Circle is being drawn...");
}
}
// Using the superclass reference to call the overridden method
Shape shape = new Circle();
shape.draw();// Creating an interface
interface Flyable {
void fly();
}
// Creating a class that implements the interface
class Bird implements Flyable {
@Override
public void fly() {
System.out.println("Bird is flying...");
}
}
// Creating an instance of the class that implements the interface
Bird bird = new Bird();
bird.fly();// Creating an instance of the Class class
Class<?> clazz = Class.forName("java.lang.String");
// Getting information about the class
String name = clazz.getName();
Method[] methods = clazz.getMethods();// Creating an annotation
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface Loggable {
}
// Annotating a method
@Loggable
public void myMethod() {
// Implementation goes here
}// Creating a JAR file
JarFile jarFile = new JarFile("my-app.jar");// Creating a custom class loader
class MyClassLoader extends ClassLoader {
@Override
protected Class<?> findClass(String name) throws ClassNotFoundException {
// Implementation goes here
}
}
// Loading a class using the custom class loader
Class<?> clazz = new MyClassLoader().loadClass("MyClass");// Creating an object to be serialized
Person person = new Person("John", 25);
// Serializing the object
FileOutputStream fileOutputStream = new FileOutputStream("person.ser");
ObjectOutputStream objectOutputStream = new ObjectOutputStream(fileOutputStream);
objectOutputStream.writeObject(person);
// Deserializing the object
FileInputStream fileInputStream = new FileInputStream("person.ser");
ObjectInputStream objectInputStream = new ObjectInputStream(fileInputStream);
Person deserializedPerson = (Person) objectInputStream.readObject();// Creating a socket
Socket socket = new Socket("localhost", 8080);// Creating a server socket
ServerSocket serverSocket = new ServerSocket(8080);// Sending data to a socket
DataOutputStream dataOutputStream = new DataOutputStream(socket.getOutputStream());
dataOutputStream.writeUTF("Hello from client!");
// Receiving data from a socket
DataInputStream dataInputStream = new DataInputStream(socket.getInputStream());
String message = dataInputStream.readUTF();// Creating a URL object
URL url = new URL("https://example.com");// Creating an HTTP client
HttpClient httpClient = new HttpClient();
// Sending an HTTP request
HttpMethod method = new GetMethod("https://example.com");
HttpResponse response = httpClient.executeMethod(method);// Getting the current date and time
LocalDateTime now = LocalDateTime.now();// Formatting the date and time
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
String formattedDateTime = now.format(formatter);