Explain the concept of proxy and in which scenarios it is used

A proxy is a surrogate object that controls access to another object. It implements the same interface as the original object and can add additional behavior when calling methods.

Use cases for proxies:

• Lazy loading: the object is created only upon first access.
• Access control: checking user permissions before method invocation.
• Logging and monitoring calls.
• Caching results.
• Transaction management.

For example, in Java, dynamic proxies can be used to add logging:

InvocationHandler handler = (proxy, method, args) -> {
    System.out.println("Method call: " + method.getName());
    return method.invoke(realObject, args);
};

MyInterface proxyInstance = (MyInterface) Proxy.newProxyInstance(
    realObject.getClass().getClassLoader(),
    realObject.getClass().getInterfaces(),
    handler
);

Thus, proxies allow flexible extension of object behavior without changing their code.