ProtectionProxy.java

// Protection Proxy

package structural.proxy;

interface Drivable
{
    void drive();
}

class Car implements Drivable
{
    protected Driver driver;

    public Car(Driver driver) {
        this.driver = driver;
    }

    @Override
    public void drive() {
        System.out.println("Car being driven");
    }
}

class Driver
{
    public int age;

    public Driver(int age) {
        this.age = age;
    }
}

// Proxy to make some checks on driver age - using inheritance
class CarProxy extends Car {
    public CarProxy(Driver driver) {
        super(driver);
    }

    @Override
    public void drive() {
        if(driver.age >= 16)
            super.drive();
        else
            System.out.println("Driver too young!");
    }
}

class ProtectionProxyDemo
{
    public static void main(String[] args) {
        Car car = new Car(new Driver(12));
        car.drive(); // no age checks made

        Car car2 = new CarProxy(new Driver(12)); // proxy used here
        car2.drive();
    }
}