alex-ber

public static Method findMethod(Class<?> clazz, String name, Class<?>[] paramTypes) {
		Class<?> searchType = clazz;
		while (searchType != null) {
			Method[] methods = clazz.getDeclaredMethods();
			for (Method method : methods) {
				if (name.equals(method.getName()) && 
                                    (paramTypes == null || Arrays.equals(paramTypes, method.getParameterTypes()))) {
					return method;
				}
			}

alex-ber

interface I {
	public void f();
}
 
class A implements I {
	public void f() { System.out.println("A: doing f()"); }
}
 
class B implements I {
	public void f() { System.out.println("B: doing f()"); }

alex-ber

// changing the implementing object in run-time (normally done in compile time) 
class C implements I {
	private I i;
	// forwarding
	public C(I i){ this.i = i; }
	public void f() { i.f(); }
	
}
 

alex-ber

public class Main {
	public static void main(String[] arguments) {
		C c = new C(new A());
		c.f();	// output: A: doing f()
                c = new C(new B());
		c.f();	// output: B: doing f()

	}
}

alex-ber

Integer one = Integer.valueOf(1);
Integer[] ones = new Integer[]{one,one,one,one};  
Integer[] anotherOnes = ones;
Number[] numberOnes = ones;
	
//Integer[] illegalOnes=new Integer[]{"1","1","1","1"};
	
String str ="one";
String[] strs =new String[]{str};
String[] anotherStrs =strs;

alex-ber

public static Method findMethod(Class<?> clazz, String name, @Nullable Class<?>... paramTypes) {
		Class<?> searchType = clazz;
		while (searchType != null) {
			Method[] methods = clazz.getDeclaredMethods();
			for (Method method : methods) {
				if (name.equals(method.getName()) &&
						(paramTypes == null || Arrays.equals(paramTypes, method.getParameterTypes()))) {
					return method;
				}
			}

alex-ber

class Driver {
}

class Vehicle {
  private Driver driver;

  public Vehicle withDriver(Driver driver)
     this.driver = driver;
     return this;
  }

alex-ber

class SomeService {
   public int calcNumberOfWheels(Car[] cars){
     int length = (cars==null)?0:cars.
     if(length==0){
       return 0;
     }
		    
     long sum = 0L;
     int cur = 0;
     Car car = null;

alex-ber

Car[] cars={new Car(), new Car(), new SportCar()};
Object[] arr=cars; //arrays are covariant, it is legal assignment
arr[0]=new Motorcycle();    //as far as compiler concerns, it is legal, but this will crash at runtime with ArrayStoreException

alex-ber

Car[] cars={new Car(), new Car(), new SportCar()};
Object[] arr=cars; //arrays are covariant, it is legal assignment
arr[0]=new Motorcycle();    //as far as compiler concernt, it is legal, we're assiming no-runtime check
System.out.println(cars[0] instanceof Car);   //false, WTF?
cars[0].someCarMethod(); //crash at runtime