interface A {void f1(); void f2();}

interface B {void f3(); void f4();}

class C implements A {
	public void f1() {} 
	public void f2() {}
}

class D implements A,B {
	public void f1() {} 
	public void f2() {}
	public void f3() {} 
	public void f4() {}
}

abstract class C2 implements A {
	public void f1() {} 
}


//=================

interface A2 {void f1(); void f5();}

class X implements A, A2  {
	public void f1() {}	
	public void f2() {}	
	public void f5() {}	
}

//=================

interface T extends A,B {
	public void f5();
}

class D2 extends D implements T {
	public void f5() {}
}

// class Employee extends Person implements I1, I2 
// {
//	..
// }

//=================

public class Main
{
	public static void main(String[] args) 
	{
		A a;
		B b;
		C c;
		D d;
		C2 c2;
		//a = new A(); //Cannot instantiate the type A
		//b = new B(); //Cannot instantiate the type B
		c = new C();
		d = new D();
		//x5 = new C2(); // Cannot instantiate the type C2
	
		a = c;
		b = d;
		c = (C)a;
		d = (D)b;
		
		T t;
		t = (T)a;
		a = t;
	}
}