Section 13.5 Check Point Questions5 questions

13.5.1

Suppose A is an interface. Can you create an instance using new A()?

13.5.2

Suppose A is an interface. Can you declare a reference variable x with type A like this?

A x;

13.5.3

Which of the following is a correct interface?

(a)
interface A {    
  void print() { }
} 

(b)      
abstract interface A {    
  abstract void print() { }
}

(c)            
abstract interface A {    
  print();
} 

(d)        
interface A {   
  void print();
}

(e)
interface A {    
  default void print() {
  }
} 

(f)
interface A {    
  static int get() {
    return 0;
  }
}

13.5.4

Show the error in the following code:

interface A {
  void m1();
}

class B implements A {
  void m1() {
    System.out.println("m1");
  }
}

13.5.5

The following questions are based on the Edible interface and the classes defined in LiveExample 13.7 and also assume LittleChicken is a subtype of Chicken. For each question, answer if the code can compile, can run. If not, give a reason. If it runs, give the output.

a. Edible x = new Tiger(); 

b. Edible x = new Chicken(); 
   System.out.println(x.sound()); 
	
c. Edible x = new Chicken();
   System.out.println((Animal)x.sound());	

d. Edible x = new Chicken();
   System.out.println(((Animal)x).sound());
	
e. Edible x = new LittleChicken();
   System.out.println(x.howToEat());

f. LittleChicken x = new Chicken();