Interface implementation

[Tuna Töre]

Questions is taken from SCJP Exam for J2SE 5 from Paul Sanghera


Consider the following source file:
1. interface Animal {
2. void saySomething();
3. }
4. class farm {
5. void setName(String name){};
6. }
7. // insert code here
8. public class Cow implements Pasture {
9. public void graze() { }
10. void saySomething(){}
11.}
Which of the following code lines inserted independently at line 7 will make this source file compile?
A. interface Pasture {void graze();}
B. interface Pasture {void graze(){}}
C. interface Pasture extends Animal{void graze();}
D. interface Pasture extends Animal{void saySomething(){}}
E. interface Pasture implements Animal{void graze();}



I thought the answer is only A but the answer sheet says that A and C.

But, I thought that if we make saySomething default access in the subclass it is not allowed am I wrong because interface methods are public ?

we cannot convert public to default access, is it a typo like that ?
what do you think ?

[Ankit Garg]

yep, you are right...

[Tuna Töre]

[Bharath Raghavendra]

Hey Anut ,

The answers are A and C. If you observe the interface method 'saySomething' is never public in Animal.

And C is also an answer because Pasture is inheriting from 'saySomething' from Animal and adding a new method 'graze' to implement.And cow is implementing the both methods . Making graze() public is always allowed , as the access modifier of the method that is being implemented in the concrete class should same or less restrictive.

[Tuna Töre]

But interface methods are implicitly public so, you can't override it with default access (more restrictive), otherwise it gives error
Correct example should be like that
with public modifier.


interface Animal {
void saySomething();
}

class farm {
void setName(String name) {
};
}

interface Pasture extends Animal {
void graze();
}

public class Cow implements Pasture {
public void graze() {
}

public void saySomething() {
}
}

[Vipul Prajapati]

According to the question the answer would be A only.
Try to compile this code it'll give an error of "Cannot reduce the visibilty of the inherited method".
[ October 20, 2008: Message edited by: Vipul Prajapati ]