Declarations and Access Control – Interview Questions & Answers

1. Which is true? (Choose all that apply.)
A. “X extends Y” is correct if and only if X is a class and Y is an interface
B. “X extends Y” is correct if and only if X is an interface and Y is a class
C. “X extends Y” is correct if X and Y are either both classes or both interfaces
D. “X extends Y” is correct for all combinations of X and Y being classes and/or interfaces

Answer:
® ✓ C is correct.
®˚ A is incorrect because classes implement interfaces, they don’t extend them. B is incorrect because interfaces only “inherit from” other interfaces. D is incorrect based on the preceding rules.

2. Which method names follow the JavaBeans standard? (Choose all that apply.)
A. addSize
B. getCust
C. deleteRep
D. isColorado
E. putDimensions

Answer:
® ✓ B and D use the valid prefixes ‘get’ and ‘is’.
®˚ A is incorrect because ‘add’ can be used only with Listener methods. C and E are incorrect because ‘delete’ and ‘put’ are not standard JavaBeans name prefixes.

3. Given:
1. class Voop {
2.     public static void main(String[] args) {
3.         doStuff(1);
4.        doStuff(1,2);
5.     }
6.     // insert code here
7. }

Which, inserted independently at line 6, will compile? (Choose all that apply.)
A. static void doStuff(int… doArgs) { }
B. static void doStuff(int[] doArgs) { }
C. static void doStuff(int doArgs…) { }
D. static void doStuff(int… doArgs, int y) { }
E. static void doStuff(int x, int… doArgs) { }

Answer:
® ✓ A and E use valid var-args syntax.
®˚ B and C are invalid var-arg syntax, and D is invalid because the var-arg must be the last of a method’s arguments.

4. Given:
1. enum Animals {
2.     DOG(“woof”), CAT(“meow”), FISH(“burble”);
3.     String sound;
4.     Animals(String s) { sound = s; }
5. }
6. class TestEnum {
7.     static Animals a;
8.     public static void main(String [] args) {
9.         System.out.println(a.DOG.sound + ” ” + a.FISH.sound);
10.   }
11. }

What is the result?
A. woof burble
B. Multiple compilation errors
C. Compilation fails due to an error on line 2
D. Compilation fails due to an error on line 3
E. Compilation fails due to an error on line 4
F. Compilation fails due to an error on line 9

Answer:
® ✓ A is correct; enums can have constructors and variables.
®˚ B, C, D, E, and F are incorrect; these lines all use correct syntax.

5. Given two files:
1. package pkgA;
2. public class Foo {
3.     int a = 5;
4.     protected int b = 6;
5.     public int c = 7;
6. }
3. package pkgB;
4. import pkgA.*;
5. public class Baz {
6.     public static void main(String[] args) {
7.         Foo f = new Foo();
8.         System.out.print(” ” + f.a);
9.         System.out.print(” ” + f.b);
10.       System.out.print(” ” + f.c);
11.    }
12. }

What is the result? (Choose all that apply.)
A. 5 6 7
B. 5 followed by an exception
C. Compilation fails with an error on line 7
D. Compilation fails with an error on line 8
E. Compilation fails with an error on line 9
F. Compilation fails with an error on line 10

Answer:
® ✓ D and E are correct. Variable a has default access, so it cannot be accessed from outside the package. Variable b has protected access in pkgA.
®˚ A, B, C, and F are incorrect based on the above information.

6. Given:
1. public class Electronic implements Device
    { public void doIt() { } }
2.
3. abstract class Phone1 extends Electronic { }
4.
5. abstract class Phone2 extends Electronic
    { public void doIt(int x) { } }
7. class Phone3 extends Electronic implements Device
    { public void doStuff() { } }
8.
9. interface Device { public void doIt(); }

What is the result? (Choose all that apply.)
A. Compilation succeeds
B. Compilation fails with an error on line 1
C. Compilation fails with an error on line 3
D. Compilation fails with an error on line 5
E. Compilation fails with an error on line 7
F. Compilation fails with an error on line 9

Answer:
® ✓ A is correct; all of these are legal declarations.
®˚ B, C, D, E, and F are incorrect based on the above information.

7. Given:
4. class Announce {
5.     public static void main(String[] args) {
6.        for(int __x = 0; __x < 3; __x++) ;
7.            int #lb = 7;
8.            long [] x [5];
9.            Boolean []ba[];
10.          enum Traffic { RED, YELLOW, GREEN };
11.     }
12. }

What is the result? (Choose all that apply.)
A. Compilation succeeds
B. Compilation fails with an error on line 6
C. Compilation fails with an error on line 7
D. Compilation fails with an error on line 8
E. Compilation fails with an error on line 9
F. Compilation fails with an error on line 10

Answer:
® ✓ C, D, and F are correct. Variable names cannot begin with a #, an array declaration can’t include a size without an instantiation, and enums can’t be declared within a method.
®˚ A, B, and E are incorrect based on the above information.

8. Given:
3. public class TestDays {
4.     public enum Days { MON, TUE, WED };
5.     public static void main(String[] args) {
6.         for(Days d : Days.values() )
7.         ;
8.         Days [] d2 = Days.values();
9.         System.out.println(d2[2]);
10.    }
11. }

What is the result? (Choose all that apply.)
A. TUE
B. WED
C. The output is unpredictable
D. Compilation fails due to an error on line 4
E. Compilation fails due to an error on line 6
F. Compilation fails due to an error on line 8
G. Compilation fails due to an error on line 9

Answer:
® ✓ B is correct. Every enum comes with a static values() method that returns an array of the enum’s values, in the order in which they are declared in the enum.
®˚ A, C, D, E, F, and G are incorrect based on the above information.

9. Given:
4. public class Frodo extends Hobbit {
5.     public static void main(String[] args) {
6.        Short myGold = 7;
7.        System.out.println(countGold(myGold, 6));
8.    }
9. }
10. class Hobbit {
11.      int countGold(int x, int y) { return x + y; }
12. }

What is the result?
A. 13
B. Compilation fails due to multiple errors
C. Compilation fails due to an error on line 6
D. Compilation fails due to an error on line 7
E. Compilation fails due to an error on line 11

Answer:
® ✓ D is correct. The Short myGold is autoboxed correctly, but the countGold() method cannot be invoked from a static context.
®˚ A, B, C, and E are incorrect based on the above information.