Interview Questions and Answers

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Q: 23 Given:
1. package sun.scjp;
2. public enum Color { RED, GREEN, BLUE }
1. package sun.beta;
2. // insert code here
3. public class Beta {
4. Color g = GREEN;
5. public static void main( String[] argv)
6. { System.out.println( GREEN); }
7. }
The class Beta and the enum Color are in different packages.
Which two code fragments, inserted individually at line 2 of the Beta
declaration, will allow this code to compile? (Choose two.)
A. import sun.scjp.Color.*;
B. import static sun.scjp.Color.*;
C. import sun.scjp.Color; import static sun.scjp.Color.*;
D. import sun.scjp.*; import static sun.scjp.Color.*;
E. import sun.scjp.Color; import static sun.scjp.Color.GREEN;
Answer: CE
Question 24
Given:
10. public class Fabric
11. public enum Color {
12. RED(0xff0000), GREEN(0x00ff00), BLUE(0x0000ff);
13. private final int rgb;
14. Color( int rgb) { this.rgb = rgb; }
15. public int getRGB() { return rgb; }
16. };
17. public static void main( String[] argv) {
18. // insert code here
19. }
20. }
Which two code fragments, inserted independently at line 18, allow the
Fabric class to compile? (Choose two.)
A. Color skyColor = BLUE;
B. Color treeColor = Color.GREEN;
C. Color purple = new Color( 0xff00ff);
D. if( RED.getRGB() < BLUE.getRGB() ) {}
E. Color purple = Color.BLUE + Color.RED;
F. if( Color.RED.ordinal() < Color.BLUE.ordinal() ) {}
Answer: BF
25. Given the following,
1. interface Base {
2. boolean m1 ();
3. byte m2(short s);
4. }
Which code fragments will compile? (Choose all that apply.)
A. interface Base2 implements Base { }
B. abstract class Class2 extends Base {
public boolean m1() { return true; } }
C. abstract class Class2 implements Base { }
D. abstract class Class2 implements Base {
public boolean m1() { return (true); } }
E. class Class2 implements Base {
boolean m1() { return false; }
byte m2(short s) { return 42; } }
Answer:
-> C and D are correct. C is correct because an abstract class doesn't have to implement any or all of its interface's methods. D is correct because the method is correctly implemented.
-> A is incorrect because interfaces don't implement anything. B is incorrect because classes don't extend interfaces. E is incorrect because interface methods are implicitly public, so the methods being implemented must be public.
26. Which declare a compilable abstract class? (Choose all that apply.)
A. public abstract class Canine { public Bark speak(); }
B. public abstract class Canine { public Bark speak() { } }
C. public class Canine { public abstract Bark speak(); }
D. public class Canine abstract { public abstract Bark speak(); }
Answer:
->B is correct. abstract classes don't have to have any abstract methods.
-> A is incorrect because abstract methods must be marked as such. C is incorrect becauseyou can't have an abstract method unless the class is abstract. D is incorrect because thekeyword abstract must come before the classname. (Objective 1.1)
27. 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.

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