Java Interview Questions - 6

Which of the following statements about arrays is syntactically wrong?
(a) Person[] p = new Person[5];
(b) Person p[5];
(c) Person[] p [];
(d) Person p[][] = new Person[2][];
Java Interview Questions


2. Given the following piece of code:
public class Test {
public static void main(String args[]) {
int i = 0, j = 5 ;
for( ; (i < 3) && (j++ < 10) ; i++ ) {
System.out.print(" " + i + " " + j );
}
System.out.print(" " + i + " " + j );
}
}
what will be the result?
(a) 0 6 1 7 2 8 3 8
(b) 0 6 1 7 2 8 3 9
(c) 0 5 1 5 2 5 3 5
(d) compilation fails


3. Which of the following declarations is correct? (2 answers):
(a) boolean b = TRUE;
(b) byte b = 255;
(c) String s = “null”;
(d) int i = new Integer(“56”);


4. Suppose a class has public visibility. In this class we define a protected method. Which of the following statements is correct?
(a) This method is only accessible from inside the class itself and from inside all subclasses.
(b) In a class, you can not declare methods with a lower visibility than the visibility of the class in which it is defined.
(c) From within protected methods you dnot have access tpublic methods.
(d) This method is accessible from within the class itself and from within all classes defined in the same package as the class itself.


5. Given the following piece of code:
public class Company{
public abstract double calculateSalaries();
}
which of the following statements is true?
(a) The keywords public and abstract can not be used together.
(b) The method calculateSalaries() in class Company must have a body
(c) You must add a return statement in method calculateSalaries().
(d) Class Company must be defined abstract.


6. Given the following piece of code:
public interface Guard{
void doYourJob();
}
abstract public class Dog implements Guard{}
which of the following statements is correct?
(a) This code will not compile, because method doYourJob() in interface Guard must be defined abstract.
(b) This code will not compile, because class Dog must implement method doYourJob() from interface Guard.
(c) This code will not compile, because in the declaration of class Dog we must use the key-word extends in stead of implements.
(d) This code will compile without any errors.


7. Given these classes:
public class Person{
public void talk(){ 
System.out.print("I am a Person "); 
}
}
public class Student extends Person {
public void talk(){ 
System.out.print("I am a Student "); 
}
}
what is the result of this piece of code:
public class Test{
public static void main(String args[]){
Person p = new Student();
p.talk();
}
}
(a) I am a Person
(b) I am a Student
(c) I am a Person I am a Student
(d) I am a Student I am a Person


8. Given the following piece of code:
public class Person{
private String firstName;
public Person(String fn){ 
firstName = fn; 
}
}
public class Student extends Person{
private String studentNumber;
public Student(String number) { 
studentNumber = number; 
}
}
Which of the following statements is true? (2 answers)
(a) This code will compile if we define in class Person a no-argument constructor.
(b) This code will compile if we define in class Student a no-argument constructor.
(c) This code will compile if we add in the constructor of Student the following line of code as first statement:super();
(d) This code will compile if we call the constructor of Person from within the constructor of Student.


9. Specify the correct characteristics of an enumeration type (2 answers)
(a) enum can define static fields and methods 
(b) enum can contain a public constructor
(c) enum can implement interfaces
(d) enum is a reference ta variable set of constants


10. Given the following piece of code:
class Person { 
public int number; 
}

public class Test{
public void doIt(int i , Person p){
i = 5;
p.number = 8;
}
public static void main(String args[]){
int x = 0;
Person p = new Person();
new Test().doIt(x, p);
System.out.println(x + " " + p.number);
}
}
What is the result?
(a) 0 8
(b) 5 0
(c) 0 0
(d) 5 8


11. Given the following piece of code:
class SalaryCalculationException extends Exception{}
class Person{
public void calculateSalary() throws SalaryCalculationException {
//...
throw new SalaryCalculationException();
//...
}
}
class Company{
public void paySalaries(){
new Person().calculateSalary();
}
}
Which of the following statements is correct? (2 answers)
(a) This code will compile without any problems.
(b) This code will compile if in method paySalaries() we return a boolean in stead of void.
(c) This code will compile if we add a try-catch block in paySalaries() 
(d) This code will compile if we add throws SalaryCalculationException in the signature of method paySalaries().


12. Which of the following statements regarding static methods are correct? (2 answers)
(a) static methods are difficult tmaintain, because you can not change their implementa-tion.
(b) static methods can be called using an object reference tan object of the class in which this method is defined.
(c) static methods are always public, because they are defined at class-level.
(d) static methods dnot have direct access tnon-static methods which are defined inside the same class.


13. Given the following piece of code:
class Person{ 
public void talk(){} 
}
public class Test{
public static void main(String args[]){
Person p = null;
try{
p.talk();
} catch(NullPointerException e){
System.out.print("There is a NullPointerException. ");
} catch(Exception e){
System.out.print("There is an Exception. ");
}
System.out.print("Everything went fine. ");
}
}
what will be the result?
(a) If you run this program, the outcome is: There is a NullPointerException. Everything went fine.
(b) If you run this program, the outcome is: There is a NullPointerException.
(c) If you run this program, the outcome is: There is a NullPointerException. There is an Exception.
(d) This code will not compile, because in Java there are npointers.


14. Which of the following statement about Generics are correct? (2 answers)
(a) Generics are typed subclasses of the classes from the Collections framework
(b) Generics are used tparameterize the collections in order tallow for static type check-
ing at compile tIme of the objects in the collection.
(c) Generics can be used tperform type checking of the objects in a collection at runtime.
(d) Generics can be used titerate over a complete collection in an easy way, using the ‘enhanced for’ loop.


15. Which collection class associates values witch keys, and orders the keys according ttheir natural order?
(a) java.util.HashSet
(b) java.util.LinkedList
(c) java.util.TreeMap
(d) java.util.SortedSet


16. Which of the following statements about GUI components is wrong?
(a) Swing exists since version 1.2 of the jdk.
(b) AWT stands for Abstract Window Toolkit
(c) You can not place AWT components on Swing containers.
(d) The AWT classes are deprecated.


17. Which of the following statements about events are correct? (2 answers)
(a) Event objects are placed on a Queue, where they are fetched by subscribers (objects of classes which implement the interface Subscriber).
(b) The listener of an event must implement the method public void listen(EventObject obj).
(c) Each event object must be an object of a subclass of EventObject.
(d) Each event listener can investigate about the source of an event by calling the method getSource() on the event object.


18. How can you serialize an object?
(a) You have tmake the class of the object implement the interface Serializable.
(b) You must call the method serializeObject()(which is inherited from class Object) on the object.
(c) You should call the static method serialize(Object obj) from class Serializer, with as argument the object tbe serialized.
(d) You don’t have tdanything, because all objects are serializable by default.


19. Which statements about Iare correct (2 answers)?
(a)OutputStream is the abstract superclass of all classes that represent an outputstream of bytes.
(b) Subclasses of the class Reader are used tread character streams.
(c) Twrite characters tan outputstream, you have tmake use of the class CharacterOutputStream.
(d) Twrite an object ta file, you use the class ObjectFileWriter.


20. Given the following piece of code:
public class MyThread extends Thread{
public String text;
public void run(){
System.out.print(text);
}
}
public class Test{
public static void main(String args[]){
MyThread t1 = new MyThread(); t1.text = "one ";
MyThread t2 = new MyThread(); t2.text = "tw";
t1.start();
t2.start();
System.out.print("three ");
}
}
Which of the following statements is true?
(a) If you execute this program, the result is always one twthree
(b) If you execute this program, the result is always three one two
(c) The result of this program is undetermined.
(d) Compilation will faill.


Answers:

1. b
2. a
3. c, d
4. d
5. d
6. d
7. b
8. a, d
9. a, c
10. a
11. c, d
12. b, d
13. a
14. b, d
15. c
16. d
17. c, d
18. a
19. a, b
20. c

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