Java Quiz

Read the following piece of code carefully

public abstract class AbstractClass
{
     public AbstractClass()
     {
          System.out.println("this is an abstract class constructor!");
     }

     public void aMethod()
     {
          System.out.println("This is in the method in the abstract class");
     }

}

1. Compiler error - abstract classes cannot have constructors.
2. Compiler error - the method AbstractClass does not have a valid return type.
3. Compiler error - the class cannot be declared as abstract as it does not have any unimplemented methods.
4. No compiler error - the class is practically not an abstract class and can be instantiated.
5. No compiler error - the class cannot be instantiated directly. It has to be extended to an non-abstract class. The constructors of the extended class will call the constructor of the abstract class (implicitly or explicitly).
6. No compiler error - the class cannot be instantiated directly. It has to be extended to an non-abstract class. The constructors of the abstract class will never be called.

Question 72.

Read the following piece of code carefully.

import java.io.IOException;
 

public class Question72
{
    public Question72() throws IOException
    {
        throw new IOException();
    }
}

    public class Question72E extends Question72

It is required that none of the constructors of Question72E should throw any checked exception.
 

1. It can be achived by placing the call to the superclass with  a super keyword , which is placed in a try block with a catch block to handle the IOException thrown by the super class.
2. It can be achived by avoiding explicit calls to the base class constructor.
3. It cannot be done in the Java Laungage with the above definition of the base class.

Question 73.

Read the following piece of code carefully. (This is an extention to question 72.)

public abstact class Question73 extends Question72
{
    public abstract void method();
}

An attempt to compile the above class definition

1. will cause a compiler error - non-abstract classes cannot be extended to abstract classes.
2. will cause a compiler error - a constructor must be provided which may or may not throw an IOException
3. will cause a compiler error - a constructor must be provided which must throw an IOException or one of its super types.
4. will not cause any compiler error. The class definition is perfectly legal.

Question 74.

Read the following piece of code carefully.
 

class Base
{
    Base()
    {
        System.out.println("Message 1 : In the base class constructor");
    }
}

abstract class Derived1 extends Base
{
    Derived1()
    {
        System.out.println("Message 2 : In the abstract class Derived1\'s constructor");
    }
}

public class Derived2 extends Derived1
{
    public Derived2()
    {
        System.out.println("Message 3 : In the derived2 class\'s constructor.");
    }
 
    public static void main(String args[])
    {
        Derived2 d2 = new Derived2();
    }
}

1. will cause a compiler error. The non-abstract classes cannot be extended to the abstract classes.
2. will cause a compiler error.  The abstract classes cannot have constructors defined.
3. will not cause any compiler error. The lines "Message 1..." and "Message 3 ... " are printed on the screen.
4. will not cause any compiler error. The lines "Message 1..." and "Message 2...." and Message 3...." are printed on the screen.

Question 75.

Read the following piece of code carefully.
 

public class A
{
    A()
    {
    }
}

1. The class A can be referenced outside the package in which it is defined.
2. The class A cannot be instantiated outside the package in which it is defined.
3. The class A cannot be extended outside the package in which it is defined.
4. The class A can be referenced, instantiated or extended anywhere.
5. The above code will cause a compiler error. The constructors of public class have to be public.

Question 77.

    If the finalize() method of an object is re-references an object so that it becomes in-eligible for garbage collection
 

1. The compiler will throw an error.
2. The garbage collector "collects" the object anyway.
3. The garbage collector does not collect the object in the present sweep. But when the object becomes eligible for garbage collection again, its finalize method will not be called by the garbage collector (i.e., if the garbage collector gets a chance to run.). It will simply be garbage collected.
4. The object can never be garbage collected and hence leads to memory-leak. Each time the garbage collector calls finalize before "collecting" the object the object "resurrects" itself.

Question 78.

    If a Runtime Exception is thrown in the finalize method -
 

1. The running application crashes.
2. The exception is simply ignored and the object is garbage collected.
3. The exception is simply ignored, but the object is not garbage collected.
4. The Exception causes the JVM to crash.

Question 79.

The factory class java.util.Collections

1. is public
2. implements the java.util.Collection interface.

Question 80.
 

import java.io.*;

     public class TransientWriter implements Externalizable
     {
 
         private transient String s = "Hope I can ever be persistant!";

         public void writeExternal(ObjectOutput oOut) throws IOException
         {
             oOut.writeObject(s);
         }
 
         public void readExternal(ObjectInput oIn) throws IOException, ClassNotFoundException
         {
             s=(String)oIn.readObject();
         }

   public String toString()
   {
    return s;
   }
     }

  class K
  {
   public static void main(String args[]) throws IOException, ClassNotFoundException
   {
   TransientWriter tw = new TransientWriter();
   ObjectOutputStream out = new ObjectOutputStream(new FileOutputStream("tw.out"));
   out.writeObject(tw);

   ObjectInputStream in = new ObjectInputStream(new FileInputStream("tw.out"));

   TransientWriter tw2 = (TransientWriter) in.readObject();
   System.out.println(tw2);
  }
 }

Attempting to compile and run the above code
 

1. will cause a compiler error due to the attempt to write a transient object.
2. will cause a runtime exception when an attempt is made to write a transient object.
3. will not cause any runtime error and the transient object is writen to the file named "tw.out".
4. will not cause any runtime error and the transient object is not written to the file named "tw.out". The program prints a blank line on the screen.