The Collected "Hardest" Questions

When I started on the first Java Exam Cram book in 1999, I realized that creating good sample questions was not all that simple. As I worked up questions for the book I made them available for comment on-line using an applet that emulates the real test environment. Thanks to many useful comments from users, I was able to get rid of ambiguous or incorrect questions. Furthermore, by collecting every set of answers I was able to determine the question topics that caused users the most trouble. I selected a total of 19 questions that seemed to cover most of the exam objective areas and put them in a separate "Hardest" collection.

Taking these questions has been one of the options at my certification resources page since December 1999. There have been slight improvements in the questions as users have raised concerns (thanks folks!) I recently analyzed the collected results from over 65,000 individual tests, resulting in the following statistics. Note that the multiple choice - multiple correct answers questions did NOT give a hint as to the number correct because that was the style of the Sun exam at the time.

Question 1 type: Multiple choice - multiple correct answers possible

Here is the class hierarchy showing the ActionEvent family tree:

java.lang.Object
  |--- java.util.EventObject
         |---java.awt.AWTEvent
               |---- java.awt.event.ActionEvent

1. int evtCt = 0 ;
2. AWTEvent lastE ;
3. public void saveEvent( AWTEvent evt ){
4.   lastE = evt ;
5.   evtCt++ ;
6. }

Total answering = 65742 of which 22536 got it right.

Question 2 type: Multiple choice - multiple correct answers possible

Suppose we have two classes defined as follows:

 class ApBase extends Object implements Runnable
 class ApDerived extends ApBase implements Observer

  ApBase aBase = new ApBase() ;
  ApDerived aDer = new ApDerived();

 Object obj = aBase ;
   Runnable rn = obj ;

 Object obj = aBase ;
 Runnable rn = (Runnable) obj ;

 Object obj = aBase ;
 Observer ob = (Observer)aBase ;

 Object obj = aDer  ;
 Observer ob2 = obj ;

Total answering = 65771 of which 26448 got it right.

Question 3 type: Multiple choice - multiple correct answers possible

In the following code for a class in which methodA has an inner class.

 1. public class Base {
 2.   private static final int ID = 3 ;
 3.   private String name ;
 4.   public void methodA( final int nn ){
 5.     int serialN = 11 ;
 6.     class inner {
 7.       void showResult(){
 8.            System.out.println("Rslt= " + XX );
 9.       }
10.     } // end class inner
11.     new inner().showResult();
12.   } // end methodA
13. }

int ID

String name 

int nn

int serialN

Total answering = 65735 of which 29649 got it right.

Question 4 type: Multiple choice - single correct answer

What happens on trying to compile and run the following code?

1. public class EqualsTest{
2.   public static void main(String args[]){
3.     Long L = new Long( 7 );
4.     Integer J = new Integer( 7 ) ;
5.     if( L.equals( J )) System.out.println("Equal");
6.     else System.out.println("Not Equal");
7.   }
8. }

Total answering = 65702 of which 26355 got it right.

equals

Question 5 type: Multiple choice - single correct answer

What happens when we attempt to compile and run the following code?

1. public class Logic {
2.    static int minusOne = -1 ;
3.    static public void main( String args[] ){
4.       int N = minusOne >> 31 ;
5.       System.out.println("N = " + N );
6.    }
7. }

Total answering = 65698 of which 29984 got it right.

Question 6 type: Multiple choice - single correct answer

The following lists the complete contents of the file named Derived.java.

 1.  public class Base extends Object {
 2.      String objType ;
 3.      public Base(){  objType = "I am a Base type" ;
 4.      }
 5. }
 6.
 7. public class Derived extends Base {
 8.    public Derived() { objType = "I am a Derived type";
 9.    }
10.    public static void main(String args[] ){
11.       Derived D = new Derived();
12.    }
13. }

Total answering = 65692 of which 22989 got it right.

Question 7 type: Multiple choice - multiple correct answers possible

Once created, some Java objects are "immutable", meaning they can not have their contents changed. Which of the following classes produce immutable objects?

Total answering = 65688 of which 23751 got it right.

Question 8 type: Multiple choice - multiple correct answers possible

Trying to compile the following source code produces a compiler warning to the effect that the variable tmp may not have been initialized.

1. class Demo{
2.   String msg = "Type is " ;
3.   public void showType( int n ) {
4.    String tmp ;
5.    if( n > 0 ) tmp = "positive";
6.    System.out.println( msg + tmp );
7.  }
8. }

4.  String tmp = null ;

4.  String tmp = "" ;

6.    else tmp = "not positive" ;

 3.   String tmp ;

Total answering = 65693 of which 24479 got it right.

Question 9 type: Short text entry - case matters

The Greek letter pi in the Unicode used by Java has the value 3c0 in hexadecimal representation. Write the Unicode literal which would be used to initialize a char variable to pi. Just write the Unicode literal char, not the complete expression, in other words, what should replace XXXX in the following statement?

 char pic = XXXX ;

Total answering = 65690 of which 7990 got it right. A total of 4093 different text answers were recorded.

Question 10 type: Multiple choice - single correct answer

The following method definition is designed to parse and return an integer from an input string which is expected to look like "nnn,ParamName". In the event of a NumberFormatException, the method is to return -1.

1. public int getNum( String S ){
2.   try {
3.     String tmp = S.substring( 0,S.indexOf(','));
4.     return Integer.parseInt( tmp );
5.   }catch(NumberFormatException e){
6.     System.out.println("Problem in " + tmp );
7.   }
8.   return -1 ;
9. }

Total answering = 65683 of which 17004 got it right.

Question 11 type: Multiple choice - multiple correct answers possible

Given the following class definition:

1. public class DerivedDemo extends Demo{
2.   int M, N, L ;
3.   public DerivedDemo( int x, int y ){
4.     M = x ; N = y ;
5.   }
6.   public DerivedDemo( int x ){
7.     super( x );
8.   }
9. }

 public Demo( int a, int b )

 public Demo( int c )

 public Demo( )

Total answering = 65669 of which 27764 got it right.

Question 12 type: Multiple choice - multiple correct answers possible

Which of the following class declarations for a normal top level class are incorrect use of modifier keywords?

  public synchronized class FastClass extends Thread

  private protected class FastClass

  public abstract class FastClass

  class FastClass extends Thread

Total answering = 65664 of which 29258 got it right.

Question 13 type: Multiple choice - single correct answer

Given the following listing of the Widget class:

1. class Widget extends Thingee{
2.    static private int widgetCount = 0 ;
3.    public String wName ;
4.    int wNumber ;
5.
6.    static synchronized int addWidget(){ widgetCount++ ;
7.        wName = "I am Widget # " + widgetCount ;
8.        return widgetCount ;
9.    }
10.    public Widget(){
11.      wNumber = addWidget();
12.    }
13. }

Total answering = 65659 of which 22544 got it right.

Question 14 type: Multiple choice - multiple correct answers possible

(Questions like this with multiple correct answers are hard because you don't get partial credit, you have to get every one.) Select all of the following methods that are instance methods of the Thread class, excluding any methods deprecated in Java 1.2.

Total answering = 65651 of which 12030 got it right.

Question 15 type: Multiple choice - multiple correct answers possible

You are working on an applet which does animation. There is a single object animC, derived from java.awt.Canvas, which holds all the animation data and a memory image. There is a single Thread, animT which uses this data to create a new image for the next animation frame and then calls the following method.

1. synchronized void waitForPaint(){
2.    painted = false ; repaint();
3.    while( !painted ){
4.      try{ wait();
5.      }catch(InterruptedException x){}
6.    }
7. }

  synchronized(this){painted = true ; notify();}

Total answering = 65645 of which 13759 got it right.

Question 16 type: Multiple choice - multiple correct answers possible

The GenericFruit class declares the following method.

 public void setCalorieContent( float f )

Select all of the following which would constitute legal declarations of overloading methods.

 protected float setCalorieContent(String s )

 protected void setCalorieContent( float x )

 public void setCalorieContent( double d )

 public void setCalorieContent(String s ) throws NumberFormatException

Total answering = 65638 of which 24949 got it right.

Question 17 type: Multiple choice - multiple correct answers possible

Here is the hierarchy of Exceptions related to array index errors.

 Exception
    +-- RuntimeException
           +-- IndexOutOfBoundsException
                  +-- ArrayIndexOutOfBoundsException
                  +-- StringIndexOutOfBoundsException

Total answering = 65634 of which 13372 got it right.

Question 18 type: Multiple choice - multiple correct answers possible

The following method is designed to convert an input string to a floating point number, while detecting a bad format. Assume that

factor

1. public boolean strCvt( String s ){
2.   try {
3.     factor = Double.valueOf( s ).doubleValue();
4.     return true ;
5.   }catch(NumberFormatException e){
6.     System.out.println("Bad number " + s );
7.     factor = Double.NaN ;
8.   }finally { System.out.println("Finally");
9.   }
10.  return false ;
11. }

Total answering = 65624 of which 16598 got it right.

Question 19 type: Multiple choice - multiple correct answers possible

Given the following code fragment:

 XXXX x ; // variable x is declared and initialized here
 switch( x ) {
   case 100 : System.out.println("One hundred");break ;
   case 200 : System.out.println("Two hundred");break ;
   case 300 : System.out.println("Three hundred");break ;
 }

byte x = 100 ;

short x = 200 ;

int x = 300 ;

long x = 400 ;

Total answering = 65617 of which 15749 got it right.

 switch((int)x) {

Summary of Scores

Number scoring 100% 1021
Number scoring between 90.0% and 99.9% = 1727
Number scoring between 80.0% and 89.9% = 3588
Number scoring between 70.0% and 79.9% = 4108
Number scoring between 60.0% and 69.9% = 4701
Number scoring between 50.0% and 59.9% = 5284
Number scoring between 40.0% and 49.9% = 5754
Number scoring between 30.0% and 39.9% = 5669
Number scoring between 20.0% and 29.9% = 5666
Number scoring between 10.0% and 19.9% = 6366
Number scoring between 0.0% and 9.9% = 21857