Test Yourself: Fundamentals, Part 2

I recommend that you also make use of my online Java tutorial lessons
which are designed from a more conventional textbook approach.  Those
tutorial lessons are published at Gamelan.com.

For your convenience, I also maintain a consolidated  Table
of Contents on my personal web site that links to the individual lessons
on the Gamelan site.

Insofar as possible, I will make use of Sun
Java in these lessons.  However, it will not be possible for me
to go back and do a full update each time Sun releases a new version, so
over the course of time, I expect to use different versions of Sun Java.

Just in case you would like to sneak a peek, the answers
to the questions, and the explanations of those answers are located (in
reverse order) at the end of this file.

The questions and the answers are connected by hyperlinks to make it
easy for you to navigate from the question to the answer and back. 
It is recommended that you make your first pass through the questions in
the order that they appear so as to avoid inadvertently seeing the answer
to a question before you provide your own answer.

Answer and Explanation

2. boolean states:  Which of the
following are the possible states of a boolean variable?

• A.  true
• B.  uncertain
• C.  false

Answer and Explanation

3. Range of integer types:  The following
table purports to show the numeric range of the integer types in terms
of a power of two.  Identify which lines, if any, contain errors. 
(The syntax 2eX means 2 raised to the X power.)

 

Answer and Explanation

4.  Signed versus unsigned  True or
false?  All of the integral types, including char are signed.

Answer and Explanation

5.  Character representation:  True
or false?  Characters in Java are represented by the 8-bit Extended
ASCII character set.

Answer and Explanation

6.  Unicode to ASCII relationship: 
What is the relationship between the 16-bit Unicode character set and the
7-bit ASCII character set.

Answer and Explanation

7.  Invalid numeric values:  As a
result of certain arithmetic operations (such as division by zero), certain
primitives can take on bit patterns that do not represent valid numeric
values.  These possibilities are represented by symbolic constants
in the various classes.  Which of the following are not valid symbolic
constants?

• A.  Integer.NaN
• B.  Integer.NEGATIVE_INFINITY
• C.  Integer.POSITIVE_INFINITY
• D.  Float.NaN
• E.  Float.NEGATIVE_INFINITY
• F.  Float.POSITIVE_INFINITY
• G.  Double.NaN
• H.  Double.NEGATIVE_INFINITY
• I.  Double.POSITIVE_INFINITY

Answer and Explanation

8.  Literal values:  Which, if any,
of the following are not valid literal values for type char?

• A.  'u1632'
• B.  't'
• C.  "a"
• D.  'end'

Answer and Explanation

9.  Escape characters:  Which of the
following are valid escape characters in Java?

• A.  'n'
• B.  'r'
• C.  't'
• D.  'b'
• E.  'f'
• F.  '''
• G.  'q'
• H.  's'
• I.  '"'
• J.  ''

Answer and Explanation

Bonus question.  The following question is considerably
more difficult than the previous nine questions, and is included here to
challenge you if the previous nine questions have been too easy.

10.  Bit manipulations:  What output
is produced by the following program?

• A.  1
• B.  -1
• C.  2
• D.  -2

class Q002_10{
   public static void main(String args[]){
     int x = 1;
     int y = ~x + 1;
     System.out.println(y);
   }//end main()
 }//end class definition

Answer and Explanation

About the author

Richard Baldwin
is a college professor and private consultant whose primary focus is a
combination of Java and XML. In addition to the many platform-independent
benefits of Java applications, he believes that a combination of Java and
XML will become the primary driving force in the delivery of structured
information on the Web.

Richard has participated in numerous consulting projects involving
Java, XML, or a combination of the two.  He frequently provides onsite
Java and/or XML training at the high-tech companies located in and around
Austin, Texas.  He is the author of Baldwin’s Java Programming Tutorials,
which has gained a worldwide following among experienced and aspiring Java
programmers. He has also published articles on Java Programming in Java
Pro magazine.

Richard holds an MSEE degree from Southern Methodist University and
has many years of experience in the application of computer technology
to real-world problems.

baldwin.richard@iname.com

Back to Question

In fact, this is how you convert a positive twos complement binary value
to a negative twos complement binary value (or vice versa).  First
you invert all of the bits.  Then you add 1.

Back to Question

• A.  'n' Newline
• B.  'r' Return
• C.  't' Tab
• D.  'b' Backspace
• E.  'f' Formfeed
• F.  ''' Apostrophe or single quote
• G.  'q' Not
  valid
• H.  's' Not
  valid
• I.  '"' Double quote
• J.  '' Backslash

Back to Question

B.  ‘t’ is also a valid literal value of type char. 
This is the so-called escape character that represents a Tab. 
There are about eight such escape characters supported by Java that represent
various things like Tab, Newline, Return, Backspace,
etc.

C.  “a” is not a valid literal of type char. 
Rather, this is a String literal.

In Java, unlike some other languages, quotation marks (“) and apostrophes
(‘) have entirely different meanings.

Zero or more characters surrounded by quotation marks are interpreted
by the compiler to constitute a String literal.

Any single character surrounded by apostrophes is interpreted by the
compiler to be a char literal.  When confronted with such a
literal, the compiler produces the numeric value that represents that character. 
For example, the following code fragment will cause the value 65 to be
displayed because the numeric value that represents the upper-case A in
the Unicode character set is 65.

    int data = ‘A’;

    System.out.println(data);

D.  ‘end’ has no meaning in Java.  Unlike some other
languages, such as Python, you cannot interchange quotation marks and apostrophes
when creating strings.  For example, the following statement will
produce the compiler error “Invalid character constant”

    System.out.println(‘end’);

Back to Question

An object of the Integer class is intended to encapsulate an
int
value.  There are no operations that you can perform with an int
that results in a bit pattern that does not represent a valid numeric value.

While it is possible to end up with erroneous int values as a
result of some arithmetic operations, they are still valid numeric values
and so there is no need for the kind of symbolic constants described for
float
and double in this question.

Back to Question

As it turns out, for those of us who program using the U.S./English
alphabet, the change from Extended ASCII to Unicode isn’t very significant. 
We can pretty much continue doing what we have been doing for years.

However, those who program using alphabets from other spoken languages
now have the ability to reflect those languages in the character representations
contained in their programs.

Back to Question

However, Java does not use the ASCII character
set.  Java characters are expressed as 16-bit Unicode characters.
(To learn more about Unicode characters, visit the following URL.)

 

Back to Question

Back to Question

In summary, this means that a variable containing n bits has
the following numeric range (where 2eX means 2 raised to the X power):

Minimum = -2e(n-1)

Maximum = (2e(n-1))-1

Consider the following simple example.  Assume that n is
equal to 3.  Then:

Minimum = -2e(3-1) = -4

Maximum = (2e(3-1))-1 = 4-1 = 3

A three-bit variable can represent eight different combinations of bits. 
In two’s complement notation, it can represent the range of integer values
from -4 to +3.  Here is how the bits would be organized to represent
those values in two’s complement binary notation.

 

Back to Question

The boolean type is often used in conditional expressions to make a
choice between two possibilities.  For example, the following construct
would not work properly if the boolean were allowed to have the third value
uncertain. 
In that case, you might find yourself stranded on the roadside with an
empty gas tank.

if(gasInTank < 1)

  buyGas(); //need to buy gas

else

  keepDriving();//don't need to buy gas

 

Back to Question

You may wonder why this is the case.  One of the primary reasons
is the need to internationalize computer technology.  An 8-bit character
set can represent only 255 different characters.  During that part
of history when most computer technology was based on the U.S./English
alphabet, this was sufficient.  However, computer technology is no
longer so confined, and there is a need to be able to represent more than
255 characters.

The 16-bit Unicode set makes it possible to represent more than 65,000
different characters.  Hopefully this will be sufficient to represent
the alphabets of all countries in the international computer technology
arena.

You may also wonder about the correctness of line A which indicates
that the boolean type is 1 bit in size.  I personally don’t
know exactly how a boolean variable is represented in memory, but
I would have guessed that it is stored in an 8-bit byte.  I also don’t
know how to write any code that will expose the manner in which a boolean
variable is stored in memory.

The size of one bit for a boolean is based on information from
the book entitled The Complete Java 2 Certification Study Guide
by Roberts, Heller, and Ernest.  A boolean certainly could
be stored in a single bit since only two different values must be represented. 
This assumes, of course, that the processor has the ability to address
memory down to the single-bit level.

In the final analysis, it probably doesn’t matter.  Unlike C and
C++, you cannot do arithmetic with a boolean, and I can’t think
of any other operation that you can perform on a boolean where the
manner in which it is stored in memory makes any difference (except possibly
for speed).

About the author

Richard Baldwin
is a college professor and private consultant whose primary focus is a
combination of Java and XML. In addition to the many platform-independent
benefits of Java applications, he believes that a combination of Java and
XML will become the primary driving force in the delivery of structured
information on the Web.

Richard has participated in numerous consulting projects involving
Java, XML, or a combination of the two.  He frequently provides onsite
Java and/or XML training at the high-tech companies located in and around
Austin, Texas.  He is the author of Baldwin’s Java Programming Tutorials,
which has gained a worldwide following among experienced and aspiring Java
programmers. He has also published articles on Java Programming in Java
Pro magazine.

Richard holds an MSEE degree from Southern Methodist University and
has many years of experience in the application of computer technology
to real-world problems.

baldwin.richard@iname.com