Transcript On the (un)suitability of Java to be the first programming

On the (un)suitability of Java to be
the first programming language
Mirjana Ivanovic
Faculty of Science,
Department of Mathematics and Informatics
Trg Dositeja Obradovica 4, Novi Sad
[email protected]
Klaus Bothe
Humboldt-University, Institute of Informatics
Rudower Chaussee 25, Berlin
[email protected]
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On the (un)suitability of Java to be the first
programming language - LITERATURE
[1] L. Boeszoermenyi: “Why Java is not my favorite first-course
language”, Software Concepts and Tools.
[2] http://www.cs.rit.edu/~ncs/Uppsala97 - “Using Java in
Computer Science Education – Panel”
[3] M. Koelling, B. Koch, J. Rosenberg: “Requirements for a
First Year Object-Oriented Teaching Language”
[4] Author’s experiences
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Choice of First Programming Language
How we learn something for the first time seems to
have particular importance
Nobody can learn a programming language
properly
just by using it
without using it
First programming language serves as a reference
for learning additional programming languages
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Choice of First Programming Language
No best paradigm - the importance of historical point of view.
Is object-oriented development the right way to go? [1]
For many purposes it is the wrong approach (the concept of
modularization is much more fundamental then that of objectorientation).
There is one single “right way” that universities should try to find and
teach.
Direction of historical development has not been an accident –
programming started with basic concepts as notion of constant, variable,
algorithm and function (procedure) – not with notion of objects.
All this does not imply that we cannot start with OO, but it surely
follows that we do not have to start with it.
For example: it is true that every sequential program can be regarded as a
special case of parallel program. – Is it good idea to start teach with parallel
programming?
“My experience suggest that it is better to start with the classical basic
concepts and to introduce OO on top of them.” - L. Boeszoermenyi
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Choice of First Programming Language
Requirements for the first programming course [1], [4]
It must teach the most basic concepts of programming
It must teach them in a way that
the student can use them as a reference for advanced concepts
and advanced programming notions.
That makes students understand that programming paradigms
and languages and their concepts are under steady development
and (hopefully) improvement.
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Choice of First Programming Language
First of all the question is which paradigm to use in
first programming course?
Procedural
Object-oriented
Declarative
Parallel 
It is necessary to analyze
Good and bad features of language
Quality, reliability, friendly environment
Pascal-like or C (Java)-like languages
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Choice of First Programming Language
20th edition 4-8-99, of the list of the languages used in the
FIRST course for Computer Science majors at Colleges and
Universities that have sent in their listing (597 Institutions).
Pascal
C + C++
Ada
Modula + Oberon
Scheme
ML +SML+Haskell
Java
SmallTalk + Simula
Other
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74 + 103
101
50 + 4
53
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15
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Choice of First Programming Language
Modern trends in IT
New dimension – complexity of software development
Distributed client/server architectures
Internet, WWW, E-Business
Some characteristic problems of software development
for Internet
Security – non-authorized access
Lack of specialized language for Internet applications
Real interaction in Internet applications
Non-portability
Solution?
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Choice of First Programming Language
Solution - JAVA?
Java is new fashionable, and to argue against fashion is very
similar to fighting against the wind  [1].
“Simple” object-oriented language
Faster software life-circle - JAVA is interpretative language
Portability
Application robustness – memory management
Better performances for interactive graphics applications
Possibility for development of adaptable applications – reactivity
to changes in run-time environment
Built-in virus protection in JAVA run-time system
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JAVA in Real-life Applications
Types of Java applications
Stand-alone applications
Applets
Java programs as parts of Web documents
Java code as a part of HTML documents
Interactive applications
Games, commercials, home-page refinement,
simulations of real-life situations
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Humboldt-University: history of introductory
languages in the 1st semester
up to 1975:
Algol 60
imperative (algorithmic)
languages
1976 – 1984:
Pascal
1985 – 1996:
Modula-2
modularisation, data
abstraction
from 1997:
Java
object-orientation
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1st reason for switching to Java (Humboldt):
students motivation
about 1992 – 1996:
Students complain about the “outdated” language
Modula-2
(outdated = no more used in practice)
Students vote for C, C++
(We argued: C, and thus C++, are too unsystematic from the
point of view of education.)
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2nd reason for switching to Java (Humboldt):
Java becomes broadly excepted at universities
1995 / 96:
A lot of German universities and universities
all over the world start with Java in the 1st
semester
HU students become aware of this
development
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3rd reason for switching to Java (Humboldt):
Java becomes broadly excepted in industry
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Fortran
Asmb.
Delphi /
Pascal
PL1
Java
Visual
Basic
Cobol
C
C++
languages used in German industry in 1998
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4th reason for switching to Java (Humboldt):
OO can be introduced from the very beginning
Program paradigms:
1960
1980
1986 / 95
imperative / algorithmic
modular
OO
Many new projects in industry start with OO languages
OO prog. should be taught at universities very early
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5th reason for switching to Java (Humboldt):
Pre-knowledge of the beginners
New students in first semester already know
a lot from school and from self-study when
they start at university:
Pascal, Basic, C, C++, ...
New beginners even know Java ...
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Faculty of Science, Novi Sad: history of introductory
languages in the 1st semester
1979-1983: No PL in 1st semester
FORTRAN in 3rd semester
1984–1990: Pascal
Imperative (algorithmic)
approach
from 1991: Modula-2
Modularisation, data
abstraction
Now:
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Java?
Object-orientation?
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Reasons for thinking to switch to Java
Java becomes broadly excepted at universities
Java becomes broadly excepted at industry
Pressure of modern world trends in IT and acceptably of
Java in IT community
Students complain about the “outdated” language
Modula-2 and mostly voted for C-like languages
Outdated = no more used in practice, not modern(?)
We argued: C, and thus C++, are too unsystematic from educational
purposes
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Main reasons not to switch to Java as first PL
Teaching Java as a part of Programming language course (III, IV
semesters).
Some of students have no any experience with programming and
programming languages.
Most of students have pre-knowledge based on imperative (algorithmic)
programming languages (Pascal, BASIC, C).
Dilemma: whether OO concepts should be taught at universities very
early?
Modular languages (Pascal, Modula,…) are still very good languages for
teaching and learning basic, systematic, algorithmic programming style
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Java – general opinions: good, bad, ugly - GOOD
“Simple”, concise language
Implementation of essential concepts of programming languages
Compile-time error checking and diagnosis
Expressiveness, advanced features
Missing pointers
Reliable objects – garbage collection
Single inheritance, interfaces – multiple inheritance
Real portability, exception handling, serialization
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Java – general opinions: good, bad, ugly - BAD
C++ syntax
Switch statement – unusual semantics
Existence of empty statement
For (int i=0;i<10;i++);
Unusual usage of == for equality test, = for
assignment
A grate number of confusing operators
x +=i++; (x :=x+i; i:=i+1)
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Java – general opinions: good, bad, ugly - UGLY
C++ syntax, { } as block delimiters, statement bodies, …
Static – specification of class elements
Complex and confusing I/O, reading an integer
BufferedReader kbd = new BufferedReader
(new InputStreamReader(System.in));
Integer.ValueOf(kbd.readLine()).intValue()
Existance of special new operator
MyClass a= new MyClass();
(instead of: MyClass a= MyClass.new(); )
Complex structure even for simple programs
public class MyProgram {
public static void main (string args[])
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{...} }
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Problems of Java as the first programming language (1)
Before (besides) introducing OO: conventional imperative
language constructs have to be introduced:
data types, variables
statements, algorithms, procedures
Solution at HU: Two main parts of Java introduction:
Part I: imperative constructs of Java
Part II: object-orientation with Java
Disadvantage: Imperative programming in the framework of
an OO language
- is a bit ‘unnatural’ (K. Bothe)
- could be too difficult for beginners and puts an unnecessary burden on
the students (L. Boeszoermenyi, M. Ivanovic)
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Problems of Java as the first programming language (2)
The class concept in Java is no real concept to
introduce abstraction or information hiding – it is
just implementation.
Modula-2:
definition module =
what the user has to know about the module
implementation module =
implementation details (data, algorithms)
which are hidden from the user
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Problems of Java as the first programming language (3)
The lack of notion of procedure, modes of parameter
passing and references.
procedure is a special case of method
Parameter passing: simple types are passed value; objects
are passed by reference.
Modula-3 procedures that swaps 2 integer values:
PROCEDURE Swap(VAR int1, int2:INTEGER);
VAR x:INTEGER;
BEGIN
x:=int1; int1:=int2; int2:=x
END Swap;
In Java this procedure is actually not implementable.
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Problems of Java as the first programming language (3)
The lack of notion of procedure, modes of parameter
passing and references.
In many well-known algorithms, the lack of VAR
parameters leads to necessary complications.
More real example - Most implementations of an insert
(delete) operation of an AVL tree use a Boolean VAR
parameter (height) to show whether the tree was grown
(reduced) at the last recursion level. To realize this in
Java, we need a special object just to store a Boolean
value. We, may, of course also change the algorithm, e.g.,
by turning the insert procedure into a function. In the
case of deletion we need a more sophisticated change.
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Problems of Java as the first programming language (4)
To “catch” the C / C++ programmers, a lot of
unsystematic C language elements are included in Java:
side effect expressions: x = i++ - (--j) +x
meaningless keywords: ‘static’ ...
Example: definition of a constant
CONST Num =100;
static final int Num = 100;
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Problems of Java as the first programming language (5)
Students do not learn the pointer (extremely
important concept) as a special data structure
like in C, C++, Pascal, Modula-2 (e.g. to
implement connected lists, trees ...)
Instead of it, in Java pointers are “simulated”
by the class concept (object references) –
which can make confusion for first year
students
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Problems of Java as the first programming language (6)
Other conventional data structures are
missing:
record / structure
“usual” arrays
union
enumeration
set / subset
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Problems of Java as the first programming language (6)
Array “missing” – An example:
If we have an array of type T1 and array of
type T2 (regarded as subclass of T1) - a
kind of covariance.
The pleasant consequence: array values of a subclass can be
assigned to array variables or parameters of a superclass.
The unpleasant consequence: it may lead to unexpected runtime errors, if an array variable has the run-time type of a
subclass (via an assignment as above) then it becomes
incompatible with the superclass or with other subclasses of the
same superclass (undetectable for the compiler).
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Problems of Java as the first programming language (6)
Array “missing” – An example:
public class person {
// a person has
String name;
// a name
void display() {…}…
// a display method
} // person
public class student extends person person {
// student is a subclass of person
int matrNr;
// a student has additional number
void display() {…}…
// and an overridden display method
} // student
…
public static void main (String argv[] ) {
person[] persons = new person [3]
//array of persons
student[] students = new student [3]
//array of students
…
students[1] = new student(“Paul”, 2);
persons = students;
// persons run-time type becomes array of students
persons[1] = new person(“John”)
// leads to ArrayStoreException
} // main
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Problems of Java as the first programming language (7)
The Java API:
It is not easy for beginners to cope with the big
diversity of standard classes in the library.
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Problems of Java as a first programming language (8)
OO programming is based on the concepts of
object (unit of hidden data + visible access operations)
class (a framework of similar objects – an instance of a class is an
object)
Java classes allow not only OOP but also a lot of other kinds
of software modules:
Classes which are completely in correspondence with OOP
Simpler constructs, e.g. implementation of quite ordinary
algorithmic elements (collections of input/output procedures)
This multi-functional use of the Java class concept is not easy
to comprehend by the students.
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Problems of Java as a first programming language (8) –
in other words:
Java is called to be an OO language
The Java class construct is claimed to support
objects, above all
However, in real Java programs, classes are not only
used to implement objects
Methodological challenge in lectures
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Conclusions: Java as the first programming
language at HU
Was necessary at HU: students motivation, OO from
the very beginning, preknowledge of the beginners
…
Has disadvantages: class is no abstraction, missing
data types, bad C constructs included …
Requires methodological concepts:
Part I:
Part II:
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Conclusions: Java as the first programming language at
DMI – Novi Sad?
Students motivation and preknowledge are in great
discrepancy …
Has disadvantages: class is no abstraction, missing data types,
bad C constructs included, not good for educational purposes
…
Teaching Java as a part of Programming languages course (II
year)
Still there are a lot of Universities which use some other more
educational languages (Modula, Pascal, Eiffel, SmallTalk, …)
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THANK YOU VERY MUCH
FOR ATTENTION
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