Java Technicalities

Java Technicalities
From a C/C++ Programmer’s View

yen3

Dept. of Computer Science and Information Engineering, Chang Gung University

April 15, 2009

. . . . . .

Java Technicalities 1/58

Introduction About

About Author
Computer Science Student
Blog: No title, no thinking, no meaning
E-mail: yen3rc gmail

C, C++, Java, Haskell, LTEX
A

. . . . . .


Introduction Outline

Introduction
About
Introduction
Technicalities
Type
Class and Object
Generic in Java (igonred)
Exception
Library and Programming
String
Container and HashTable
Java I/O
JDBC — Java Database Connectivity
Conclusion
Conclusion
Reference . . . . . .



About Slide

Josh Ko (Joshsoft)
XD
The slide is made by XELTEX and Beamer. XD
A

The Color Theme designed by Josh Ko uses Oxford brand colors1 .

1
http://www.ox.ac.uk/staﬀ/branding toolkit/the brand colours/index.html
. . . . . .



Something About Guang-Wu Chen’s Requirement
He hopes you understand the following topics.
String (all kinds of string/character processing stuﬀ)
StringTokenizer
Hashtable (or other containers such as Vector, etc.)
JDBC related ones, including Connector, Statement, ResultSet.
I/O classes, of course.

. . . . . .


Introduction Introduction

But ...
XD
XD

. . . . . .



But ...
XD
XD

Josh Ko and yen3’s Talking
yen3: Java ...Orz
Josh Ko: XD
yen3: Java Functional Programming XD
Josh Ko: , Java OO XD

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Everything is an Object.
Thinking in Java 4/e

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Programming
By Compiler
Compiled Programming language
Interpreted Programming language (Script Programming Language)
By Machine
Imperative Programming (Turing Machine)
Functional Programming (λ-calculus)
By Model
Procedural Programming
Object-Based Programming (Abstract Data Type)
Object-Oriented Programming
Generic Programming
. . . . . .



TIOBE Programming Community Index for March 2009

. . . . . .



About Java
James Gosling, 1995, Sun Microsystems
a pure Object-Oriented Programming Language
Everything is an object.
Java Virtual Machine and Just-In-Time Compiler XD
Java SE, Java EE, Java ME
The language has already been developed for over 10 years and
become a complete programming language.
So, What do we know from Java ?

. . . . . .


Technicalities Type

Type
Java has two different types.
primitive type: int, char, double, balabala
pointer type: class type(user-defined type)
We know that Java doesn’t have “pointers”
Java has “new”, but no “delete” keyword.
What is Garbage Collection?
What is Java’s memory management mechanism? (It’s an important
factor about Java’s program efficiency.)

. . . . . .


Technicalities Type

String Type
String has build-in type’s interface with pointer type’s
implementation.
String vs. StringBuffer2
What does the language do in background?
Let’s talk about an example.

2
In Java, StringBuilder provides an API compatible with StringBuﬀer, but with no
guarantee of synchronization. . . . . . .


Technicalities Type

Type-Casting
Java is strongly-typed programming language.
void* vs. java.lang.Object
In Java, every class inherits from java.lang.Object. It means we
can cast an object to java.lang.Object type and cast again to
other arbitrary class type .
Compiler doesn’t check the situation because it seems legal from the
syntactical perspective.
You have to check the situation by yourself.

. . . . . .


Technicalities Class and Object

Thinking about The Problems
What is a “type”? A Type just like requirement.3 (in Functional
Programming)
What is a “object”?
OO is claimed to be closer to human thoughts. However, is it true ?
Object vs java.lang.Object
Why doesn’t Java support “Operator Overloading”?
“Operator Overloading is syntax sugar. You don’t know how eﬀicient
you cost in using.”

3
Think about “Rules” . . . . . .



Class and Object
A Class has ...
data member (Data) – Record States
member function(Method)
A Class has three modes
public – interface
private – implements
protected – for some reasons XD
We have to pay attention to two keywords, but the slide doesn’t mention.
static
final

. . . . . .



Class
There are several kinds of classes.
Normal Class – There’s nothing to say. XD
Interface – Think about multiple-inheritance.
anonymous Class – Think about the relationship about function
pointer and call-back function.

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Back to C — Function Pointer
Von Neumann’s Model says program can be saved in memory.
If we ruled the function’s interface, we can show diﬀerence
functionality by replacing functions rely on function pointer.

For Example: C’ stdlib.h — qsort() protype

void qsort(void* base, size_t n, size_t size,
int (*cmp)(const void*, const void*));
/* function pointer */

. . . . . .



Back to C++ — Function Object
The most diﬀerence between Function Object and Function Pointer is
Function Object has own states(variable).
Implementation: Class with Operator Overloading “()”
If we implemented function object with template. It stars the Generic
Programming’s ﬁrst step.

For Example: C++ — Function Object

template<typename T> class Less{
public:
bool operator()(const T& x, const T& y){ return x < y;}
}

. . . . . .



λ Function (Lambda Function)
base on lambda-expressions from Functional Programming,.
no side-eﬀect function.
an unnamed function for temporary uses
Haskell n´ive support
a
C++’s support: Boost::lambda

For Example: C++ — Boost::lambda

std::sort(v.begin(), v.end(),
std::greater<iterator_traits(v.begin())::value_type>());
std::sort(v.begin(), v.end(), *_1 > *_2);

. . . . . .



Call-Back Function — Anonymous Class with Interface
What is “Call-Back Function”?
How does JavaScript support the Call-Back Function?
Class-Based vs Prototype-Based
Java uses anonymous class and interface(Runnable) to support
call-back property.

For Example: Java — anonymous class with interface

Thread newTask = new Thread(new Runnable(){
public void run(){ System.out.println("Hello World!"); }});

. . . . . .



Interface and Abstract Class
interface and abstract are keywords.
Interface and abstract classes provide a more structured way to
separate interface from implementation.
In begin, we always have no idea to use them.
It’s show time to use “Refactoring”.
We can extract to super class, abstract class, or interface from the
same functionality classes.
Button-Up Design vs Top-Down Design

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Object-Oriented Class
For eﬀicient reason, C++ default member function mode is
non-virtual, but Java is not.
Please read the relational books to get more details about Java’s
Class.
The feature is implemented by function pointer table.
Think about the relation of RTTI and function pointer table.
How to Design Class? Traditional OO Design vs eXtreme
Programming4

4
We will discuss the issue next week. . . . . . .


Technicalities Generic in Java (igonred)

Generic in Java
Let’s ignore the topic.
We can discuss the topic if we have a basic knowledge for C++
Generic Programming.
C++’s STL is made from some Functional Programming concepts.
Java’s Generic is made by Java OO method.
In fact, Java’s Generic is still a OO paradigm.
You can play the paradigm using Haskell. It’s more interesting than
C++ and Java. XD

. . . . . .


Technicalities Exception

Exception
What is a “Exception”?
“GOTO Considered Harmful.”5
Think about the relation between “goto” and “exceptions”.
We have to know program execute the exception block means low
eﬀiciency.
But we couldn’t ignore writing exception when using some library(ex:
I/O, Socket, Thread)

5
Edsger W. Dijkstra, Turing Award 1972 . . . . . .



Library
Muti-Threading Programming – java.util.concurrent.*
GUI Programming – javax.swing.*
Socket Programming – java.net.*
Generic Container – java.util.* (just for some classes) 6

I/O – java.io.* (It is a good OO design example.
balabala
Don’t forget gwchen’s requirements. XD

6
In C++, Generic Container is more interesting than Java.
. . . . . .



How to ﬁnd Java Document ?
Please have a book named “Thinking in Java 4/e”. XD
Google Keyword –
“your keywords site:http://java.sun.com/javase/6/docs/”
Eclipse code completes
Google XD

. . . . . .


Library and Programming String

What is a String?
What is a “char”? What is a “string” ?
What’s diﬀerence between “char array” and “string” ?
char’s size is 1 byte.
string’s element is not always using 1 byte for saving information.
Maybe using 2 bytes, or ...
Java’s String uses UTF-8 as default encoding.

. . . . . .



String method

charAt & indexOf
isEmpty
startsWith & endsWith
getBytes & getChars
subString
toCharArray
contains
toLowerCase & toUpperCase
replace & replaceAll &
format
replaceFirst
trim
matchs

. . . . . .



java.util.StringTokenizer
http://java.sun.com/javase/6/docs/api/java/util/StringTokenizer.html
It can break a string into tokens.
If you want to complexing method for separating string, you can using
“Regular Expression” and java.lang.String.split().

. . . . . .



Example: java.util.StringTokenizer

For Example: evaluate the sum of numbers

String s="123 456 789";
StringTokenizer token = new StringTokenizer(s, " ");

int sum=0;
while(token.hasMoreTokens()){
sum += Integer.parseInt(token.nextToken());
}
System.out.println("The sum is: " + sum + "n");

. . . . . .



Example: java.lang.String.split()
Attention: the argument using “Regular Expression”.
For Example: evaluate the sum of numbers

String s = "123 456 789";
String[] split = s.split(" ");

int sum=0;
for(int i=0;i<split.length;i++){
sum += Integer.parseInt(split[i]);
}
System.out.println("The sum is: " + sum + "n");

. . . . . .


Library and Programming Container and HashTable

Java Container
In Java 1.0/1.1, Java uses “Object Container”, but not suggests using
for now.
Java uses “Generic Container” instead of “Object Container” in Java
1.4 and after. Why does Java do?
Please ﬁrst consider “Array” unless you have enough reasons to use
Java Container.
And you can’t use primitive type in Generic Container, please use
“type wrapper class” instead of “primitive type”.
For example: type wrapper class

List<int> u = new ArrayList<int>; // wrong
List<Integer> u = new ArrayList<Integer>; // right

. . . . . .



Class Hierarchy Tree
java.util.Arrays
java.util.Collection<E>
java.util.List<E>
java.util.Queue<E>
java.util.Deque<E>
java.util.Set<E>
java.util.SortedSet<E>
java.util.Map<K, V>
java.util.SortedMap<K, V>
java.util.Dictionary<K, V>
java.util.Hashtable<K, V>
java.util.AbstractMap<K, V>
java.util.HashMap<K, V>
java.util.LinkedHashMap<K, V>
java.util.TreeMap<K, V>
. . . . . .



Vector — java.util.List<E>
java.util.List<E> is an interface class.
The Most frequently using List is java.util.List.ArrayList
In interface, like C++’s std::vector<typename T>
add() vs. push back()
get() vs. operator[]
size() vs. size()
Although “Vector<E>” can be used, but Java’s doc suggests using
“List” instead of “Vector”.

. . . . . .



Example: java.util.List<E>

For Example: Count words of a ﬁle (1–2)

public int fileWordCount(String filename){
try{
List<String> fileList = readFile(filename);
int totalWords =0;
for(int i=0;i<fileList.size();i++){
totalWords += fileList.get(i).split(" ").length;
}
return totalWords;
}
catch(Exception e){
System.out.println(e);
}
return -1;
}
. . . . . .



Example: java.util.List<E> (2–2)

For Example: Count words of a ﬁle

public ArrayList<String> readFile(String filename) throws IOException{
try{
ArrayList<String> u = new ArrayList<String>();
BufferedReader in = new BufferedReader(new FileReader(filename));
String readLine = null;
while((readLine = in.readLine())!=null){
u.add(readLine);
}
in.close();
if(u.isEmpty()) return null;
else return u;
}
catch(FileNotFoundException e){
System.out.println(e);
}
return null;
}

. . . . . .



HashTable — java.util.HashMap<K, V>
HashMap can support the same functionality as HashTable.
Please use java.util.HashMap<K, V> instead of
java.util.HashTable<K, V>
K is key, V is Value
If you want use some class as a key, please check the class override
“Object.hashCode()” and “Object.equals()”.

. . . . . .



Example: HashMap

For Example: HashMap list all entries

HashMap<String, Integer> nameAge =
new HashMap<String, Integer>();
nameAge.put("John", 15); nameAge.put("Mary", 17);

Set<Map.Entry<String, Integer>> set = nameAge.entrySet();
Iterator<Map.Entry<String, Integer>> iter = set.iterator();
while(iter.hasNext()){
Map.Entry<String, Integer> e = iter.next();
System.out.println(e.getKey() + " " + e.getValue());
}

. . . . . .


Library and Programming Java I/O

Java I/O
What is a “Stream”?
In Unix/Unix-like, everything is a ﬁle.
Java I/O Library is a pure OO paradigm example, and C++ is too.
You can get an overview by java.io.* hierarchy tree.7 It will helps
you to understand how to write I/O codes.

7
http://java.sun.com/j2se/1.4.2/docs/api/java/io/package-tree.html
. . . . . .



Java I/O: Two Methods
Java has “InputStream/ OutputStream”, “Reader/ Writer”
InputStream/ OutputStream read 1 byte at a time.
Reader/ Writer read a char at a time.8
Reader/ Writer default encoding is UTF8.
Recall: Java’s String type default encoding is UTF8.
Which can be used depends on your source.

8
a char can be 1 byte, 2 bytes, ... . . . . . .



Java I/O: InputStream/ OutputStream
InputStream/ OutputStream
ByteArrayInputStream/ ByteArrayOutputStream
— for String.getBytes(); (1 byte string)
FileInputStream/ FileOutputStream
— for files
Socket.getInputStream()/ Sokcet.getOutputStream()
— for Socket
Process.getInputStream()/ Process.getOutputStream()
— for Process Control

You can use the above to adapt to the following
BufferedInputStream/ BufferedOutputStream
— Support readLine()
DataInputStream/ DataOutputStream
— Support readInt() ... . . . . . .



Java I/O: Reader/Writer
Reader/ Writer
StringReader/ StringWriter — for a String.
FileReader/ FileWriter — for a file.
CharArrayReader/ CharArrayWriter – for memory

You can use the above to adapt to the following
BufferedReader/ BufferedWriter — Support readLine()
Scanner/ not support

. . . . . .



Java I/O: Others
The Bridge between InputStream/ OutputStream and Reader/ Writer
InputStreamReader/ OutputStreamWriter
— Stream translate to Reader/Writer

For Example: Socket

BufferedReader br = new BufferedReader(
new InputStreamReader(Socket.getInputStream()));

The following is not maintained.
RandomAccessFile
ObjectInputStream/ ObjectOutputStream
Java.nio (New I/O) . . . . . .



Example: evaluate the sum

For Example: evaluate the sum

public int evaluateSumByScanner(String s){
StringReader sr = new StringReader(s);
Scanner scanner = new Scanner(sr);

int sum = 0;
while(scanner.hasNext()){
sum += scanner.nextInt();
}
sr.close();
return sum;
}
. . . . . .



Socket Programming
Socket Programming is the same as writing to files because we
consider socket as a file stream.
use “Buffered I/O” (ex: class java.io.BufferedWriter, class
java.io.BufferedReader)
We have to be care about the message’s format.(fixed format or XML
formt)
Please don’t use “n” as a message’s end!
Please remember “Base64” format when you send binary messages.9
Reference: yen3’s blog – File I/O (1) ,
(2) Binary File, (3) XML

9
http://en.wikipedia.org/wiki/Base64 . . . . . .



Socket Programming
Client – java.net.Socket
Server – java.net.ServerSocket
Usually, We use Socket Programming together with Multi-threading
Programming in Server.
Don’t forget “ThreadPool”(java.util.concurrent.Executors)

. . . . . .


Library and Programming JDBC — Java Database Connectivity

JDBC — Java Database Connectivity
an API for the Java programming language that deﬁnes how a client
may access a database.
It provides methods for querying and updating data in a database.
JDBC is oriented towards relational databases.
Reference: Wiki: Java Database Connectivity
Reference: caterpillar: Java (JDBC)
How To use?

. . . . . .



JDBC Example: MySQL
Please install MySQL. XD
Please download MySQL Connector/J 5.1, the offical JDBC driver,
you will get a “jar” file.

In Eclipse, press “Add External JARs...”, choose the file you
downloaded.
Have fun!

. . . . . .



JDBC Example: Java and MySQL

For Example: List a table

public void testMySQL(){
String driver = "com.mysql.jdbc.Driver";
String serverName = "localhost";
String databaseName = "information_schema";
String tableName = "TABLES";
String user = "yourname";
String password = "yourpassword";
String url = "jdbc:mysql://"+ serverName +"/" + databaseName;

. . . . . .



JDBC Example: Java and MySQL

For Example: List a table

try {
Class.forName(driver);
Connection conn = (Connection) DriverManager.getConnection(url, user, password);
Statement stmt = (Statement) conn.createStatement();
ResultSet result = stmt.executeQuery("SELECT * FROM" + " " + tableName);
while (result.next()) {
int numColumns = result.getMetaData().getColumnCount();
for (int i = 1; i <= numColumns; i++) {
System.out.println("COLUMN " + i + " = "
+ result.getObject(i));
}
}
conn.close();
}
catch(ClassNotFoundException e) {
System.out.println("Can not find JDBC driver");
}
catch (SQLException e) {
e.printStackTrace();
}
}
. . . . . .


Conclusion Conclusion

Conclusion
We go through Java from diﬀerent parts, especially from C/C++.
We go through some Java Library ... There are a lot of examples.
Please review it. XD
Java is a noun-kingdom XDXD. (What do you think about when
seeing “ArrayIndexOutOfBoundsException” ﬁrst time?)
Please love “Eclipse IDE” when developing Java programs. XD
Let’s expect the interesting issue next week . XD

. . . . . .


Conclusion Conclusion

Do you have any problem ?
I am glad you have listened the slides from start to now. XD

. . . . . .


Conclusion Reference

Reference — Website
Java SE Documentation –
http://java.sun.com/javase/downloads/index.jsp
Eclipse.org – http://www.eclipse.org
– http://caterpillar.onlyfun.net/Gossip/

C++ Boost Library – http://www.boost.org
SGI STL – http://www.sgi.com/tech/stl/
TIOBE Software: Tiobe Index –
http://www.tiobe.com/index.php/content/paperinfo/tpci/index.html

. . . . . .



Reference — Java
Thinking in Java 4/e, Bruce Eckel, ISBN: 0131872486
The Java Programming Language 4/e, Ken Arnold, James Gosling,
David Holmes , ISBN: 0321349806
Eﬀective Java 2/e, Joshua Bloch, ISBN: 0321356683
Practical Java(TM) Programming Language Guide, Peter Haggar,
ISBN: 0201616467
The Art of Java, Herbert Schildt, James Holmes, ISBN: 0072229713
Java Network Programming 3/e, Elliotte Rusty Harold, ISBN:
0596007213
Java Swing 2/e, James Elliott, Robert Eckstein, Marc Loy, David
Wood, Brian Cole, ISBN: 0596004087

. . . . . .



Reference — Object Oriented Analysis/ Design/ Programming
Object-Oriented Analysis and Design with Applications 3/e, Grady
Booch, Robert A. Maksimchuk, Michael W. Engel, Bobbi J. Young,
ISBN: 020189551
Design Patterns: Elements of Reusable Object-Oriented Software,
Erich Gamma, Richard Helm, Ralph Johnson, John Vlissides, ISBN:
0201663612
Refactoring: Improving the Design of Existing Code, Martin Fowler,
Kent Beck, John Brant, William Opdyke, don Roberts, ISBN:
0201485672
Refactroing to Pattens, Joshua Kerievsky, ISBN: 0321213351
Agile Software Development, Principles, Patterns, and Practices,
Robert C. Martin
. . . . . .



Reference — C/C++ and Other
Real World Haskell, Bryan O’Sullivan, John Goerzen, Don Stewart,
ISBN: 0596514980
The C++ Programming Language 3/e, Bjarne Stroustrup, ISBN:
0201700735
The C Programming Language 2/e, Brian W. Kernighan, Dennis M.
Ritchie, ISBN: 0131193716
C++ Primer 4/e, Stanley B. Lippman, Josée Lajoie, and Barbara E.
Moo, ISBN: 0201721481
Eﬀective C++ 3/e: 55 Speciﬁc Ways to Improve Your Programs and
Designs, Scott Meyers, ISBN: 0321334876
Generic Programming and the STL: Using and Extending the C++
Standard Template Library, Matthew H. Austern, ISBN: 0201309564
. . . . . .



Appendix A: How to get a html String

For Example: How to get a html String

public String getHtmlString(String inputUrl){
try{
URLConnection url = (new URL(inputUrl)).openConnection();
BufferedReader br = new BufferedReader(
new InputStreamReader(url.getInputStream()));
int length=-1;
StringBuffer sb = new StringBuffer();
char[] temp = new char[1024];
while((length=br.read(temp, 0, 1024))!= -1){
sb.append(temp, 0, length);
}
br.close();
return sb.toString();
}catch (MalformedURLException ex) {
System.err.println(inputUrl + "is not parseable URL");
}catch (IOException ex) {
System.err.println(ex);
}
return null;
} . . . . . .



Appendix B: How to write Java Program
Please install “Java Developer Kit(JDK)” and “Java Runtime
Environment”
Please set “PATH” and “CLASSPATH” in Windows.
You can download “Eclipse” as your default Java Develop IDE.
Have fun!

. . . . . .


Java Technicalities

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