1. CSC3170 Introduction to Database Systems
Tutorial 6
Java
CSC3170 Introduction to Database Systems

2. Outline Basic Object-Oriented programming concept (OO Concept)
Java basic
Useful API (for project)
Compile and Run
Useful link and reference

3. OO Concept Object-Oriented programming Object Class
It uses objects and their interactions to design computer program.
Object
Object is used to describe an entity in the real world.
Class
A description of a set of objects that share the same attributes, operations, relationships, and semantics.

4. OO Concept -- Object Real world entity E.g. A student OOP State
Behavior
E.g. A student
Student ID, name, major, ……, etc.
Self-introduction, ..., etc.
OOP
instance variable
methods
Alice
Self-introduction
CSC
state
method
object
SID
Major
Name

5. OO Concept -- Object Self-introduction
C: Self_Intro(Alice); function
OOP: Alice.Self_Intro(); ----method
Object = related data + function
state
method

6. OO Concept -- Class A class is a template of an object Student
Self-introduction
state
method
object
SID
Major
Name

7. OO Concept -- Class They are all instances of class “Student”
Self-introduction
SID
Major
Name
Alice
CEG
James
CSC
Rose
IEE
Class “Student”
Object “Alice”
Object “James”
Object “Rose”

8. OO Concept -- Class Instance variables Instance methods
values are independent of instances
Instance methods
Can access only after created the instance
the output may vary due to the differences of instance variables

9. OO Concept -- Class Class variable Class methods
All instances share a single copy
Class methods
Cannot access the instance variables and instance methods
 Student.name
 Student.self_intro()
 Student.classMethods()

10. OO Concept – features Inheritance Abstraction Encapsulation
Each subclass inherits all variables and methods of its superclass.
Abstraction
Simply complex reality.
Encapsulation
The values of variables of an object are private.
Polymorphism
Allows the objects of different types respond to the method call of the same name.

11. Java basic – Hello World
//helloworld.c #include <stdio.h> int main(int argc, char * argv[]){ /* print “Hello World!” */ printf("Hello World!\n"); return 0; } C
//HelloWorld.java import java.io.*; class HelloWorld { public static void main(String[] args) { /* print “Hello World!” */ System.out.println("Hello World!"); }
JAVA

12. Java basic – Hello World
//helloworld.c #include <stdio.h> int main(int argc, char * argv[]){ /* print “Hello World!” */ printf("Hello World!\n"); return 0; } C
//HelloWorld.java import java.io.*; class HelloWorld { public static void main(String[] args) { /* print “Hello World!” */ System.out.println("Hello World!"); }
JAVA

13. Java basic – Hello World
Comment: the same with C (“//” and “/*…*/”)
#include <stdio.h> → import java.io.*;
a huge number of (standard) packages ready for use
Define a new class called “HelloWorld”
Define the “main” method in class “HelloWorld”

14. Java basic – Hello World
//import java.io.*; //not required for console output
class HelloWorld { /* print “Hello World!” */
public static void main(String[] args) {
System.out.println("Hello World!"); }
visibility
modifiers
return type
method name
parameter list
Visibility modifier
public, protected, private
“static” modifier
static class variable/method
Return type
void, int, double, char, boolean, <Array>, <Object>, <Interface>
Method name
Parameter list
Primitives: pass-by-value
Reference Types: “pass-by-reference”

15. Java basic -- Similar to C
Data Types
short, int, long, float, double
Operators
+, -, *, /, %, ++, --, >, >=, <, <=, ==, !=, &&, ||, !, &, |, >>, <<, ……

16. Java basic -- Similar to C
Control Flows (Selection)
if (<expression>) {
<statement(s)>
} else { }
switch (<expression>) {
case <constant>: <statement(s)>
break;
default: <statement(s)> }

17. Java basic -- Similar to C
Control Flows (iteration)
while(<expression>) {
<statement(s)> }
do {
<statement(s)>
} while (<expression>);
for(<initialization>; <termination>; <increment>){
<statement(s)> }

18. Java basic -- Different from C
External Dependencies
#include <header.h>  import package.*;
Data Types
char  byte (an 8-bit integer)
char  char (a character, e.g. ‘c’)
int  boolean (e.g. true / false)
int  int (a 32-bit integer)
char string[20] = “C Program”; /* an array */
 String string = “Java”; //an object
int array[8];
 int[] array = new int[8];//an object

19. Java basic -- Different from C
Operators
new
Object obj = new Object();
Student student = new Student();
instanceof
(student instanceof Student) = true
(obj instanceof Student) = false
(anything instanceof Object) = true
There is no pointers, no “alloc” in java.
System will manage the memory. We need not delete instances.

20. Java basic -- Different from C
To invoke the Java Program:
Then the argument array:
args[0] = “Peter”
args[1] = “Paul”
args[2] = “Mary”
args.length = 3
For C program:
Then, the argument array:
argv[0] = “hello_word”
argv[1] = “Peter”
argv[2] = “Paul”
argv[3] = “Mary”
argc = 4
java HelloWorld Peter Paul Mary
hello_world Peter Paul Mary

21. Java basic -- First Java Program
Model your application with objects
Design the states and behaviors of each object
Define a class for each type of object
Implement the states (with instance variables) and behaviors (with methods)
Write the main method to create objects and start the object interactions

22. Java basic -- First Java Program
class Student {
public static int NoOfStudents = 0;
public String SID;
public String Name;
public String Major;
//constructor (create an object / instance)
public Student(String SID, String Name, String Major){
NoOfStudents++;
this.SID = SID;
this.Name = Name;
this.Major = Major; }
public void Self_Intro() {
System.out.println(“Student ID:” + this.SID);
System.out.println(“Name:”+this.Name);
System.out.println(“Major:”+this.Major);
Student
Self_Intro
SID
Major
Name

23. Java basic -- First Java Program
class Student {
public static int NoOfStudents = 0;
public String SID;
public String Name;
public String Major;
//constructor (create an object / instance)
public Student(String SID, String Name, String Major){
NoOfStudents++;
this.SID = SID;
this.Name = Name;
this.Major = Major; }
public void Self_Intro() {
System.out.println(“Student ID:”+this.SID);
System.out.println(“Name:”+this.Name);
System.out.println(“Major:”+this.Major);
If you make everything “public”, everyone can change your “state”, So …
private String SID;
public String getStudentID() {
return SID; }
Now, only you can change your status and others can just see it but cannot modify it.

24. Java basic -- First Java Program
//Defining the class Student
class Student {
//class variable
private static int NoOfStudents = 0;
//instance variables
private String SID;
private String Name;
private String Major;
//constructor
public Student(String SID, String Name, String Major) {
NoOfStudents++;
this. SID = SID;
this. Name = Name;
this. Major = Major; }
//class method
public static int getNoOfStudents() {
return NoOfStudents;
//instance methods
public String getStudentID() {
return SID; }
public String getName() {
return Name;
public String getMajor() {
return Major;
public void Self_Intro() {
System.out.println(“Student ID:”+this.SID);
System.out.println(“Name:”+this.Name);
System.out.println(“Major:”+this.Major);

25. Java basic -- First Java Program
Model your application with objects
Design the states and behaviors of each object
Define a class for each type of object
Implement the states (with instance variables) and behaviors (with methods)
Write the main method to create objects and start the object interactions

26. Java basic -- First Java Program
class FirstClass { public static void main(String[] args) { Student alice, james, rose; alice = new Student(“ ", "Alice", “CEG"); james = new Student(“ ", “James", “CSC"); rose = new Student(“ ", “Rose", “IEE"); System.out.println(“Prof. Wong:”+alice.getStudentID()); alice.Self_Intro(); System.out.println (“Prof. Wong :”+ james.getStudentID()); james.Self_Intro(); System.out.println (“Prof. Wong :”+ rose.getStudentID()); rose.Self_Intro(); }

27. Java basic – toString()
public void Self_Intro() { System.out.println(“Student ID:”+this.SID); System.out.println(“Name:”+this.Name); System.out.println(“Major:”+this.Major); }
System.out.println(alice);
public String toString() {
return “Student ID:”+this.SID+”\n”+ “Name:”+this.Name+”\n”+ “Major:”+this.Major; }

28. Java basic – java IO Standard Output System.out.print[ln]()
can accept boolean, char, char[], double, float, int, long, Object, and String

29. Java basic – java IO Standard Input import java.io.*;
BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
To read string
str = in.readLine(); //Read a line
char c = in.read(); //Read a char
To read numbers
read String then convert to appropriate type using
Integer.parseInt(), Double.parseDouble(), …

30. Java basic – java IO File Input
BufferedReader inFile = new BufferedReader(new FileReader(new File(“filename”)));

31. Java basic –Exception Handling
Exception provides a smart way to handle “exceptional event”
An appropriate “exception handler” takes over when exception is thrown
You can also throw or re-throw an exception if you don’t know how to handle.
try {
<statement(s)>
} catch (<exception type> <name>) {
} finally {
/* this will be executed after normal execution
or execution of an exception handler */ }

32. Useful API public String[] split(String regex)
Splits this string (i.e. the string that invokes the split() method) around matches of the given regular expression
Example
String str = "boo:and:foo";
String[] result;
result = str.split(":");
System.out.println("(1)" + result[0]);
System.out.println("(2)" + result[1]);
System.out.println("(3)" + result[2]);
boo
and
foo
/48

33. Useful API public boolean equals(Object anObject) Compare Strings
Example
Don’t use == for String Comparison
if(str.equals("CSCI3170")) { … }

34. Compile and Run Java uses an interpreter to run the program
Add JAVA_HOME to Environment Variables with the path of JDK6 like C:\Program Files\Java\jdk1.6.0_24

35. Compile and Run
Add %JAVA_HOME%\bin;%JAVA_HOME% in Path

36. Compile and Run Java Compiler javac Java Interpreter java
Compile your source file(s)
Usage: javac <source file(s)>
E.g. javac Student.java, javac *.java
Java Interpreter java
Run your Java program
Usage: java <class file>
E.g. java Student
No “.java” / “.class” at the end

37. IDE – NetBeans
Netbeans is a fully-featured, free and open-source Java IDE written completely in Java
You can download from:

38. Useful Reference The Java Tutorial Java APIs
Java APIs
CSE Summer Preparatory Course
Free Electronic Book: Thinking in Java, 3rd Edition

39. Q&A