| JAVA 2.0
Notes
Java is an Object-Oriented, multi-threaded programming language developed by Sun Microsystems in 1991. It is designed to be small, simple and portable. The popularity of the Java is due to 3 key elements powerful programming language, applets and rich set of significant object classes. Adv of Java
In Java development environment, there are two parts, a Java compiler and Java interpreter. Java compiler generates byte code and interpreter executes the Java program. Eventhough the bytecode is slow, it gives platform independent application. Java program is typed in and saved in a file with
extension .java. This file is compiled by javac. It creates a file with
.class extension. This is executed by Java file without extension. A simple
example for a Java program is
Example 1: class first { public static void main (String s[ ] ) { System.out.println("Welcome to Java ") ; } } It was saved in the file first.java and compiled by java first.java and executed by java first. Class declaration is done in the first line of the program by class classname Every java program has main( ) method, which was first executed. void keyword indicates that main( ) does not return any value. static indicates that main( ) is a class method and can be called without creating an object. public indicates the method is global.
Data types : int 32 short 16 -32768 to 32767 byte 8 -128 to 127 float 64 Characters char 16 0 to 63536 String Boolean : boolean true or false Character Escape Sequences \n \t \f \b \\ \’ \" \ddd \uxxxx
To declare a variable type variable=value,variable=value,…; To initialize a variable int a=10; String name="palani"; float sal=5400.50f;
Arrays: int arr [12] ; char carr[ ] = { ‘a’,’b’,’c’,’d’} ; int a[12][10] ; char name[10][10][10] ;
Type casting: When one type of data is assigned to be another type of variable, an automatic type conversion will take place. For example byte a=10; int c = a + 10; Here, a is converted to int automatically.
To manually convert a type use (type) value For example float f = (float) a/ float(b) ; if a, b are integers. Example 2: class cast { public static void main(String args[ ]) { byte a = 10, b = 20 ; int c = 15, d = 2 ; float f1 = c/d; // f1 is 7.0 float f2 = (float) c / (float) d ; // f2 is 7.5 c = b + 10 ; // b is automatically converted to int /* b = b + 10 ; Error : cannot assign int to byte */ b = (byte) (b + 10); System.out.println("f1 =" + f1 " + "f2 = " + f2 " + "c = " + c + "b = "+b); } }
Operators 1) Arithmetic - + - * / % 2) Relational - < > <= >= != 3) Logical - && || != 4) Assignment - = 5) Comparision - = = 6) Incre/Decrement - ++ -- 7) Bitwise operator - ~ & | ^ >> >>> << &= != ^= 8) Conditional - ? :
Comments : // Single line comment /* */ Multiline line comment /** */ Document line comment
They are divided into
If (condition) { set of statements1; } else { set of statments2 ; } Example 3: class if { public static void main(String a[ ]) { int a=5,b=10; if (a>b) System.out.println("A is big"); else System.out.println("B is big"); } } b) for for (var=value1; condition; iteration) { statements; }
Example 4: class for { public static void main(String a[ ]) { for(int a=0; a<10; a++) System.out.println("A is big"); } } c) while and do..while while(condition) do { { statements; statements; } } while(condition);
Example 5: class dowhile { public static void main(String a[ ]) { int a=5 ; { a--; } d) switch switch (expr) { case value1: statements1 ; break; case value2: statements2 ; break; : : case valuen: statementsn; break; default: statements ; }
Example 6: class switch { public static void main(String a[ ]) { int a=5 ; switch(a) case 0: } }
e) break, continue and exit break will transfer the control out of the loop,
in continue , the rest of the lines are ignored and loop continue after
the next iteration. The exit function will stop the program execution.
Classes The most important feature of the OOP is classes. A class defines the shape and behavior of an object and is a template for multiple object with similar features. It is a logical construct upon which the entire java language is built because it defines the shape and nature of the object. To create a class, a source file with the class keyword
in it, followed by a name and pair of curly braces for the body.
access class classname { type instance-variable; type method(parameters) { body of method; } } Once class is created, an instance of class is created
by new keyword. The instance of class is used to access the variables
and methods that form part of the class. The dot operator is used to get
the value of the class variable (object.variable).
Instance Variable : Data is encapsulated in a class by declaring varables inside the class declaration. Variables declared in this scope are called as Instance variables. Class Variable : Class variables are global to class and all the instances of the class. To declare class variable static keyword is used. The access of class may be public, private, abstract
or final.
Methods Methods are functions that operate on instances of
classes in which they are defined. Method definition has four parts. They
are name of the method, return type , list of parameters and body of the
method.
returntype methodname (type arg1, type arg2,…) { Statements; }
To call a method methodname( ) or obj.methodname(para1, para2,…) ; An example for a class which has a class and method Example 7: class area { int len=10, bra=20; void calc( ) { int ara = len * bra; System.out.println("The area is " + ara); } public static void main(String a[ ]) { area a = new area( ); a.calc( ); } }
Access Specifiers: classes. Package : It is indicated by the lack of any access modifier in a declaration. Abstract : in abstract class without body, must be overridden by subclass. Static : It is automatically called when creating instance of class. this: The this keyword is used inside any instance method
to the current object.
Constructor A constructor method is a special kind of method
that determines how an object is initialized when created. They have the
same name as the class but do not have any return type. Consturctor can
also be overloaded.
Example 8: class cons { int I; int j; cons(int a, int b) { I=a; j=b; } void print( ) { cons c = new cons(10,10); c.print( ); } }
Garbage collection When no reference to object exits, the object no longer needed, the memory occupied by the object is reclaimed. This is called garbage collection. Java periodically does garbage collection. Finalizer : Finalizer method is the exact opposite of constructor method. They are called just before the object is garbage collected and its memory is reclaimed. All cleanup operations are performed in this method. protected void finalize( ) { } Methods overloading Methods overloading is creating different methods
with same name but with different parameters. This is the one type of creating
polymorphism
in Java
Example for method overloading and constructor overloading Example 9: Box( ) { int depth; int height; Box(int w, int d, int h) { Box(int a) { witdth = a; height = a; depth = a; } Box( ) { witdth = 1; height = 1; depth = 1; } void show( ) { System.out.println(width * height * depth); } void show(int a) { System.out.println("Height = " + h); System.out.println("Cube is " + (width * height * depth )) ; class boxdemo { public static void main(String args[ ]) Box b1 = new Box(3,4,5); Box b2 = new Box(5); b2.show( ); Method Overriding Method overriding is creating a method in the derived class that has the same name arguments as in the superclass. This new method hides the superclass method. Recursion Recursion is the process of defining something in terms of itself. A method that calls itself is said to be recursive. Example 10: class factorial { int fact(int n) { } class recurse { public static void main(String a[ ]) System.out.println("Fact of 3 is "+f.fact(3)); } }
Nested Class It is possible to nest a class definition within another and treat the nested class like any other method of that class. An inner class is a nested class whose instance exists within an instance of its enclosing class and has direct access to the instance members of its enclosing instance. class enclosingClass { class innserClass } Example : class outclass { int a =10; public void m1( ) { System.out.println("This is inner class method"); inclass in = new inclass( ); in.m2( ); } class inclass { public void m2( ) { System.out.println("This is inner class method"); System.out.println("a = "+ a); } } public static void main(String arg[ ]) { outclass out = new outclass( ); out.m1( ); } }
Inheritance is the method of creating new class based on the already existing class. The new class derived is called as sub class or derived class which has all features of the existing class and its own. The existing class is called as super class or base class. Adv : reusability of code, accessibility of variables and methods of the base class by the derived class. If the class is derived from more than one class
, then it is called as multiple inheritance. This is not available in Java.
To
overcome this problem use interface.
Method Overriding Whenever there are methods of the same name both
in the base class as well as in the derived class and if that method is
called by main, the method in the derived class is always executed. This
is called overriding. See example11.
Example 11: class A { void m( ) { } class B extends A { void m( ) // it will override super class's method { System.out.println ("This is sub class"); } }
Super Super has two forms. First it calls the superclass’s
constructor. The second is used to access a member of the superclass that
has been hidden by a member of a subclass.
Example 12: class A { int a = 10; void A(int k) { System.out.printn("k is " + k); } void m( ) { System.out.println("This is super class"); } } class B extends A { int a = 20; void m( ) // it will override super class's method { System.out.println("This is sub class"); } void call( ) { super(5); // to call super class's constructor m( ) ; // it will call the method in the derived class super.m( ); // to call super class's method int c = a ; int d = super.a ; // to assign super class's varaible. } class inh { public static void main(String args[ ]) { B ob = new B( ); }
Final
final int a = 40 final is used to create constant variable. b) final modifiers - to prevent overriding Final modifiers are those to which no further alteration can be made. We can not override the method using final Example 12: class A { final void meth( ) { System.out.println("this is the final method can not overridden"); } } class B extends A { void method( ) //this line will show error. System.out.println("Illegal"); } c) final class - to prevent inheirtance If the class is declared as final , we cannot inherit it. All methods in the final class are final final class A { } class B extends A // error cant subclass of A { }
Abstract Sometimes we will want to create a superclass that only defines a generalized form that will be shared by all of its subclasses, leaving it to each subclass to fill in the details. To declare abstract class abstract type name(parameters); We must override the abstract method. An abstract
class cannot be directly instantiated with the new operator. We cannot
declare abstract constructors or abstract static methods.
Example 13 : abstract class A { abstract void callme( ); void display( ) { System.out.println("This is example for abstract class"): } } class B { void callme( ) { System.out.println("B's implementation of callme"); } } class abst { public static void main(String a[]) { B b = new B( ); b.callme( ); b.disp( ); } } An exception is an abnormal condition or error that occurs during the execution of the program. Exception in java is handled by five keywords – try, catch, finally, throw and throws. The object class has a subclass called Throwable
to handle exception and errors, which has two subclasses Exception and
Error.The classes of exception are IOException and RuntimeExveption
The try and catch fixes the error and prevents the program from terminating abruptly. The finally block will be executed if no catch matches it and always executed. If you use try block, finnaly block or atleast one catch block should be used. If you don't want to use try and catch statements then use throws clause. The throws class is responsible to handle the different types of exceptions generated by the program. This clause usually contains a list of types of exceptions that are likely to occur in that program. The throw clause is used to call exception
explicitly. User defined exception can be called by throw clause. User
defined exception is created by extending the class Exception.
Examples for simple catch statements Example 14 : class exc4 { public static void main(String args[]) { try{ int a[5]; a[12]=33; } catch(ArrayIndexOutOfBoundsException a) { a[1]=33; } } Example multiple catch statements If you pass any arguments to main then, second error occur or division by zero will occur. finally is always called. Example 15: class except { static void proca(int v) { int k[4]; try { System.out.println(10/v); System.out.println("Inside proca"); K[10] =2; } catch(ArithmeticException e) { { finally { System.out.println("finaly Exceptin is caught"); } } public static void main(String a[]) { int l = a.length; proca(l); } }
Example to use throws clause. Example 16 : class ThrowsException { public static void main(String s[ ]) throws ArithmeticException int j = 40/0; System.out.println("This stt is not printed"); } }
Example for user defined exception Example 17 : class myexcep extends Exception { private int detail; myexcep(int a) { detail =a; } public String toString( ) { return "MyException"+detail; } } class exc11 { static void compute(int a) throws myexcep { System.out.println("called compute"+a); if (a>0) throw new myexcep(a); System.out.println("Normal exit"); } public static void main(String arg[]) { try{ compute(-1); compute(20); }catch(myexcep e) { System.out.println("My excep caught"+e); } } }
Some Unchecked runtime exceptions are ArithmeticException ArrayIndexOutOfBoundsException ClassCastException IndexOutOfBoundsException NullPointerException NumberFormatException SecurityException Java’s Built In exceptions are ClassNotFoundException CloneNotSupportedException IllegalAccessException
Package contains set of classes in order to ensure that class names are unique. Packages are container of classes used to keep the class name space compartmentalized.
Import packname.*; or particular class by Import packname.classname;
Example 18 : package pack; public class class1 { public static void greet( ) { System.out.println ("Hello"); } }
save above in file class1.java in the directory pack. Import pack.*; class importer { public static void main(String s[]) { class1.greet( ); } }
save it as importer.java in the previous to pack
directory and execute it.
If Java source file contain package, interface, classes then the order should be
An interface is a collection of abstract behavior that individual classes can implement. An interface consists of set of method collections. Using interface, you can specify what a class must do but not how it does it. All methods and final variables in interface must be public. Multithreading is not available in Java. To overcome this problem, interface is introduced. access interface name { type final-variable=value; access is either public or default. Example 19: public interface address { public void add(String add); class A implements address { public void add(String a) { System.out.println("Inside implemented method"); } public void name(String n) { System.out.println("Inside implemented method"); } void disp( ) { System.out.println("Method of class A");} public static void main(String a[ ]) { A a = new A( ); address interface"); a.name("swathi"); a.add("3,sivan koil st"); System.out.println("=============="); } }
Input int read( ) throws IOException final String readLine( ) throws IOException int n = System.out.read( ); String str = inData.readLine( ); Here DataInputStream inData = new DataInputStream (System.in); Output System.out.println( ); System.out.print( ); System.out.write (int byte); - console output
Reading and Writing files It throws IOException FileInputStream fin = new FileInputStream(filename); int fin.read( ) - to read a char from a file void fin.close( ) - to close a file FileOutputStream fout = new FileOutputStream(filename); void fout.write(int I); fout.close( );
String Methods : String s = new String( ); char chars[ ] { ‘a’, ‘b’, ‘c’); String s1 new String(chars); Int s.length( ) boolean s.equals(s1) String s.substring(int,int) ; char s.charAt(int); String toString(object); String s.replace(char,char); String s.trim( ); String s.toLowerCase( ); String s.toUpperCase( );
Thread A process is a program in a execution. A thread is a line of execution.
Two or more processes running concurrently in a computer is called multitasking.
The process can contain multiple threads to execute its different sections.
This is called multhreading. Using this, we can run different parts of
the programs at a time.
States of thread There are four states of thread. They are new, runnable, blocked
and dead The fig shows the states of the thread.
start( ) suspend( )/wait( ) / sleep( ) resume( ) stop( ) run( ) stop( )
Adv of thread:
b) creating the objects of the class Thread
{ }
Thread t = new Thread(this) ; Thread t = new Thread(this,"Demo thread’); Where this referes the Applet object. class c1 extends Thread { } Thread ThreadGroup ThreadGroup(String name) ThreadGroup(ThreadGroup ob,String name)
class thread1 implements Runnable { Thread t = new Thread(this,"test thread") ; System.out.println("Child thread : " + t) ; t.start( ) ; } public void run( ) { try{ for(int I=5; I>0; I--) { System.out.println("child thread"+I); Thread.sleep(500); } } catch(InterruptedException e) { } System.out.println("exiting child thread"); } public static void main(String g[ ]) { thread1 th = new thread1( ); try{ for(int j=5;j>0;j--) { } } catch (InterruptedException e) { } System.out.println("Main thread exiting …"); } } Creating Thread extends Thread class class thread2 extends Thread { thread2( ) { super("test thread") ; System.out.println("Child thread : " + this) ; start( ) ; } public void run( ) { try{ for(int I=5; I>0; I--) { System.out.println("child thread"+I); Thread.sleep(500); } } catch(InterruptedException e) { } System.out.println("exiting child thread"); } public static void main(String g[ ]) { new thread2( ); try{ for(int j=5;j>0;j--) { } } catch (InterruptedException e) { } System.out.println("Main thread exiting …"); } }
Runnable abstracts a unit of executable code. We can construct a thread on any object that implements Runnable. The thread methods are start( ), resume( ), sleep( ), suspend( ) , join( ) and toString( ) .
Synchronization Two or more threads accessing the same data simultaneously may lead to loss of data integrity. Java uses the concept of monitor. A monitor is an object, used as a mutually exclusive lock. Java offers interprocess communication through the use of wait( ), notify( ) and notifyall( ) methods of Object class and all are synchronized methods. Thread Priorities The usage of setPriority( ) and getPriority( ) methods are used to
set and get the priorities of thread respectively. The yield( ) method
enables provision of CPU’s time to threads with equal priority and prevents
monopolization of a single thread. The Thread has final variables declared
line – NORM_PRIORITY (5), MINIMUM_PRIORITY (1) and MAXIMUM_PRIORITY (10).
9. APPLET An applet is a dynamic and interactive program that can run inside Web page displayed by a Java-capable browser or applet viewer. All applets are subclasses of Applet. You should import java.applet and java.awt since all applets run in a window. Applet defines three interfaces Appletcontext, AppletStub and AudioClip. /* <Applet CODE="classname.class" WIDTH=400 HEIGHT=100> </APPLET> */
Applet extends java AWT class Panel, Panel extends Container which
extends Component.
The init( ) Method This method gets called as soon an applet is started. Initialization of all variables, creation of objects, setting of parameters, etc. can be done in this method. The start( ) method This method is executed after the init mehod. Also used to restart the applet that was stoped. The stop( ) method This method is used to halt the running of an applet. This method is called when a web browser leaves the HTML document containing the applet. The destroy( ) method This method is used to free the memory occupied by the variables
and objects initialized in the applet. Called by the browser just before
the applet is terminated.
The paint( ) method This method helps in drawing, writing and creating a colored background
or an image on to the applet. This method is called each time your applet’s
output must be redrawn. It has one parameter called Graphics.
The repaint( ) method This method is used in case an applet is to be repainted. The repaint
method calls update( ) method to clear screen and paint( ) method to redraw
the contents of the current frame.
resize (width, height) Resize the applet window showStatus (str) Displays the string in the status window of the applet
When starting the applet init, start, paint methods and when terminating stop and destroy methods are called. 9.a. The Graphics Class in java.awt package drawString(message,x,y);
drawLine (x1,y1,x2,y2); drawRect (x1,y1,width,height) drawRoundRect (x1,y1,width,height,width1,height1) draw3Drect (x1,y1,width,height,boolean) drawPolygon (xs,ys,pts) drawOval (x1,y1,width,height) drawArc (x1,y1,widht,height,angle1,angle2) fillRect (x1,y1,width,height) fillRoundRect (x1,y1,width,height,width1,height1) fillPloygon (xs,ys,pts) fillOval (x1,y1,width,height) fillArc (x1,y1,widht,height,angle1,angle2)
9.b. Font Class in java.awt package Font f = new Font ("fontname", format, size); Formats are Font.BOLD, Font.ITALIC, and Font.PLAIN g.setFont(f)
9.c. Color Class in java.awt package Color.grey, Color.green, Color.yellow, Color.pink,
Color.red, Color.blue, Color.magenta, Color.cyan
setColor (color) getColor (color) setBackground (color) getBackground (color) setForeground (color) getForeground (color)
9.d. Images
getImage (URL,string) drawImage (Image,x,y,imageObserver) to find URL getCodeBase ( ) can be used To create image createImage (width,height) getGraphics ( )
Clipping A technique by which the drawing area can be restricted to a small portion of the screen. Method is clipRect( ) clipRect(x1,y1,x2,y2);
Animation Animation is technique by the object is moved on
the screen In which the original image is clreared and placed in another
place.
9.e. Events Mouse Events methods
boolean mouseDown(event , x, y) boolean mouseDrag(event , x, y) boolean mouseEnter(event , x, y) boolean mouseExit(event , x, y) boolean mouseMove(event , x, y) boolean mouseUp(event , x, y) boolean mouseDown(event , x, y) boolean mouseDown(event , x, y)
KeyBoard Events boolean keyDown(event , x, y) boolean keyUp(event , x, y) Types of Event handling a)Low Level event Low level classes Low level event Listener ComponentEvent ComponentListener FocusEvent FocusListener KeyEvent KeyListener ContainerEvent ContainerListener MouseEvent MouseListener MouseMotionListener WindowEvent WindowListener InputEvent b) Semantic Events Low level classes Low level event Listener ActionEvent ActionListener AdjustmentEvent AdjustmentListener ItemEvent ItemListener TextEvent TextListener
Example: import java.awt.*; mport java.awt.event.*; import java.applet.*; public class mousetest extends Applet implements MouseListener { public void init( ) { addMouseListener(this); } public void mouseClicked(MouseEvent e) { showStatus("Mouse clicked at " + e.getX( ) +" , " + e.getY( )); } // Write above code for other mouse events } Each component class in the AWT has one addXXXListener( ) method for each event type. 9.f. ABSTRACT WINDOW TOOLKIT (AWT)
Button Button( ) setLabel(String) Button("label") getLabel( ) Label Label( ) getText( ) Label(String) setText(String) Label(String, int) getAlignment( ) SetAlignment(int) where Int is alignment. It may be Label.LEFT, Label.RIGHT,
Label.CENTER
Checkbox Checkbox( ) setLabel(string) Checkbox(String) getLabel( ) Checkbox(String,grp,boolean) setState(boolean) getLabel( ) Choice Choice( ) getItem(int) addItem(String) getItemcount( ) getSelectedItem( ) getSelectedIndex( ) TextComponent TextField( ) getText( ) TextField(String, int) setText(String) TextArea( ) TextArea(String, int, int) int represents rows and columns List List( ) getItem(int) int starts from 0 List(int,boolean) getItemCount( ) AddItem(String) select(int) getSelectedItem( ) Scrollbar Scrollbar( ) setValue(int) Scrollbar(orient, value, visible, min, max) getValue(
)
Layout Manger A set of classes used to position the components
in a container.
Flow Layout Lays components linewise from left to right FlowLayout( ) FlowLayout(align, hgap, vgap) Align – FlowLayout.LEFT, FlowLayout.RIGHT, FlowLayout..CENTER Grid Layout Position the components in the cellf of the grid. GridLayout(int rwo, int col) GridLayout( int rwo, int col, int hgap, int vgap) Border Layout Lays components relative to the edges of the container BorderLayout( ) BorderLayout(int hgap, int vgap) add("direction",item); direction may be NORTH, SOUTH,EAST , WEST or CENTER Insets(int, int, int, int) Used to give spacing around the container
Panel A panel class is a non-abstract, recursively nestable container. Panel( )
9.g. Frames, Menus and Dialogs Frame Inherited from Frame class Frame( ) Frame(String)
Methods setVisible(boolean) setSize(Dim) setLocation(int,int) getLocation( ) dispose() setTitle(String) getTitle( )
Menus
Menubar( ) Menu(String) MenuItem(String) CheckboxMenuItem(String) SetState(boolean) getState( ) menu.add(MenuItem) menubar.add(menu) Frame.setMenubar(menubar) Dialog Dialog(Frame,boolean) Dialog(Frame,String,boolean) setResizable(boolean) isModal( ) import java.awt.*; import java.awt.event.*; import java.applet.*; class fram extends Frame { String msg=" "; fram() { super("Menu Frame"); MenuBar mb = new MenuBar(); Menu m1 = new Menu("File"); Menu m2 = new Menu("Edit"); MenuItem mi1 = new MenuItem("Open"); MenuItem mi2 = new MenuItem("Save"); MenuItem mi3 = new MenuItem("Copy"); MenuItem mi4 = new MenuItem("Paste"); m1.add(mi1); m1.add(mi2); m2.add(mi3); m2.add(mi4); mb.add(m1); mb.add(m2); setMenuBar(mb); winadapt w = new winadapt(this); addWindowListener(w); mnuhandler handler = new mnuhandler(this); mi1.addActionListener(handler); mi2.addActionListener(handler); mi3.addActionListener(handler); } public void paint(Graphics g) { g.drawString(msg,100,100); } } class mnuhandler implements ActionListener { fram f1; public mnuhandler(fram f2) { f1 = f2; } public void actionPerformed(ActionEvent ae) { String msg; String s = (String) ae.getActionCommand(); if(s.equals("Open")) msg = "Open"; else if(s.equals("Save")) msg ="Save"; else if(s.equals("Copy")) msg = "Copy"; else msg = "Paste"; msg = msg +" selected"; f1.msg=msg; f1.repaint(); } }
class winadapt extends WindowAdapter { fram f1; public winadapt(fram f2) { f1 = f2; } public void windowClosing(WindowEvent e) { f1.dispose(); } } public class frammenu extends Applet { Frame f; public void init() { f = new fram(); f.setSize(300,300); f.setVisible(true); } }
10. Wrapper Classes - java.lang double doubleValue( ) float floatValue( ) long longValue( ) int intValue( ) String toString( ) Boolean boleanValue( ) char charValue( ) Double and Float boolean isNaN( ) boolean isInfinite( ) boolean equals(object obj) int hashCode( ) Integer static int parseInt(String str) throws NumberFormatException static String toHexString(int num) static String toOctalString(int num) static Integer valueOf(String str) throws NumberFormatException Character isDigit( ) isLetter( ) isUpperCase( ) isLowerCase( ) toLowerCase( ) toUpperCase( ) toTitleCase( ) Process void destroy( ) int exitValue( ) InputStream getErrorStream( ) InputStream getInputStream( ) OutputStream getOutputStream( )
Runtime process exec(String progName) throws IOException long freeMemory( ) void gc( ) static Runtime getRuntime( ) long totalMemory( ) void runFinalization( ) System static void arraycopy(Object source, int sstart, object target, int tstart, int size); static void gc( ) static void load(String librayfileName) void runFinalization( ) static long currentTimeMillis( ) Object Object clone( ) throws CloneNotsupportedException boolean equals(Object obj) void finalize( ) throws Throwable int hashCode( ) int notify( ) int notifyAll( ) final void wait( ) throws InterruptedException string toString( ) final Class getClass( )
Class static Class forName(String name) throws ClassNotFoundException string getName( ) Class getSuperclass( ) boolean isInterface( ) ClassLoader getClassLoader( ) Math Transcendental sin(d) cos(d) tan(d) Exponential exp(d) log(d ) pow(d1,d2) sqrt(d) Rounding abs(I) ceil(d) floor(d) max(x,y) min(x,y) round(f)
Thread Thread( ) Thread(ThreadGroup grp,Runnable threadob, String Thname) void destroy( ) interrupt( ) stop( ) yield( ) start( ) run( ) resume( ) list( ) static Thread currentThread( ) final boolean isAlive( ) static boolean interrupted( )
ThreadGroup ThreadGroup(String name) ThreadGroup(ThreadGroup ob,String name) final ThreadGroup getParent( )
Java.net package The objectives are Network Datagram Protocol DatagramPacket Socket DatagramSocket Client/Server TCP/IP Internet (IP) Address Socket Domain Name Service ServerSocket InetAddress URL
Network is a set of computers physically connected together. It enables the sharing of computer pheriperals and resources by different computers. The communication between the computers requires certain set of rules called protocols. Some important protocols are TCP/IP, HTTP, FTP, SMTP and NNTP. Port no 21 is for FTP, 23 is for Telnet, 25 is for e-mail and 80 is for HTTP. IP is a low-level routing protocol that breaks data into small packets and sends them to an address across a network. TCP is a higher level protocol that manages string together these packets, sorting and retransmitting them to reliably transmit your data. UDP (user Datagram Protocol) can be used to support fast, connectionless, unreliable transport of packets. Socket is the place used to plug in just like electric sockets, from the socket the communication starts. Client is the machine, which sends some request to another computer. The computer that does the request is called the Server. A proxy server speaks the client side of protocol to another server. A client would connect to a proxy server, which have no restrictions, and the proxy server would in turn communicate for the client. Every computer connected to the network has unique address it contains four numbers between 0 and 255 separated by period. Ex is 80.0.0.50 It is very difficult to remember the IP of the computer. To overcome this problem domain name service (DNS) is used. It maps the IP address by string of characters. Ex is www.microsoft.com InetAddress is a class, which is used to encapsulate IP address and DNS. InetAddress getLoaclHost( ) throws unknowHostException InetAddress getByName (String hostName) InetAddress getAllByName (String hostName)
URL Uniform Resource Locater. It contains four parts protocol, separated by : and //, host name of IP address, port number, file path. For ex http://www.starwave.com/index.html Constructors of URL throws MalformedURLException URL (String urlspecifier) URL (String protocolName, String hostName, int port,String path) URL (String protocolName, String hostName, String path) getPort( ), getHost( ),getFile( ) and toExternalForm( ) To access content information of a URL, use url.openConnection( ) method. Datagrams Datagrams are bundles of information passed between machines. It contains two classes DatagramPacket for container of data DatagramSocket for send or receive the DatagramPacket DatagramPacket constructors are DatagramPacket (byte data[ ], int size); DatagramPacket (byte data[ ], int size, ipAddress, int port); Methods of DatagramPacket are InetAddress getAddress( ), int getPort( ) , byte( ) , getData( ) and DatagramSocket.send (DatagramPacket d); DatagramSocket.receive (DatagramPacket p); client.java import java.net.*; class client { public static DatagramSocket ds; public static byte buffer[] = new byte[1024]; public static void main(String arg[]) throws Exception { ds = new DatagramSocket(6); while(true) { String a; DatagramPacket p = new DatagramPacket(buffer,buffer.length); ds.receive(p); a=new String(p.getData(),p.getLength(),1); if (a.equals("q")) { System.out.println("Server response is shut off now"); return; } System.out.println(new String(p.getData(),0,p.getLength())); } } }
server.java import java.net.*; class server { public static DatagramSocket ds; public static byte buffer[] = new byte[1024]; public static void main(String a[]) throws Exception { InetAddress ia = InetAddress.getByName("rad-tm-04"); System.out.println(ia); ds = new DatagramSocket(123); int pos=0; while(true) { int c = System.in.read(); switch(c) { case 'q': System.out.println("Server quits"); return; case '\r': break; case '\n': ds.send(new DatagramPacket(buffer,pos,ia,456)); pos=0; break; default: buffer[pos++] = (byte) c; } } } }
TCP/IP TCP/IP sockets are used to implement reliable, bidirectional, persistent, point to point, stream based connection between hosts on the Internet. It contains two classes. They are Socket and ServerSocket. ServerSocket class is designed to wait for clients to connect and Socket class is used to connect to ServerSocket. ServerSocket (int port) ServerSocket (int port, int maxqu) ServerSocket (int port, int maxqu, InetAddress localAddress) ServerSocket has a method accept( ) that waits for client to initiate communication. Socket (String hostName, int port) Socket (InetAddress ipAddress, int port)
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JDBC is a set of Java API for executing SQL statements. Two-Tier Model
Client Machine
DBMS propictary protocol Database server
Three-Tier Model
Client Machine(GUI) HTTP, RMI, CORBA Server Machine
DBMS-proprictary protocol Database Server
Two-Tier Model
In Two-Tier Model, a Java applet or application talks directly to the database. This requires a JDBC driver that can communicate with the particular database management systems accessed. Users SQL statement is delivered to the database and the results of those statements are sent to the user. This is referred to as client/server configuration. Three-Tier Model In this a middle tier is introduced for fast performance. It sends
the SQL statements to the databases. The results of the query are send
to middle tier, which sends them to user.
a) Create a data base students in Ms-Access with table student containing the following fields studid number, sname text, course text and marks number.
class dbappn { static connection con; public static void main(String a[ ]) throws Exception { class.forName("sun.jdbc.odbc.JdbcOdbcdriver"); open( ); select( ); insert( ); delete( ); update( ); select( ); close( ); { /*con = DriverManger.getConnection("dsn","username","pwd"); */ con = DriverManager.getConnection("jdbc:odbc:student","palani","kumar"); con.setAutoCommit(false); } static void close( ) throws SQLException { con.commit( ); con.close( ); } static void select( ) throws SQLException { Statement stmt = con.createStatement( ); ResultSet rs = stmt.executeQuery("Select * from student"); Boolean more = rs.next( ); If (!more) { System.out.println("No rows found"); Return ; } while(more) { System.out.println("ID " : " + rs.getString("studid")); System.out.println("Name : " + rs.getString("sname")); System.out.println("Course : " + rs.getstring("course")); System.out.println("Marks : " + rs.getString("marks")); more = rs.next( ); } rs.close( ); stmt.close( ); } static void insert( ) { try{ Statement stmt = con.createStatement( ); values(100, ‘Subash’,’Java’,80)"); stmt.close( ); System.out.println(rows + " row added"); } catch(SQLException s) { System.out.println("Error"); } } static void delete( ) { try{ Statement stmt = con.createStatement( ); where id = 100; stmt.close( ); System.out.println(rows + " row deleted"); } catch(SQLException s) { System.out.println("Error"); } } static void update( ) { try{ Statement stmt = con.createStatement( ); set marks = 90 where id =100 ; stmt.close( ); System.out.println(rows + " row added"); } catch(SQLException s) { System.out.println("Error"); } } } 13. Remote Method Invocation (RMI) RMI allows java object that executes on one machine to invoke a method that executes on another machine. This is the one method of creating distributed application. Steps to create client/server application using RMI
import java.rmi.*; public interface inter extends Remote { public void getdata(int m,int n) throws RemoteException; int adddata() throws RemoteException; }
client.java import java.rmi.*; public class client { public static void main(String arg[]) { try { int a = Integer.parseInt(arg[1]); int b = Integer.parseInt(arg[2]); int result; inter i = (inter) Naming.lookup("rmi://" + arg[0] + "/Addserver"); System.out.println("client"); i.getdata(a,b); result = i.adddata(); System.out.println(result); }catch(Exception e) { System.out.println("error " + e); } } }
server.java vbnm,import java.rmi.*; import java.rmi.server.*; public class server extends UnicastRemoteObject implements inter { int x,y; public server() throws RemoteException { } public int adddata() throws RemoteException { return x+y; } public void getdata(int m, int n) throws RemoteException { x=m; y=n; } public static void main(String arg[]) { try { server s = new server(); Naming.rebind("Addserver",s); } catch(Exception e) { System.out.println("Exception e"); } } }
Swing is a set of classes that provides more powerful and flexible components than are possible with the AWT. In addition to buttons, check boxes and labels, Swing supplies severals components including tabbed panes, scroll panes, trees, picture buttons, combo box , etc. Unlike AWT components, Swing components are platform independent
since they are written in Java. They are called as lightweight components.
Swing related classes are contained in javax.swing and its subpackages.
JApplet Applets that use Swing must be subclasses of JApplet, which extends Applet. JApplet is rich in functionality than Applets and provides various panes such as content pane, glass pane and root pane. To add a component, obtain the pane then call add( ) method for the pane of the JApplet. Container getContentPane( ) to obtain the content pane void add(comp) to add a component in content pane
Icons Method Int getIconHeight( ) int getIconWidth( ) void paintIcon(comp, Graphics, x, y) void setPressedIcon(icon) void setSelectedIcon(icon) void setRolloverIcon(icon)
JScrollPane(comp, vsb, hsb) The vsb, hsb constants are ScrollPaneConstants.HORIZONTAL_SCROLLBAR_ALWAYS ScrollPaneConstants.HORIZONTAL_SCROLLBAR_AS_NEEDED ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS ScrollPaneConstants.VERTICAL_SCROLLBAR_AS_NEEDED
Example : import javax.swsing.*; import java.awt.*; public class Jlabel extends JApplet { public void init( ) { Container cp = getContentPane( ); ImageIcon ii = new ImageIcon("Birds"); JLabel jl = new JLabel("Birds",ii,JLabel.Center); Cp.add(jl); } }
Example : import javax.swing.*; import java.awt.*; public class jscroll extends JApplet { public void init( ) { Container CP = getContentPane( ); Jpanel jp = new Jpanel( ); jp.setLayout(new GridLayout(20,20)); int b = 0; for(int ii = 0; I<20; I++) { for(k=0;k<20;k++) { jp.add(new JButton("Button " + b)); b++; } }
int h=ScrollPaneConstants.HORIZONTAL_SCROLLBAR_AS_NEEDED; CP.add(jsp, BorderLayout.CENTER); } }
Example : Servlets are small programs that execute on the server side of a Web connection, used to extend the functionality of a Web Server. JSDK Java Servlet Development Kit (JSDK) contains class libraries to create servlets. It contains the utility servletrunner to test the servlets. The basic life cycles of servlets are init( ), service( ) and destroy( ). The steps to create a servlets are
The first two methods throws SerlvelException
The javax.servlet.http Package
Example : Step 1 : colorGet.html <html> <body> <center> <form name ="form1" method ="get" <Select name="color" size="1"> <option value = "Red"> Red </option> <option value="Blue"> Blue </option> </select> <br> <br> <input type = submit value="submit"> </form> </body> </html> Step 2 : colorGetSelvlet.java
import java.io.* ; import javax.servlet.*; import javax.servlet.http.*; public class colorGetServlet extends HttpServlet { public void doGet (HttpServlet request, HttpServletResponse response) throws ServletException, IOException { String color = request.getParameter("color"); response.setContentType("text/html"); PrintWriter pw = response.getWriter( ); pw.println("<B> The selected color is : " ); pw.println(color); pw.close( ); } } Step 3: compile the above program colorGetServlet.java Step 4 : start servlet runner by c:\javawebbrowser2.0\jserv Step 5: Display the web page in the browser. Select
a color and submit.
17. KEYWORDS IN JAVA
/* class , method, constuctor, subclass , superclass, this, super, final, finalize(), garbage collection, method overriding, package, interface, import, extend, implement, private, public, protected, static , try, catch, finally, throw, throws , thread, multhread, run, suspend, resume, start, stop, synchronization, deadlock, applet. */ Bytecode Java compiler generates machine independent bytecode instead of machine dependent exe file. So it gives ‘write once run anywhere’ . Due to this, most of the communication programs are done in Java instead of using C++ or VC++. Class The most important feature of the oop is classes. A class defines the shape and behaviour of an object and is a template for multiple object with similar features. Class contains the decl of instance variables and methods. Constructor A constructor initializes an object immediately upon creation. Once defined, it is automatically called immediately after the object is created before the new operator is completed. It has the same name as class and is similar to method but does not have the return type. Garbage collection When no references to an object exist, that object is assumed to be no longer needed, and the memory occupied by the object is reclaimed. This technique is called garbage collection. finalize( ) This method is called just prior to garbage collection. It means it is called, when an object goes out of scope. new The new operator dynamically allocates memory for
the object and returns reference to it.
this this can be used inside any method to refere to the
current object.
Method overloading It is possible to have two or more methods with same name but different parameters within the same class. This is called method overloading. Method Overriding Whenever there are methods of the same name both in the base class as well as in the derived class and if that method is called by main, the method in the derived class is always executed. This is called overriding. Recursion It is a process of defining something in terms of itself. static When a member is declared as static, it can be accessed before any objects of its class are created and without reference to any object. final variable used to declare constant variable . final float PI=3.14 Inheritance Inheritance is the method of creating new class based on the already existing class. The new class derived is called as sub class or derived class which has all features of the existing class and its own. The existing class is called as super class or base class. Adv : resuablity of code, accessibility of variables and methods of the base class by the derived class. If the class is derived from more than one class
, then it is called as multiple inheritance. This is not available in Java.
extend extend keyword is used to create a subclass from a basic class. super super has two forms. First it calls the superclass’s constructor. The second is used to access a member of the superclass that has been hidden by a member of a subclass. Thread A thread is a line of execution. Using multithreading, we can run the different parts of the program at a time. Synchoronized. This keyword is used with a method to enable synchronization.
It contains an object which allows only one thread to
Network A set of computers and peripherals physically connected together to enable sharing of resources and communication. Java network can be done either by Datagram which contains DatagramPacket for container of data and DatagramSocket which contains send and receive methods or TCP/IP which contains Socket class for client and Serversocket for server. RMI It allows an object running in a system to access a method that runs on another system. It is used to create distributed application in Java. In this rmic compiler is used to create Stub class and Skeleton classes for client and server respectively. Rmiregistry is used to map the name of server. Beans Beans are software component that are reusable in variety of environments. After creating beans, it can be added to toolbar of microsoft office, browser, etc. Servlets Servlets are small program that are executed on the
web server to extend the functionality of the server. It contains two packages
javax.servlet and javax.servlet.http
New in Java 2.0 Swing – contains tabbed panes, scroll panes, picture button, etc. Collections More security mechanisms JIT – to create exe file instead of bytecode Can play wav,au,midi and sudio files Drag and drop capabilities wait( ) , sleep( ) and suspend( ) are deprecated in Java 2.0 Java Plug-in directos browser to use JRE rather than
JVM
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