SAZ4A/SAE4A/BPC41 PROGRAMMING IN JAVA Unit : I - V

Transcription

1 SAZ4A/SAE4A/BPC41 PROGRAMMING IN JAVA Unit : I - V

2 UNIT I -- Introduction to Java -- Features of Java -- Basic Concepts of Object Oriented Programming -- Java Tokens -- Java Statements -- Constants -- Variables -- Data Types -- Type Casting -- Operators -- Expressions -- Control Statements: Branching and Looping Statements. 2

3 Introduction to JAVA Programming James Gosling and Sun Microsystems Oak Java, May 20, 1995, Sun World HotJava : The first Java-enabled Web browser JDK Evolutions : J2SE, J2ME, and J2EE 3

4 Features of JAVA Programming TM 4

5 Object Oriented Programming TM An object Oriented Programming consists of many well-encapsulated objects and the objects interact with each other by sending messages. 5

6 Object Oriented Programming TM Concepts An object contains both data and methods that manipulate that data An object is active, not passive; it does things An object is responsible for its own data, But: it can expose that data to other objects. 6

7 JAVA Tokens Tokens are the various Java program elements which are identified by the compiler. A token is the smallest element of a program that is meaningful to the compiler. 7

8 JAVA Constants -- A constant is a value that never changes during the life of a program-- -- In Java, we use the keyword final in front of a declaration to change it from a variable into a constant. Example: final double PI = 3.14; final double PST = 0.08; 8

9 Variables in JAVA TM A variable provides us with named storage that our programs can manipulate. Each variable in Java has a specific type, which determines the size and layout of the variable's memory. 9

10 Data Types in JAVA TM The data type of a value (or variable) is an attribute that tells what kind of data that value can have. 10

11 Type Conversion in JAVA TM When we assign a value of one data type to the variable of different data type, type conversion must be done in order to match the destination data type. syntax: variable1=(variable1 data type)variable2; 11

12 Operators in JAVA TM Operators are special symbols that perform specific operations on one, two, or three operands, and then return a result. 12

13 JAVA Translation Java source code Java bytecode Java compiler Bytecode interpreter Bytecode compiler The Java compiler (javac) converts the source code into bytecode. Bytecode is a kind of average machine language. This Machine bytecode file (.class file) can be run on any operating system by code using thejava interpreter (java) for that platform. The interpreter is referred to as a Virtual Machine. Thus, Java is an example of a Virtual Machine programming Language. 13

14 Basic Program Development TM 14

15 Sample JAVA Program public class sample { // // Prints a presidential quote. // public static void main (String[] args) { System.out.println ("A quote by Abraham Lincoln:"); } } System.out.println ("Whatever you are, be a good one."); 15

16 Control Statements in JAVA TM Control statements enable us to specify the flow of program control; ie, the order in which the instructions in a program must be executed. They make it possible to make decisions, to perform tasks repeatedly or to jump from one section of code to another. Video Link: 16

17 UNIT II -- Classes, Objects and Methods -- Constructors -- Methods Overloading -- Inheritance -- Overriding Methods -- Finalizer and Abstract Methods -- Visibility Control -- Arrays, Strings and Vectors -- StringBuffer Class -- Wrapper Classes 17

18 Classes, Objects and Methods An object is defined by a class. A class is the blueprint of an object. The class uses methods to define the behaviors of the object. The class that contains the main method of a Java program represents the entire program. A class represents a concept, and an object represents the embodiment of that concept. Multiple objects can be created from the same class. 18

19 Constructors in JAVA Constructor is a special method that gets invoked automatically at the time of object creation. Constructor is normally used for initializing objects with default values unless different values are supplied. Constructor has the same name as the class name. Constructor cannot return values. A class can have more than one constructor as long as they have different signature (i.e., different input arguments syntax). 19

20 Method Overloading Same name, different arguments. Code deals with different argument types rather than forcing the caller to do conversions prior to invoking your method. It can have a different return type. Argument list must be different. Access modifier can be different. A method can be overloaded in the same class or in a subclass. 20

21 INHERITANCE JAVA INHERITANCE 21

22 Overriding Methods The child class provides alternative implementation for parent class method. The key benefit of overriding is the ability to define behavior that's specific to a particular subclass type. Overridden method: In the superclass. Overriding method: In the subclass. Rules of Method Overriding The overriding method must NOT throw checked exceptions that are new or broader than those declared by the overridden method. A checked exception is an exception that is checked at compile time. The compiler will complain if a checked exception is not handled. Examples of checked exceptions: IOException,FileNotFoundException, EOFException 22

23 Overloaded and Overridden Methods 23

24 Visibility Control in JAVA 24

25 Arrays An array is a group of like-typed variables that are referred to by a common name. Arrays in Java work differently than they do in C/C++. In Java all arrays are dynamically allocated. Since arrays are objects in Java, we can find their length using member length.. Video Link : 25

26 String Buffer, String Builder and String Tokenizer String is immutable, if you try to alter their values, another object gets created. StringBuffer and StringBuilder are mutable so they can change their values. 26

27 Constructors of String Buffer Class Constructor of String Buffer Class Description StringBuffer() creates an empty string buffer with the initial capacity of 16. StringBuffer(String str) creates a string buffer with the specified string. StringBuffer(int capacity) creates an empty string buffer with the specified capacity as length. 27

28 JAVA Wrapper Classes All the wrapper classes (Integer, Long, Byte, Double, Float, Short) are subclasses of the abstract class Number. The object of the wrapper class contains or wraps its respective primitive data type. Converting primitive data types into object is called boxing, and this is taken care by the compiler. 28

29 Wrapper Classes An object of a wrapper class can be used in any situation where a primitive value will not suffice Primitive values could not be stored in such containers, but wrapper objects could be stored. 29

30 UNIT III -- Interfaces -- Packages -- Creating Packages -- Accessing a Package -- Multithreaded Programming -- Creating Threads -- Stopping and Blocking a Thread -- Life Cycle of a Thread -- Using Thread Methods -- Thread Priority -- Synchronization -- Implementing the Runnable Interface 30

31 Interface An interface is similar to an abstract class with the following exceptions: All methods defined in an interface are abstract. Interfaces can contain no implementation Interfaces cannot contain instance variables. However, they can contain public static final variables (ie. constant class variables) Interfaces are declared using the "interface" keyword. If an interface is public, it must be contained in a file which has the same name. Interfaces are more abstract than abstract classes Interfaces are implemented by classes using the "implements" keyword. 31

32 Declaring an Interface public interface Steerable { public void turnleft(int degrees); public void turnright(int degrees); } public class Car extends Vehicle implements Steerable { public int turnleft(int degrees) { [...] } public int turnright(int degrees) { [...] } When a class "implements" an interface, the compiler ensures that it provides an implementation for all methods defined within the interface. 32

33 JAVA Packages Package: A Package is a collection of related classes. It can also "contain" sub-packages. Sub-packages can have similar names, but are not actually contained inside. java.awt does not contain java.awt.event Uses of Java packages: Group related classes together. As a namespace to avoid name collisions. Provide a layer of access / protection. Keep pieces of a project down to a manageable size. 33

34 The Directory Structure of Packages Two major results occur when a class is placed in a package The name of the package becomes a part of the name of the class. The name of the package must match the directory structure where the corresponding bytecode resides. 34

35 Packages and Directories package directory (folder) class file A class named D in package a.b.c should reside in this file: a/b/c/d.class The "root" directory of the package hierarchy is determined by your class path or the directory from which java was run. Package Declaration package name; public class name {... Example: package sample el; public class e1 extends e2 {... } File e2.java should go in folder sample. Video Link: 35

36 A Multithreaded Programming A multi-threaded program contains two or more parts that can run concurrently and each part can handle a different task at the same time making optimal use of the available resources specially when your computer has multiple CPUs. 36

37 Multithreaded Programming - Thread States A thread can be in one of five states: New, Ready, Running, Blocked, or Finished. Thread created New start() Ready yield(), or time out run() join() Running run() returns 37 Finished Target finished interrupt() sleep() wait() Wait for target to finish Wait for time out Wait to be notified Blocked Time out notify() or notifyall() Interrupted() 37

38 How does a Thread run? The thread class has a run() method run() is executed when the thread's start() method is invoked The thread terminates if the run method terminates To prevent a thread from terminating, the run method must not end run methods often have an endless loop to prevent thread termination One thread starts another by calling its start method The sequence of events can be confusing to those more familiar with a single threaded model. Thread1 start() Thread Object run() Thread2 38

39 The Thread Class 39 «interface» java.lang.runnable java.lang.thread +Thread() +Thread(task: Runnable) +start(): void +isalive(): boolean +setpriority(p: int): void +join(): void +sleep(millis: long): void +yield(): void +interrupt(): void Creates a default thread. Creates a thread for a specified task. Starts the thread that causes the run() method to be invoked by the JVM. Tests whether the thread is currently running. Sets priority p (ranging from 1 to 10) for this thread. Waits for this thread to finish. Puts the runnable object to sleep for a specified time in milliseconds. Causes this thread to temporarily pause and allow other threads to execute. Interrupts this thread. 39

40 Blocking Threads When reading from a stream, if input is not available, the thread will block Thread is suspended ( blocked ) until I/O is available Allows other threads to automatically activate When I/O available, thread wakes back again Becomes runnable Not to be confused with the Runnable interface 40

41 Thread Scheduling In general, the runnable thread with the highest priority is active (running) Java is priority-preemptive If a high-priority thread wakes up, and a low-priority thread is running Then the high-priority thread gets to run immediately Allows on-demand processing -- Efficient use of CPU 41

42 Thread Priorities A Thread inherits the priority of its parent thread. We can increase or decrease the priority of any thread with the setprioritymethod. We can set the priority to any value between MIN_PRIORITY (0) and MAX_PRIORITY (10). NORM_PRIORITY is defined as 5. 42

43 Thread Synchronization When more than one thread try to access a shared resource, resource will be used by only one thread at a time. The process by which this is achieved is called synchronization. The synchronization keyword in Java creates a block of code referred to as critical section. 43

44 Thread Synchronization class Table{ void printtable(int n){//method not synchronized for(int i=1;i<=5;i++){ System.out.println(n*i); try{ Thread.sleep(400); }catch(exception e){system.out.println(e);} } } } class MyThread1 extends Thread{ Table t; MyThread1(Table t){ this.t=t; } public void run(){ t.printtable(5); } } class MyThread2 extends Thread{ Table t; MyThread2(Table t){ this.t=t; } public void run(){ t.printtable(100); } } class TestSynchronization1{ public static void main(string args[]){ Table obj = new Table();//only one object MyThread1 t1=new MyThread1(obj); MyThread2 t2=new MyThread2(obj); t1.start(); t2.start(); } } 44

45 Implementing the Runnable Interface By implementing Runnable interface, we need to provide implementation for run() method. To run this implementation class, create a Thread object, pass Runnable implementation class object to its constructor. 45

46 UNIT IV -- Managing Errors and Exceptions -- Syntax of Exception Handling Code -- Using Finally Statement -- Throwing Our Own Exceptions -- Applet Programming, Applet Life Cycle -- Graphics Programming -- Managing Input/Output Files -- Stream Classes -- Byte Stream Classes -- Character Stream Classes -- Using the File Class, Random Access Files -- Other Stream Classes 46

47 Exceptions and Errors When a problem encounters and unexpected termination or fault, it is called an exception When we try and divide by 0 we terminate abnormally. Exception handling gives us another opportunity to recover from the abnormality. Situations from which we cannot recover like Out of memory are considered as errors. 47

48 JAVA Exception Hierarchy 48

49 Exception Handling /** Set a new radius */ public void setradius(double newradius) throws IllegalArgumentException { if (newradius >= 0) radius = newradius; else throw new IllegalArgumentException("Radius cannot be negative"); } try { statements; // Statements that may throw exceptions } catch (Exception1 exvar1) { handler for exception1; } catch (Exception2 exvar2) { handler for exception2; }... catch (ExceptionN exvar3) { handler for exceptionn; } 49

50 JAVA Applets Java applications Run in stand-alone mode No additional software required Java applets Compiled Java class files Run within a Web browser (or an appletviewer) Loaded from anywhere on the Internet security restrictions 50

51 Applet Life Cycle When an applet begins the following sequence of methods is called init() informs applet that it has been loaded into the system Called only once an ideal place to initialize variables and create UI objects start() informs applet that it should start its execution Right after init() Each time the page is loaded and restarted When an applet dies (or is terminated), the following sequence of method calls takes place: stop() informs applet that it should stop its execution When a web browser leaves the HTML document 51

52 JAVA Coordinate System Component Hierarchy Each component has its own subwindow Subwindow = rectangular area within parent component Has own coordinate system Clipping: Can t paint outside its subwindow Can t paint over child components. 52

53 Graphics Primitives Point (x,y) Line (pt1,pt2) PolyLine (pt list) Arc Oval (pt, w,h) Rectangle (pt, w,h) RoundRectangle Polygon (pt list) Image (file, x,y) Text (string, x,y) Draw label Fill 53

54 Graphics Methods drawstring(string, left, bottom) Draws a string in the current font and color with the bottom left corner of the string at the specified location One of the few methods where the y coordinate refers to the bottom of shape, not the top. But y values are still with respect to the top left corner of the applet window drawrect(left, top, width, height) Draws the outline of a rectangle (1-pixel border) in the current color fillrect(left, top, width, height) Draws a solid rectangle in the current color drawline(x1, y1, x2, y2) Draws a 1-pixel-thick line from (x1, y1) to (x2, y2) 54

55 Graphics Methods drawoval, filloval Draws an outlined and solid oval, where the arguments describe a rectangle that bounds the oval. drawpolygon, fillpolygon Draws an outlined and solid polygon whose points are defined by arrays or a Polygon (a class that stores a series of points) By default, polygon is closed; to make an open polygon use the drawpolyline method. drawimage Draws an image Images can be in JPEG or GIF (including GIF89A) format Video Link: 55

56 Concept of Streams A stream can be defined as a sequence of data. InputStream: The InputStream is used to read data from a source. OutPutStream: the OutputStream is used for writing data to a destination. 56

57 JAVA Stream Classes Stream classes is java is used for reading and writing data. The Java Stream Classes are the part of java.io. 57

58 Character Stream and Byte Stream Classes in JAVA 58

59 Random Access Files Random access files are files in which records can be accessed in any order Also called direct access files More efficient than sequential access files 59

60 Input Output Streams in JAVA The InputStream is used to read data from a source file. The OutputStream is used for writing data to a destination file. 60

61 UNIT V -- Network basics -- Socket programming -- Proxy servers -- TCP/IP -- Net Address -- URL, Datagrams -- Java Utility Classes -- Introducing the AWT -- Working with Windows, Graphics and Text- AWT Classes -- Working with Frames, Working with Graphics, -- Working with Color, Working with Fonts -- Using AWT Controls, Layout Managers and Menus 61

62 Network Programming Mechanisms by which software running on two or more computational devices can exchange messages. Java is a network centric programming language. Java abstracts details of network implementation behind a standard API. Applications Application Protocols Streams Unicast Broadcast Datagrams Multicast Addressing & Routing Physical Transport 62

63 Socket Programming with TCP The application developer has the ability to fix a few TCP parameters, such as maximum buffer and maximum segment sizes. Video Link: 63

64 JAVA Socket Programming Sockets provide the communication between two computers using TCP. A client program creates a socket on its end of the communication and attempts to connect that socket to a server. When the connection is made, the server creates a socket object on its end of the communication. 64

65 Mechanism of Proxy Server A proxy is a host which relays web access requests from clients. Used when clients do not access the web directly Used for security, logging, accounting and performance 65

66 JAVA Utility Classes Java.util package contains the collections framework, legacy collection classes, event model, date and time facilities, internationalization, and miscellaneous utility classes. 66

67 JAVA AWT Component Java AWT (Abstract Window Toolkit) is an API to develop GUI or windowbased applications in java. Java AWT components are platform-dependent. AWT is heavyweight components. 67

68 Working with Frames A frame, implemented as an instance of the JFrame class, is a window that has decorations such as a border, a title, and supports button components that close or iconify the window. 68

69 Working with Colors in JAVA The Color class states colors in default RGB color space. Class declaration for java.awt.color class: public class Color extends Object implements Paint, Serializable 69

70 JAVA Fonts 70

71 JAVA LayoutManager Layout manager automatically positions the components within container. The layout manager is associated with every Container object. Each layout manager is an object of the class that implements the Layout Manager interface. 71

72 Java LayoutManagers LayoutManager is an interface that is implemented by all the classes of layout managers. There are following classes that represents the layout managers: java.awt.borderlayout java.awt.flowlayout java.awt.gridlayout java.awt.cardlayout java.awt.gridbaglayout javax.swing.boxlayout javax.swing.grouplayout javax.swing.scrollpanelayout javax.swing.springlayout 72

73 Example of BorderLayout class: import java.awt.*; import javax.swing.*; public class Border { JFrame f; Border(){ f=new JFrame(); JButton b1=new JButton("NORTH");; JButton b2=new JButton("SOUTH");; JButton b3=new JButton("EAST");; JButton b4=new JButton("WEST");; JButton b5=new JButton("CENTER");; f.add(b1,borderlayout.north); f.add(b2,borderlayout.south); f.add(b3,borderlayout.east); f.add(b4,borderlayout.west); f.add(b5,borderlayout.center); f.setsize(300,300); f.setvisible(true); } public static void main(string[] args) { new Border(); } } Output: 73

74 Java JMenuBar, JMenu and JMenuItem The JMenuBar class is used to display menubar on the window or frame Menu and MenuItem controls are subclass of MenuComponent class. JMenuBar class declaration public class JMenuBar extends JComponent implements MenuElement, Accessible JMenu class declaration public class JMenu extends JMenuItem implements MenuElement, Accessible JMenuItem class declaration public class JMenuItem extends AbstractButton implements Accessible, MenuElement SAZ4A Programming in JAVA 74

75 import javax.swing.*; class MenuExample { JMenu menu, submenu; JMenuItem i1, i2, i3, i4, i5; MenuExample(){ JFrame f= new JFrame("Menu and MenuItem Example"); JMenuBar mb=new JMenuBar(); menu=new JMenu("Menu"); submenu=new JMenu("Sub Menu"); i1=new JMenuItem("Item 1"); i2=new JMenuItem("Item 2"); i3=new JMenuItem("Item 3"); i4=new JMenuItem("Item 4"); i5=new JMenuItem("Item 5"); menu.add(i1); menu.add(i2); menu.add(i3); submenu.add(i4); submenu.add(i5); menu.add(submenu); mb.add(menu); f.setjmenubar(mb); f.setsize(400,400); f.setlayout(null); f.setvisible(true); } public static void main(string args[]) { new MenuExample(); }} Output: SAZ4A Programming in JAVA 1 / 75