History of Java. VM (Java Virtual Machine) What is JVM. What it does. 1. Brief history of Java 2. Java Version History

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1 Histry f Java 1. Brief histry f Java 2. Java Versin Histry The histry f Java is very interesting. Java was riginally designed fr interactive televisin, but it was t advanced technlgy fr the digital cable televisin industry at the time. The histry f java starts frm Green Team. Java team members (als knwn as Green Team), initiated this prject t develp a language fr digital devices such as set-tp bxes, televisins etc. But, it was suited fr internet prgramming. Later, Java technlgy was incrprated by Netscape. Currently, Java is used in internet prgramming, mbile devices, games, e-business slutins etc. There are given the majr pints that describe the histry f java. VM (Java Virtual Machine) 1. Java Virtual Machine 2. Internal Architecture f JVM JVM (Java Virtual Machine) is an abstract machine. It is a specificatin that prvides runtime envirnment in which java bytecde can be executed. JVMs are available fr many hardware and sftware platfrms (i.e. JVM is platfrm dependent). What is JVM It is: 1. A specificatin where wrking f Java Virtual Machine is specified. But implementatin prvider is independent t chse the algrithm. Its implementatin has been prvided by Sun and ther cmpanies. 2. An implementatin Its implementatin is knwn as JRE (Java Runtime Envirnment). 3. Runtime Instance Whenever yu write java cmmand n the cmmand prmpt t run the java class, an instance f JVM is created. What it des The JVM perfrms fllwing peratin: Lads cde Verifies cde Executes cde

2 Prvides runtime envirnment JVM prvides definitins fr the: Memry area Class file frmat Register set Garbage-cllected heap Fatal errr reprting etc. Internal Architecture f JVM Let's understand the internal architecture f JVM. It cntains classlader, memry area, executin engine etc.

3 1) Classlader Class lader is a subsystem f JVM that is used t lad class files. 2) Class(Methd) Area Class (Methd) Area stres per-class structures such as the runtime cnstant pl, field and methd data, the cde fr methds. 3) Heap It is the runtime data area in which bjects are allcated. 4) Stack Java Stack stres frames. It hlds lcal variables and partial results, and plays a part in methd invcatin and return. Each thread has a private JVM stack, created at the same time as thread. A new frame is created each time a methd is invked. A frame is destryed when its methd invcatin cmpletes. 5) Prgram Cunter Register PC (prgram cunter) register cntains the address f the Java virtual machine instructin currently being executed. 6) Native Methd Stack It cntains all the native methds used in the applicatin. 7) Executin Engine It cntains: 1) A virtual prcessr 2) Interpreter: Read bytecde stream then execute the instructins. 3) Just-In-Time (JIT) cmpiler: It is used t imprve the perfrmance. JIT cmpiles parts f the byte cde that have similar functinality at the same time, and hence reduces the amunt f time needed fr cmpilatin. Here the term cmpiler refers t a translatr frm the

4 instructin set f a Java virtual machine (JVM) t the instructin set f a specific CPU. Differences amng C, C++, Java : The main difference between c++ and java is that C++ des nt supprt database cnnectin while Java supprts database cnnectin.the ther differences can be summarized as : Aspects C C++ Java Develped Year Develped By Dennis Ritchie Bjarne Strustrup James Gsling Successr f BCPL C C(Syntax) & C++ (Structure) Paradigms Prcedural Object Oriented Object Oriented Platfrm Dependency Dependent Dependent Independent Keywrds defined (gt, cnst unusable) Datatypes : unin, structure Supprted Supprted Nt Supprted Pre-prcessr directives Supprted (#include, #define) Supprted (#include, #define) Nt Supprted

5 Header files Supprted Supprted Use Packages (imprt) Inheritance N Inheritance Supprted Multiple Inheritance nt Supprted Overlading N Overlading Supprted Operatr Overlading nt Supprted Pinters Supprted Supprted N Pinters Cde Translatin Cmpiled Cmpiled Interpreted Strage Allcatin Uses mallc, callc Uses new, delete uses garbage cllectr Multi-threading and Interfaces Nt Supprted Nt Supprted Supprted Exceptin Handling N Exceptin handling Supprted Supprted Templates Nt Supprted Supprted Nt Supprted Strage class: aut, extern Supprted Supprted Nt Supprted Destructrs N Cnstructr r Destructr Supprted Nt Supprted

6 Database Cnnectivity Nt Supprted Nt Supprted Supprted Data Types in Java Data types represent the different values t be stred in the variable. In java, there are tw types f data types: Primitive data types Nn-primitive data types Data Type Default Value Default size blean false 1 bit

7 char '\u0000' 2 byte byte 0 1 byte shrt 0 2 byte int 0 4 byte lng 0L 8 byte flat 0.0f 4 byte duble 0.0d 8 byte Java If-else Statement The Java if statement is used t test the cnditin. It checks blean cnditin: true r false. There are varius types f if statement in java. if statement if-else statement if-else-if ladder nested if statement Java if Statement The Java if statement tests the cnditin. It executes the if blck if cnditin is true. Syntax: 1. if(cnditin){ 2. //cde t be executed

8 Java Array Nrmally, array is a cllectin f similar type f elements that have cntiguus memry lcatin. Java array is an bject the cntains elements f similar data type. It is a data structure where we stre similar elements. We can stre nly fixed set f elements in a java array. Array in java is index based first element f the array is stred at 0 index. Advantage f Java Array Cde Optimizatin: It makes the cde ptimized, we can retrieve r srt the data easily. Randm access: We can get any data lcated at any index psitin. Disadvantage f Java Array Size Limit: We can stre nly fixed size f elements in the array. It desn't grw its size at runtime. T slve this prblem, cllectin framewrk is used in java. Types f Array in java There are tw types f array.

9 Single Dimensinal Array Multidimensinal Array Object and Class in Java 1. Object in Java 2. Class in Java 3. Instance Variable in Java 4. Methd in Java 5. Example f Object and class that maintains the recrds f student 6. Annymus Object In this page, we will learn abut java bjects and classes. In bject-riented prgramming technique, we design a prgram using bjects and classes. Object is the physical as well as lgical entity whereas class is the lgical entity nly. Object in Java An entity that has state and behavir is knwn as an bject e.g. chair, bike, marker, pen, table, car etc. It can be physical r lgical (tangible and intangible). The example f intangible bject is banking system. An bject has three characteristics:

10 state: represents data (value) f an bject. behavir: represents the behavir (functinality) f an bject such as depsit, withdraw etc. identity: Object identity is typically implemented via a unique ID. The value f the ID is nt visible t the external user. But, it is used internally by the JVM t identify each bject uniquely. Fr Example: Pen is an bject. Its name is Reynlds, clr is white etc. knwn as its state. It is used t write, s writing is its behavir. Object is an instance f a class. Class is a template r blueprint frm which bjects are created. S bject is the instance (result) f a class. Object Definitins: Object is a real wrld entity. Object is a run time entity. Object is an entity which has state and behavir. Object is an instance f a class. Class in Java A class is a grup f bjects which have cmmn prperties. It is a template r blueprint frm which bjects are created. It is a lgical entity. It can't be physical. A class in Java can cntain: fields methds cnstructrs blcks nested class and interface Syntax t declare a class: 1. class <class name>{ 2. field; 3. methd; 4. }

11 Instance variable in Java A variable which is created inside the class but utside the methd, is knwn as instance variable. Instance variable desn't get memry at cmpile time. It gets memry at run time when bject(instance) is created. That is why, it is knwn as instance variable. Methd in Java In java, a methd is like functin i.e. used t expse behavir f an bject. Advantage f Methd Cde Reusability Cde Optimizatin Inheritance in Java 1. Inheritance 2. Types f Inheritance 3. Why multiple inheritance is nt pssible in java in case f class? Inheritance in java is a mechanism in which ne bject acquires all the prperties and behavirs f parent bject. The idea behind inheritance in java is that yu can create new classes that are built upn existing classes. When yu inherit frm an existing class, yu can reuse methds and fields f parent class, and yu can add new methds and fields als. Inheritance represents the IS-A relatinship, als knwn as parent-child relatinship. Why use inheritance in java Fr Methd Overriding (s runtime plymrphism can be achieved). Fr Cde Reusability. Syntax f Java Inheritance 1. class Subclass-name extends Superclass-name 2. { 3. //methds and fields 4. } The extends keywrd indicates that yu are making a new class that derives frm an existing class. The meaning f "extends" is t increase the functinality.

12 In the terminlgy f Java, a class which is inherited is called parent r super class and the new class is called child r subclass. Java Inheritance Example As displayed in the abve figure, Prgrammer is the subclass and Emplyee is the superclass. Relatinship between tw classes is Prgrammer IS-A Emplyee.It means that Prgrammer is a type f Emplyee. 1. class Emplyee{ 2. flat salary=40000; 3. } 4. class Prgrammer extends Emplyee{ 5. int bnus=10000; 6. public static vid main(string args[]){ 7. Prgrammer p=new Prgrammer(); 8. System.ut.println("Prgrammer salary is:"+p.salary); 9. System.ut.println("Bnus f Prgrammer is:"+p.bnus); 10. } 11. } Test it Nw Prgrammer salary is: Bnus f prgrammer is:10000 In the abve example, Prgrammer bject can access the field f wn class as well as f Emplyee class i.e. cde reusability.

13 Types f inheritance in java On the basis f class, there can be three types f inheritance in java: single, multilevel and hierarchical. In java prgramming, multiple and hybrid inheritance is supprted thrugh interface nly. We will learn abut interfaces later. Nte: Multiple inheritance is nt supprted in java thrugh class. When a class extends multiple classes i.e. knwn as multiple inheritance. Fr Example:

14 Interface in Java 1. Interface 2. Example f Interface 3. Multiple inheritance by Interface 4. Why multiple inheritance is supprted in Interface while it is nt supprted in case f class. 5. Marker Interface 6. Nested Interface An interface in java is a blueprint f a class. It has static cnstants and abstract methds. The interface in java is a mechanism t achieve abstractin. There can be nly abstract methds in the java interface nt methd bdy. It is used t achieve abstractin and multiple inheritance in Java. Java Interface als represents IS-A relatinship. It cannt be instantiated just like abstract class. Why use Java interface? There are mainly three reasns t use interface. They are given belw. It is used t achieve abstractin. By interface, we can supprt the functinality f multiple inheritances. It can be used t achieve lse cupling. Java 8 Interface Imprvement Since Java 8, interface can have default and static methds which are discussed later. Internal additin by cmpiler The java cmpiler adds public and abstract keywrds befre the interface methd. Mre, it adds public, static and final keywrds befre data members. In ther wrds, Interface fields are public, static and final by default, and methds are public and abstract.

15 Understanding relatinship between classes and interfaces As shwn in the figure given belw, a class extends anther class, an interface extends anther interface but a class implements an interface. Java Applet Applet is a special type f prgram that is embedded in the webpage t generate the dynamic cntent. It runs inside the brwser and wrks at client side. Advantage f Applet There are many advantages f applet. They are as fllws: It wrks at client side s less respnse time. Secured It can be executed by brwsers running under many platefrms, including Linux, Windws, Mac Os etc. Drawback f Applet Plugin is required at client brwser t execute applet.

16 D Yu Knw Wh is respnsible t manage the life cycle f an applet? Hw t perfrm animatin in applet? Hw t paint like paint brush in applet? Hw t display digital clck in applet? Hw t display analg clck in applet? Hw t cmmunicate tw applets? Hierarchy f Applet As displayed in the abve diagram, Applet class extends Panel. Panel class extends Cntainer which is the subclass f Cmpnent. Lifecycle f Java Applet 1. Applet is initialized. 2. Applet is started. 3. Applet is painted. 4. Applet is stpped. 5. Applet is destryed.

17 Lifecycle methds fr Applet: The java.applet.applet class 4 life cycle methds and java.awt.cmpnent class prvides 1 life cycle methds fr an applet. java.applet.applet class Fr creating any applet java.applet.applet class must be inherited. It prvides 4 life cycle methds f applet. 1. public vid init(): is used t initialized the Applet. It is invked nly nce. 2. public vid start(): is invked after the init() methd r brwser is maximized. It is used t start the Applet. 3. public vid stp(): is used t stp the Applet. It is invked when Applet is stp r brwser is minimized. 4. public vid destry(): is used t destry the Applet. It is invked nly nce. java.awt.cmpnent class The Cmpnent class prvides 1 life cycle methd f applet. 1. Public vid paint (Graphics g): is used t paint the Applet. It prvides Graphics class bject that can be used fr drawing val, rectangle, arc etc. Wh is respnsible t manage the life cycle f an applet? Java Plug-in sftware. Hw t run an Applet? There are tw ways t run an applet 1. By html file. 2. By appletviewer tl (fr testing purpse).