Java lab lecture 1
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The document discusses the need for a platform-independent language for developing applications that can run on heterogeneous systems. It describes how James Gosling and his team at Sun Microsystems created the Java programming language to address this need. The key aspects that allow Java to achieve platform independence are: 1) Java source code is compiled to bytecode that runs on the Java Virtual Machine (JVM) instead of native machine code, 2) The JVM specification ensures bytecode can be run on any system with a compatible JVM implementation.
![Class MyExample
{
public Static Void main(String arr[])
{
System.out.println(“this is my example”);
}
}](https://image.slidesharecdn.com/javalablecture-1-220203074551/85/Java-lab-lecture-1-38-320.jpg)
![Class Rectangle
{
int l,b
//attribute
public void display()
{
System.out.println(“Length=”+l);
System.out.println(“Breadth=”+b);
}
public int area()
{
Return l*b;
}
Public void setDimension(int x,int y)
{
I=x;
B=y;
}
}
Class RectangleTest
{
public static void main(String
arr[])
{
Rectangle r = new Rectangle();
r.setDimension(20,30)
{
System.out.println(“dimension of
rectangle are”);
r.display();
System.out.println(“area of
rectangle r is =”+r.area());
}}](https://image.slidesharecdn.com/javalablecture-1-220203074551/85/Java-lab-lecture-1-44-320.jpg)
Java lab lecture 1
- 2. With the invention of internet and world wide web there is need of a language that should be platform independent. On internet we don't know in advance at what platform our code or program /application will be executed as all over the world there are heterogeneous systems.
- 3. JAVA was not made for Internet programming. Java was developed for Microcontroller for platform neutral execution. so there is no need to rewrite the code each time for every Microcontroller.
- 4. James Gosling and his team start working on a portable ,platform independent language that could be used to produce code that would run on variety of CPU under different environment. This effort leads to creation of JAVA
- 5. In portable language we can compile the code by using different compiler on different operating system. e.g. in C source code On DOS we can compile the source code by Turbo Borland Compiler On Window we can compile using VC++ Compiler For UNIX we can use CC/GCC compiler
- 6. JAVA VIRTUAL MACHINE is the solution for platform independent compilation
- 7. Specification designed by SUN Microsystems 1. Instruction set 2. File format 3. Class loading and execution Mechanism etc. JVM is specification of JRE JRE is implementation of JVM JRE can be called JVM but JVM cannot be called JRE. Car is called a Vehicle but Vehicle is not called Car
- 8. A software vendor who wants to develop JRE needs JVM Main component of JRE 1 Byte code verifier 2.Class Loader 3.Just in time Compiler 4.Class Library 5.Security Policies 6.Memory Management.
- 9. It is the package of JRE and tools(javac ,javap ,jar etc.) (jar is compression and decompression format of sun micro system) 1. Application programmer needs JDK 2. End user needs JRE 3. A software vendor who wants to develop JRE needs JVM(specification and license from SunMicrosystem now owned by Oracle). 4. Every vendor can develop their own compiler of java with license from sun micro system according to their need.
- 10. The key to solve the security and portability problem is that the output of Java compiler is not executable code rather than it is BYTECODE. Byte Code is a highly optimized set of instructions to be executed by JRE(some time called JVM) JVM was designed as an interpreter for byte code. JVM may be different from platform to platform but all understand the same byte code.
- 11. In real world we think in the form of object. We give preference to object than on work that object perform. e.g: Teacher, Carpenter JAVA designer want to develop a language that should solve the problems that have solution similar real world problems. If we want to study we looks for teacher. If we want to make a table, chair or any furniture we looks for carpenter
- 12. Object is an Instance of class At particular moment how that class is behaving is know as object Suppose Light is class Either it is on ,off,dim,bright Light is on Light is off Light is bright Light is Dim
- 15. it is the way of thinking in terms of object on the basis of this thinking a programming model created by sun micro system in known as object oriented programming structure SUN MicroSystem is a microelectronics company designing chips for microcontroller used in washing machines ,digital set top box,Remote control etc. What is difference between microcontroller and microprocessor?
- 16. Java's main features are 1. Platform independent. 2. Security
- 17. For each platform we have to write a new code. If a company is making 100 microcontroller per day then 100 times we have to write the code. because language depends on the properties of hardware(instruction set, instruction format, type of register)
- 18. Main Feature of Java: 1. Simple 2. Secure(The JVM performs verification on bytecode before running it to prevent the program from performing unsafe operations such as branching to incorrect locations) 3. Object-Oriented 4. Robust(Java is robust because it is highly supported language, meaning that unlike C you cannot crash your computer with a bad program) 5. Multithreaded 6. Architectural Neutral (binary code format" that's independent of hardware architectures, operating system interfaces, and window systems) 7. Interpreted. 8. High-performance (Just in time compilation) 9. Distributed (development of application to run over network always need distributed languages) 10. Dynamic (During the execution of a program, Java can dynamically load class libraries )
- 19. It is slow in comparison of C/C++.because it is both compiled and interpreted language. Applet cannot access local data. Only download the data from site where applet is located. No use of pointer so we cannot do flexible data structure design. Need different JVM for different platform. It is strictly types language (every variable have type, every expression has type) so there is no flexibility in programming.
- 20. JAVA C++ 1 Java is completely object oriented language C++ is extension of C with object oriented behavior 2 Java does not support multiple inheritances. But it can be achieved using interface if needed. C++ support multiple inheritance 3 Java does not support global variable Global variable can be declared in C++ 4 Java does not support pointer. C++ support pointers. 5 In Java there is no destructor. In C++ there is use of destructor 6 Java does not provide header file C++ has header file. 7 Java code run on Virtual machine (JVM) C++ code runs on actual machine 8 In java automatic memory management and garbage collection Memory management is done manually by new/delete. 9 Write once run any where Write once compile anywhere
- 27. 1 Single Inheritance 2 Multiple Inheritance 3 Multilevel Inheritance 4 Hierarchical Inheritance 5 Hybrid Inheritance
- 28. single inheritance is simply one subclass extending one superclass. It is the simplest of all.
- 29. Multiple Inheritance is one class extending multiple classes. As discussed before, Java does not support multiple Inheritance. However, with the help of interfaces, we can visualize multiple Inheritance at work.
- 30. A multilevel inheritance is about a superclass extending its features to a subclass, which in turns act as another superclass to a new subclass. Multilevel inheritance is implemented in a hierarchy. This means, once a subclass, will be a future superclass.
- 31. In hierarchical inheritance, one class acts as a parent class for multiple subclasses.
- 32. Hybrid inheritance is formed as a result of the combination of both single and multiple Inheritance. As multiple Inheritance is not viable with classes, we achieve hybrid inheritance through interfaces.
- 38. Class MyExample { public Static Void main(String arr[]) { System.out.println(“this is my example”); } }
- 39. The word Class means that a new class is defined. MyExample is an identifier(called class name) All members of class should be declared inside curly braces {…………….} Execution always start from main method. The keyword public mean that member may be accessed by code outside the class in which it is declared. main() must be declared as public since it must be called by the code outside of its class when the program is started. Keyword static allow main() to be called without having to instantiate a particular instance of class. since main() is called by JVM before any object are made.
- 40. Keyword void tells the compiler that main() does not return a value. Object of type String store character string in this case arr is an command line argument presents when program is executed. System is a predefined class that provides access to the system and out is output stream that is connected to console.
- 41. Execution Model of C and C++ 1.Application file is read and format is checked. 2.If format is valid .its instruction is loaded. 3.Address of first Inst. Is loaded in PC 4.Process asked to start execution. 5.Address of Instruction fetched from PC one by one. 6.Instruction is fetched from memory and is executed.
- 42. 2.Class file is read and its format is checked. 3,4.If format is valid, class loader is asked to load it. 5.Just in time compiler(JITC) is asked to execute the class. 6.Instruction of class is read one by one. 7.For each instruction security policy is checked and instruction is executed only if it satisfy security policy.
- 43. . Eclipse
- 44. Class Rectangle { int l,b //attribute public void display() { System.out.println(“Length=”+l); System.out.println(“Breadth=”+b); } public int area() { Return l*b; } Public void setDimension(int x,int y) { I=x; B=y; } } Class RectangleTest { public static void main(String arr[]) { Rectangle r = new Rectangle(); r.setDimension(20,30) { System.out.println(“dimension of rectangle are”); r.display(); System.out.println(“area of rectangle r is =”+r.area()); }}
- 45. Classname refrencevariable = new classname(); Reference variable is a implicit pointer which is used to contain the reference of objects. In java reference variable are dynamically created. Hence they don’t have name and are referenced through their reference variables. In C++: there is static allocation of objects r Rectangle r ======== r l b