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Note for Java Programming - JAVA By JNTU Heroes

  • Java Programming - JAVA
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  • Jawaharlal Nehru Technological University Anantapur (JNTU) College of Engineering (CEP), Pulivendula, Pulivendula, Andhra Pradesh, India - JNTUACEP
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simple applications- Layout management – Layout manager types – border- grid and flow Event Handling: Events- Event sources- Event classes- Event Listeners- Relationship between Event sources and Listeners- Delegation event model- Example: handling a button clickhandling mouse events- Adapter classes. Applets – Inheritance hierarchy for applets- differences between applets and applications- life cycle of an applet- passing parameters to applets- applet security issues. TEXT BOOK: Java Fundamentals – A comprehensive Introduction- Herbert Schildt and Dale Skrien REFERENCES 1. Java for programmers-P.J.Dietel and H.M.Dietel Pearson education(or)Java: How to program P.J.Dietel and H.M.Dietel-PHI 2. Object Oriented programming through Java -P.Radha Krishna -Universities Press 3. Thinking in Java- Bruce Eckel-Pearson Education 4. Programming in Java- S.Malhotra and S. Choudhary- Oxford University Press. UNIT-1 Topics: OOP concepts- Data abstraction- encapsulation- inheritance- benefits of inheritancepolymorphism-classes and objects- procedural and object oriented programming paradigm. Java programming – History of java- comments data types-variables-constants-scope and life time of variables-operators-operator hierarchy-expressions-type conversion and castingenumerated types- control flow – block scope- conditional statements-loops-break and continue statements- simple java stand alone programs-arrays-console input and output- formatting output-constructors-methods-parameter passing- static fields and methods- access control- this reference- overloading methods and constructors-recursion-garbage collection- building stringsexploring string class. 3

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Introduction Everywhere you look in the real world you see objects—people, animals, plants, cars, planes, buildings, computers and so on. Humans think in terms of objects. Telephones, houses, traffic lights, microwave ovens and water coolers are just a few more objects. Computer programs, such as the Java programs you’ll read in this book and the ones you’ll write, are composed of lots of interacting software objects. We sometimes divide objects into two categories: animate and inanimate. Animate objects are ―alive‖ in some sense—they move around and do things. Inanimate objects, on the other hand, do not move on their own .Objects of both types, however, have some things in common. They all have attributes (e.g., size, shape, color and weight), and they all exhibit behaviors (e.g., a ball rolls, bounces, inflates and deflates; a baby cries, sleep crawls, walks and blinks; a car accelerates, brakes and turns; a towel absorbs water). We will study the kinds of attributes and behaviors that software objects have. Humans learn about existing objects by studying their attributes and observing their behaviors. Different objects can have similar attributes and can exhibit similar behaviors. Comparisons can be made, for example, between babies and adults and between humans and chimpanzees. Object-oriented design provides a natural and intuitive way to view the software design process—namely, modeling objects by their attributes and behaviors just as we describe real-world objects. OOD also models communication between objects. Just as people send messages to one another (e.g., a sergeant commands a soldier to stand at attention), objects also communicate via messages. A bank account object may receive a message to decrease its balance by a certain amount because the customer has withdrawn that amount of money. Object-Oriented: Although influenced by its predecessors, Java was not designed to be source-code compatible with any other language. This allowed the Java team the freedom to design with a blank slate. One outcome of this was a clean, usable, pragmatic approach to objects. Borrowing liberally from many seminal object-software environments of the last few decades, Java manages to strike a balance between the purist’s ―everything is an object‖ paradigm and the pragmatist’s ―stay out of my way‖ model. The object model in Java is simple and easy to extend, while simple types, such as integers, are kept as high-performance nonobjects. OOD encapsulates (i.e., wraps) attributes and operations (behaviors) into objects, an object’s attributes and operations are intimately tied together. Objects have the property of information hiding. This means that objects may know how to communicate with one another across well-defined interfaces, but normally they are not allowed to know how other objects are implemented ,implementation details are hidden within the objects themselves. We can drive a car effectively, for instance, without knowing the details of how engines, transmissions, brakes and exhaust systems work internally—as long as we know how to use the accelerator pedal, the brake pedal, the wheel and so on. Information hiding, as we will see, is crucial to good software engineering. 4

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Languages like Java are object oriented. Programming in such a language is called object-oriented programming (OOP), and it allows computer programmers to implement an object-oriented design as a working system. Languages like C, on the other hand, are procedural, so programming tends to be action oriented. In C, the unit of programming is the function. Groups of actions that perform some common task are formed into functions, and functions are grouped to form programs. In Java, the unit of programming is the class from which objects are eventually instantiated (created). Java classes contain methods (which implement operations and are similar to functions in C) as well as fields (which implement attributes). Java programmers concentrate on creating classes. Each class contains fields, and the set of methods that manipulate the fields and provide services to clients (i.e., other classes that use the class). The programmer uses existing classes as the building blocks for constructing new classes. Classes are to objects as blueprints are to houses. Just as we can build many houses from one blueprint, we can instantiate (create) many objects from one class. Classes can have relationships with other classes. For example, in an object-oriented design of a bank, the ―bank teller‖ class needs to relate to the ―customer‖ class, the ―cash drawer‖ class, the ―safe‖ class, and so on. These relationships are called associations. Packaging software as classes makes it possible for future software systems to reuse the classes. Groups of related classes are often packaged as reusable components. Just as realtors often say that the three most important factors affecting the price of real estate are ―location, location and location,‖ people in the software community often say that the three most important factors affecting the future of software development are ―reuse, reuse and reuse.‖ Reuse of existing classes when building new classes and programs saves time and effort. Reuse also helps programmers build more reliable and effective systems, because existing classes and components often have gone through extensive testing, debugging and performance tuning. Indeed, with object technology, you can build much of the software you will need by combining classes, just as automobile manufacturers combine interchangeable parts. Each new class you create will have the potential to become a valuable software asset that you and other programmers can use to speed and enhance the quality of future software development efforts. NEED FOR OOP PARADIGM: Object-Oriented Programming: Object-oriented programming is at the core of Java. In fact, all Java programs are objectoriented—this isn’t an option the way that it is in C++, for example. OOP is so integral to Java. Therefore, this chapter begins with a discussion of the theoretical aspects of OOP. Two Paradigms of Programming: 5

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As you know, all computer programs consist of two elements: code and data. Furthermore,a program can be conceptually organized around its code or around its data. That is, some programs are written around ―what is happening‖ and others are written around ―who is being affected.‖ These are the two paradigms that govern how a program is constructed. The first way is called the process-oriented model. This approach characterizes a program as a series of linear steps (that is, code). The process-oriented model can be thought of as code acting on data. Procedural languages such as C employ this model to considerable success. Problems with this approach appear as programs grow larger and more complex. To manage increasing complexity, the second approach, called object-oriented programming, was conceived. Object-oriented programming organizes a program around its data (that is, objects) and a set of well-defined interfaces to that data. An object-oriented program can be characterized as data controlling access to code. As you will see, by switching the controlling entity to data, you can achieve several organizational benefits. Procedure oriented Programming: In this approach, the problem is always considered as a sequence of tasks to be done. A number of functions are written to accomplish these tasks. Here primary focus on ―Functions‖ and little attention on data. There are many high level languages like COBOL, FORTRAN, PASCAL, C used for conventional programming commonly known as POP. POP basically consists of writing a list of instructions for the computer to follow, and organizing these instructions into groups known as functions. A typical POP structure is shown in below: Normally a flowchart is used to organize these actions and represent the flow of control logically sequential flow from one to another. In a multi-function program, many important data items are placed as global so that they may be accessed by all the functions. Each function may have its own local data. Global data are more vulnerable to an in advent change by a function. In a large program it is very difficult to identify what data is used by which function. In case we need to revise an external data structure, we should also revise all the functions that access the data. This provides an opportunity for bugs to creep in. 6

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