Java Programming

As my AP Computer Science teacher eloquently said:

"You can't let strangers touch your private parts"

Therefore, if data was not hidden, a client class can modify all the variables(given that it is not a final constant) by simply calling:

className.variableName = newWrongData;

By using special methods to access the variables, the class can change its internal implementation, without breaking compatibility with other classes that are already using it.

Each Java object has varaibles - which in this case are called fields. They store information about the object. For example, a class to store a date might have "fields" to store the day, the month and the year. The values stored in these fields are collectively called the object's "state".

Eg If we consider a car which has lot of parts such as wheels steering DVD player etc.

We need to know how to use it. We need not know what is the

structure of all these parts to buy and drive a car.

Another eg is Television. The Television has lot of properties and behavoiurs like height width displayOn,displayOff etc and also it has chips and internal wires which enables the television's functions.

But for working the Television we don't need to know these internal things.

Java is an object oriented programming language. The main concepts used in Java are:

Class

Defines the abstract characteristics of a thing (object), including the thing's characteristics (its attributes, fields or properties) and the thing's behaviors (the things it can do, or methods, operations or features). One might say that a class is a blueprint or factory that describes the nature of something. For example, the class Dog would consist of traits shared by all dogs, such as breed and fur color (characteristics), and the ability to bark and sit (behaviors). Classes provide modularity and structure in an object-oriented computer program. A class should typically be recognizable to a non-programmer familiar with the problem domain, meaning that the characteristics of the class should make sense in context. Also, the code for a class should be relatively self-contained (generally using encapsulation). Collectively, the properties and methods defined by a class are called members.

Object

A pattern (exemplar) of a class. The class of Dog defines all possible dogs by listing the characteristics and behaviors they can have; the object Lassie is one particular dog, with particular versions of the characteristics. A Dog has fur; Lassie has brown-and-white fur.

Instance

One can have an instance of a class or a particular object. The instance is the actual object created at runtime. In programmer jargon, the Lassie object is an instance of the Dog class. The set of values of the attributes of a particular object is called its state. The object consists of state and the behaviour that's defined in the object's class.

Method

An object's abilities. In language, methods (sometimes referred to as "functions") are verbs. Lassie, being a Dog, has the ability to bark. So bark() is one of Lassie's methods. She may have other methods as well, for example sit() or eat() or walk() or save_timmy(). Within the program, using a method usually affects only one particular object; all Dogs can bark, but you need only one particular dog to do the barking.

Message passing

"The process by which an object sends data to another object or asks the other object to invoke a method." Also known to some programming languages as interfacing. For example, the object called Breeder may tell the Lassie object to sit by passing a "sit" message which invokes Lassie's "sit" method. The syntax varies between languages, for example: [Lassie sit] in Objective-C. In Java, code-level message passing corresponds to "method calling". Some dynamic languages use double-dispatch or multi-dispatch to find and pass messages.

Inheritance

"Subclasses" are more specialized versions of a class, which inherit attributes and behaviors from their parent classes, and can introduce their own.

For example, the class Dog might have sub-classes called Collie, Chihuahua, and GoldenRetriever. In this case, Lassie would be an instance of the Collie subclass. Suppose the Dog class defines a method called bark() and a property called furColor. Each of its sub-classes (Collie, Chihuahua, and GoldenRetriever) will inherit these members, meaning that the programmer only needs to write the code for them once.

Each subclass can alter its inherited traits. For example, the Collie class might specify that the default furColor for a collie is brown-and-white. The Chihuahua subclass might specify that the bark() method produces a high pitch by default. Subclasses can also add new members. The Chihuahua subclass could add a method called tremble(). So an individual chihuahua instance would use a high-pitched bark() from the Chihuahua subclass, which in turn inherited the usual bark() from Dog. The chihuahua object would also have the tremble() method, but Lassie would not, because she is a Collie, not a Chihuahua. In fact, inheritance is an "a... is a" relationship between classes, while instantiation is an "is a" relationship between an object and a class: a Collie is a Dog ("a... is a"), but Lassie is a Collie ("is a"). Thus, the object named Lassie has the methods from both classes Collie and Dog.

Multiple inheritance is inheritance from more than one ancestor class, neither of these ancestors being an ancestor of the other. For example, independent classes could define Dogs and Cats, and a Chimera object could be created from these two which inherits all the (multiple) behavior of cats and dogs. This is not always supported, as it can be hard both to implement and to use well.

Abstraction

Abstraction is simplifying complex reality by modelling classes appropriate to the problem, and working at the most appropriate level of inheritance for a given aspect of the problem.

For example, Lassie the Dog may be treated as a Dog much of the time, a Collie when necessary to access Collie-specific attributes or behaviors, and as an Animal (perhaps the parent class of Dog) when counting Timmy's pets.

Abstraction is also achieved through Composition. For example, a class Car would be made up of an Engine, Gearbox, Steering objects, and many more components. To build the Car class, one does not need to know how the different components work internally, but only how to interface with them, i.e., send messages to them, receive messages from them, and perhaps make the different objects composing the class interact with each other.

Encapsulation

Encapsulation conceals the functional details of a class from objects that send messages to it.

For example, the Dog class has a bark() method. The code for the bark() method defines exactly how a bark happens (e.g., by inhale() and then exhale(), at a particular pitch and volume). Timmy, Lassie's friend, however, does not need to know exactly how she barks. Encapsulation is achieved by specifying which classes may use the members of an object. The result is that each object exposes to any class a certain interface - those members accessible to that class. The reason for encapsulation is to prevent clients of an interface from depending on those parts of the implementation that are likely to change in future, thereby allowing those changes to be made more easily, that is, without changes to clients. For example, an interface can ensure that puppies can only be added to an object of the class Dog by code in that class. Members are often specified as public, protected or private, determining whether they are available to all classes, sub-classes or only the defining class. Some languages go further: Java uses the default access modifier to restrict access also to classes in the same package, C# and VB.NET reserve some members to classes in the same assembly using keywords internal (C#) or Friend (VB.NET), and Eiffel and C++ allow one to specify which classes may access any member.

Polymorphism

Polymorphism allows the programmer to treat derived class members just like their parent class' members. More precisely, Polymorphism in object-oriented programming is the ability of objects belonging to different data types to respond to method calls of methods of the same name, each one according to an appropriate type-specific behavior. One method, or an operator such as +, -, or *, can be abstractly applied in many different situations. If a Dog is commanded to speak(), this may elicit a bark(). However, if a Pig is commanded to speak(), this may elicit an oink(). They both inherit speak() from Animal, but their derived class methods override the methods of the parent class; this is Overriding Polymorphism. Overloading Polymorphism is the use of one method signature, or one operator such as "+", to perform several different functions depending on the implementation. The "+" operator, for example, may be used to perform integer addition, float addition, list concatenation, or string concatenation. Any two subclasses of Number, such as Integer and Double, are expected to add together properly in an OOP language. The language must therefore overload the addition operator, "+", to work this way. This helps improve code readability. How this is implemented varies from language to language, but most OOP languages support at least some level of overloading polymorphism. Many OOP languages also support Parametric Polymorphism, where code is written without mention of any specific type and thus can be used transparently with any number of new types. Pointers are an example of a simple polymorphic routine that can be used with many different types of objects.

Decoupling

Decoupling allows for the separation of object interactions from classes and inheritance into distinct layers of abstraction. A common use of decoupling is to polymorphically decouple the encapsulation, which is the practice of using reusable code to prevent discrete code modules from interacting with each other. However, in practice decoupling often involves trade-offs with regard to which patterns of change to favor. The science of measuring these trade-offs in respect to actual change in an objective way is still in its infancy.

Note: Not all of the above concepts are to be found in all object-oriented programming languages, and so object-oriented programming that uses classes is called sometimes class-based programming. In particular, prototype-based programming does not typically use classes. As a result, a significantly different yet analogous terminology is used to define the concepts of object and instance.

Advantage:

1.) Java program are platform independent, it can run on any PC or any operation system.

2.) It is dynamic, simple and robust.

3.) It is purely OOPS language having all the OOPS concept.

Disadvantage:

1.) It takes more time to execute then " C language" as it runs first on JVM (Java Virtual Machine).

2.) More memory consuming then other languages.

FUNCTION OVERLOADING:

- when we define two functions with same name,in same class(may be) distinguished by their signatures

- resolved at compile time

- same method bt different parameters in each of them

FUNCTION OVERRIDING:

- when we redifine a function which is already defined in parent class

- resolved at run time

- changing the existing method

Yes, Java supports multidimensional Arrays.

Syntax is

int[ ][ ] aryNumbers = new int[x][y];

x represents number of rows

y represents number of columns

// Import Library

import javax.swing.*;

//Beginning class Diamond

public class Diamond

{

//Main method

public static voidmain(String[] args)

{

//Declaring Variables

String strRow = null;

double dblRow = 0;

//GUI user input

strRow = JOptionPane.showInputDialog("Please enter an ODD number ");

dblRow = Integer.parseInt(strRow);

//validate a odd number

if ((dblRow % 2)== 0)

//if not an odd number user is advised

JOptionPane.showMessageDialog(null, "The number entered is not an ODD number. Please, try again");

//Building diamond

else

{

//setting up first 1/2 of the diamond - rows

for(int a=1; a<(dblRow/2+.5); a++ )

{

//Assigning empty spaces from right side

for (int b=1; b<(dblRow/2+1.5)-a; b++)

{

System.out.print(" ");

}

//filling out with *

for(int c=0; c<(a*2)-1; c++)

System.out.print("*");

System.out.println();

}

//Creating middle line of the diamond

for(int d=1; d

{

System.out.print("=");

}

System.out.println();

//setting our second 1/2 of the diamond - rows

for(int a=1; a<(dblRow/2+.5); a++ )

{

//Assigning empty spaces from right side in second part of diamond

for(int c=0;c

System.out.print(" ");

//filling out with *

for(int b=1; b

{

System.out.print("*");

}

System.out.println();

}

}

}

}