Java Object Oriented Programming

Java Object Oriented Programming

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  * Object Oriented Programmingis a paradigm that provides many concepts such as inheritance, data binding, polymorphism etc.
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  * It simplifies thesoftware development and maintenance by providing some concepts: Object Class Inheritance Polymorphism Abstraction Encapsulation
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  Any entity thathas state and behavior is known as an object. For example: chair, pen, table, keyboard, bike etc. It can be physical and logical. An object has three characteristics: state: represents data (value) of an object. behavior: represents the behavior (functionality) of an object such as deposit, withdraw etc. identity: Object identity is typically implemented via a unique ID. The value of the ID is not visible to the external user. But, it is used internally by the JVM to identify each object uniquely.
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  * Collection of objectsis called class. It is a logical entity. A class is a group of objects that has common properties. It is a template or blueprint from which objects are created. A class in java can contain: data member method constructor block class and interface
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  * When one objectacquires all the properties and behaviors of parent object i.e. known as inheritance. It provides code reusability. It is used to achieve runtime polymorphism.
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  * When one taskis performed by different ways i.e. known as polymorphism. For example: to convense the customer differently, to draw something e.g. shape or rectangle etc. In java, we use method overloading and method overriding to achieve polymorphism. Another example can be to speak something e.g. cat speaks meaw, dog barks woof etc.
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  * Hiding internal detailsand showing functionality is known as abstraction. For example: phone call, we don't know the internal processing. In java, we use abstract class and interface to achieve abstraction.
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  * Binding (or wrapping)code and data together into a single unit is known as encapsulation. For example: capsule, it is wrapped with different medicines. A java class is the example of encapsulation. Java bean is the fully encapsulated class because all the data members are private here.
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  * By using standardJava naming conventions, you make your code easier to read for yourself and for other programmers. Readability of Java program is very important. It indicates that less time is spent to figure out what the code does.
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  * Java follows camelcasesyntax for naming the class, interface, method and variable. If name is combined with two words, second word will start with uppercase letter always e.g. actionPerformed(), firstName, ActionEvent, ActionListener etc.
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  * If a classhave multiple methods by same name but different parameters, it is known as Method Overloading. There are two ways to overload the method in java: By changing number of arguments By changing the data type
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  * Constructor in javais a special type of method that is used to initialize the object. Rules for creating java constructor There are basically two rules defined for the constructor. Constructor name must be same as its class name Constructor must have no explicit return type
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  * Default constructor providesthe default values to the object like 0, null etc. depending on the type.
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  Java parameterized constructor Aconstructor that have parameters is known as parameterized constructor. Why use parameterized constructor? Parameterized constructor is used to provide different values to the distinct objects.
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  * There can bea lot of usage of java this keyword. In java, this is a reference variable that refers to the current object.
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  * If subclass (childclass) has the same method as declared in the parent class, it is known as method o Usage of Java Method Overriding Method overriding is used to provide specific implementation of a method that is already provided by its super class. Method overriding is used for runtime polymorphism Rules for Java Method Overriding method must have same name as in the parent class method must have same parameter as in the parent class. must be IS-A relationship (inheritance).