Inheritance,Abstract Class,Interfaces,Polymorphism
Inheritance:
Example->http://www.eclipse.org/eclipselink/documentation/2.5/concepts/img/javainhr.gif
|
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 |
1. The objective of inheritance is reusability. 2. The process of acquiring the methods and variables from SuperClass(RemoteWebDriver) to SubClass(FirefoxDriver) is called Inheritance. FirefoxDriver driver = new FirefoxDriver(); driver.get("http://www.google.com"); 3. Inheritance is achieved between two classes using the keyword called 'extends'. So, from now onwards 'extends' means inheritance. Ex: Car is-a Vehicle Vehicle is superclass Car is subclass public class FirefoxDriver extends RemoteWebDriver 4. Single Inheritance is between two classes is achieved using the extends keyword 5. Multilevel Inheritance means the subclass(child) can access super class(Father) and super class can access super class of (Father) (GrandFather) also. 6. Multiple Inheritance: In java we cannot extend more than one class at a time. Muliple classes cannot be inherited at the same time. So, multiple inheritance is not supported in java. ClassC extends ClassB,ClassA //Not Valid in java Diamond Problem in java. public class Object { public int hashcode() { return 1; } } public class RWD extends Object { public void get(String url) { } } public class FirefoxDriver extends RWD { } public class IndeedTests { main() { System.setPRoperty(); FirefoxDriver driver = new FirefoxDriver(); driver.get(""); } } |
Abstract Class:
|
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 |
Methods: In java they are two types of methods a. concrete methods: Methods which are having body are called as Concrete Methods //Concrete Method or complete Method public int add(int a,int b) { //Method body } If a method has curly braces mean, it has body.. it is implemented. b. abstract methods: Methods which are not having body are called as Abstract Methods //Abstract Method or In-Complete Method public abstract int add(int a, int b); Points to be Noted for Abstract classes: 1. The abstract method should be declared with keyword abstract. //InComplete Class public abstract class Car { //Concrete Method public void gears() { } //abstract Method public abstract void engine(); } 2. If a class contains one abstract method, then the class should be declared as abstract. 3. Inside a abstract class, we can develop both abstract and concrete method. Ex: abstract - engine,concrete-brakes() 4. If a class is declared as abstract its not mandatory to develop abstract methods.*************** 5. We cannot create an instance/object of abstract class, hence we cannot access non-static members of the abstract class.-Ex: we cannot invoke wheeling 6. The static members of the abstract class can be referred using class name. Ex: By.name(""),By.className("") non-static at the object level. static at the class level. 7. A SubClass inheriting an abstract class should override all the abstract methods of abstract class. Ex: engine Summary: static methods are invoked using className non-static concrete methods using inheritance invoked within subclass abstract methods using inheritance implemented in the subclass and invoked within subclass.. |
Interface:
|
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 |
An interface is a reference type in Java, it is similar to class, it is a collection of abstract methods. A class implements an interface, thereby inheriting the abstract methods of the interface. Along with abstract methods an interface may also contain constants and static methods. It doesnt contain non-static methods final int i=10; i=15; // Error final variables are constants.. public class Shapes // circle,cylinder,square,rectangle { public abstract void area(); public abstract void noofsides(); } interface Shapes { void area(); public abstract void noofsides(); } Points to be noted for interfaces: 1. An interface is a group of related methods with empty bodies.Ex: Abstract Methods 2. All interface abstract methods are by default/optional abstract and public. Ex: Default means hear it is optional Ex: void area() or public abstract void area() 3. We cannot develop non static concrete methods inside interfaces. 4. So, in interfaces the methods are only public ,abstract,static. No other keywords are allowed. 5. Interface variables has to be initialized at the time of declaration. 6. All the interface variables are by default public static final. 7. Interfaces are going to be implemented by subclass using a keyword called 'implements' 8. A SubClass implmenting an interface should implement all the abstract methods of the interface. 9. A class can implement multiple interfaces. Mulitiple inheritance is achieved using interfaces ClassA implements interfaceA,interfaceB { } ------------------------------------------------------------------------------------------------------ Implementing an interface by a class can be written as follows: Interface refvar = new ClassName(); WebDriver driver = new FirefoxDriver(); WebDriver driver = new ChromeDriver(); WebDriver driver = new InternetExplorerDriver(); final variables are constants final int i =5; i=6; //not possible.. final class cannot be inherited. Example: public final class System{} public class Example extends System{} // not possible final methods cannot be overridden. |
Polymorphism:
|
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 |
Polymorphism its an most imp oops concept. Polymorphism means existence of Methods and objects in many forms.2 types of polymorphism in java. Note: Compile Time checks for syntax. Run Time memory allocation happens for objects,variables. 1. Compile Time/Static Binding/Method Overloading: ------------------------------------------------------- Existence of two or more methods with in a class which are having same name but having parameters differ in the following way: a. Type of Arguments public void area(int a){} public void area(float a){} b. Position of Arguments public void area(int a,float b){} public void area(float a,int b){} c. No of Arguments public void area(int a){} public void area(int a,int b){} Then we should call these methods are overloaded methods. Method invocation is mapped to method impl during compile Time. Static Binding means the mapping is fixed it will not change during run time. Method Overloading happens with in a class. for priting integer-> int i =5; System.out.println(i); for priting float-> float f =3.5f; System.out.println(f); Constructor Overloading: -------------------------- Constructor is special type of method which is having same name as the classname, but it doesnt have any returntype. public class Student { Student()//Default Constructor { } Student(int i )//Parameterized Constructor { } Student(float f )//Parameterized Constructor { } } 2. Run Time/Dynamic Binding/Method Overriding ------------------------------------------------ If a method which is having same name and same arguments available in superclass and subclass are known are Overriden methods. Method invoication mappedto Method implementation is changed during compile to run time. So, we call this as run time polymorphism and Dynamic Binding. Note: A SuperClass can store its subclass object. Animal a = new Bird(); Bird is-a Animal. 'is-a' an inheritance relationship. public class Animal{} public class Bird extends Animal{ main() { Animal a = new Bird(); } } -------------------------------------------------------------------------------------------------------- Overview of System.out.println() public class System { static PrintStream out =new PrintStream(); } public class PrintStream { void println(int i) { } } |
Hello there, Where do we use the OOPS concepts – Polymorphism, Abstraction and Encapsulation in Selenium ? Please share with examples.