Java class 3

What is Package? • A Java package is a mechanism for organizing Java classes into namespaces • Programmers use packages to organize classes belonging to the same category • Classes in the same package can access each other's package-access members Java Programming: OOP 2

Advantage of a Package • Programmers can easily determine that these classes are related • Programmers know where to find files of similar types • The names won't conflict • You can have define access of the types within the package Java Programming: OOP 3

Naming Convention of a Package • Package names are written in all lower case • Companies use their reversed Internet domain name to begin their package names— for example, com.example.mypackage for a package named mypackage created by a programmer at example.com Java Programming: OOP 4

Naming Convention of a Package If the domain name contains - i. a hyphen or a special character ii. if the package name begins with a digit, illegal character reserved Java keyword such as "int“ In this event, the suggested convention is to add an underscore Legalizing Package Names Domain Name Package Name Prefix hyphenated-name.example.org org.example.hyphenated_name example.int int_.example 123name.example.com com.example._123name Java Programming: OOP 5

Package Project package com.myproject; src com classes myproject com MyClass.java myproject MyClass.class Java Programming: OOP 6

• The child classes inherits all the attributes of the parent class • They also have their distinctive attributes Java Programming: OOP 8

Class Animal { // Type : Not Human // Lives : On Land // Gives Birth : } Class Aquatic extends Animal { // Lives : In Water // Gives Birth : } Java Programming: OOP 9

package com.edureka.animal; public class Animal { public String Type = "Not Human"; package com.edureka.animal; public String Lives = "In Water"; public class Aquatic extends Animal{ public void fun(){ String Lives = "In Water"; } public void fun(){ } System.out.println("defined here"); } } Java Programming: OOP 10

package com.edureka.animal; public class Main { public static void main(String[] args) { Aquatic ob = new Aquatic(); System.out.println(ob.Type); System.out.println(ob.Lives); ob.fun(); } } Java Programming: OOP 11

Java OOP • Create new object type with class keyword. • A class definition can contain: – variables (fields) – initialization code – methods Java Programming: OOP 13

An Example class package com.edureka.entity; // package public class Car{ //class declaration String name; String color; float weight; ... public void move(){ // method ... } }

Objects • Runtime representation of a class. • Objects hold state with variables • Objects do some work with methods. • Can be created during Runtime as follows : Car carRef = new Car(); carRef New Car() Object Reference Newly created Object

Methods • A method is a collection of statements that are grouped together to perform an operation. • A method takes some parameters, performs some computations and then optionally returns a value (or object).

Methods Methods have five components: • Modifiers Value to be returned Name of the Method • The return type return_type method_name (arg1, arg2, arg3) • The method name { ____ Body of the • The parameter list in ____ Method parenthesis } Any Number of Parameters • The method body, enclosed between braces

Method Overloading • The overloaded function must differ either by the number of arguments or operands or data types. • The same function name is used for various instances of function call

Method Overloading package com.edureka.animal; public class Animal { public void fun(){ System.out.println("Without Parameters"); package com.edureka.animal; } public class Aquatic extends Animal{ } public void fun(int num){ System.out.println ("The number passed is : " + num); } }

Method Overloading package com.edureka.animal; public class Main { public static void main(String[] args) { Aquatic ob = new Aquatic(); //without Parameters, defined in class Animal ob.fun(); //with Parameter, overloaded function in class Aquatic ob.fun(10); } }

Method Overriding • The implementation in the subclass overrides (replaces) the implementation in the superclass • It is done by providing a method that has same 1. name, same 2. parameters, and same 3. return type as the method in the parent class

Method Overriding package com.edureka.animal; public class Animal { int fun(int a, int b){ package com.edureka.animal; int c = a + b; return c; public class Aquatic extends Animal{ } int fun(int a, int b){ } System.out.println (“Sum by super class: " + super.fun(a, b)); int c = a * b; return c; } }

Method Overriding package com.edureka.animal; public class Main { public static void main(String[] args) { Aquatic ob = new Aquatic(); System.out.println(“Product by derived class : ”+ ob.fun(2,3)); } }

Modifiers • public: any method (in any class) can access the field. • protected: any method in the same package or any derived class can access the field. • private: only methods within the class can access the field. • default is that only methods in the same package can access the field. Java Programming: OOP 24

Java class 3

More Related Content

What's hot

Viewers also liked

Similar to Java class 3

More from Edureka!

Recently uploaded

Java class 3

Editor's Notes