The document discusses Java packages and some key concepts around them: 1. A Java package is a mechanism for organizing Java classes into namespaces. Classes in the same package can access each other's package-access members. 2. Programmers use packages to organize classes belonging to the same category. This makes it easy to determine related classes and find files of similar types. Packages also prevent naming conflicts. 3. By convention, package names are written in all lowercase and company names are included in the package name based on the reversed domain name, such as "com.example.mypackage" for a package created by example.com.

1. Java Review
(Packages)

2. 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

3. 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

4. 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

5. 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

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

7. Inheritance

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

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

10. 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

11. 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

12. Java Methods & Classes

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

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

15. 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

16. 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).

17. 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

18. 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

19. 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);
}
}

20. 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);
}
}

21. 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

22. 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;
}
}

23. 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));
}
}

24. 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

25. •Q& A..?

26. Thanks..!