Methods
In Java programming, programming logic needs to be written inside methods:
- main() method is a method where the program execution starts and we can write programming logic inside the main() method
- Demonstrate creating multiple methods along with the below:
- Creating multiple methods along with main() method
- All the method should reside inside the Class
- main() method calling other method
- non-main() method calling other method
- method() calling other method multiple times
- Demonstrate single, multiple parameterized methods and passing arguments to those methods:
- Create a single parameterized method
- Create a multiple parameterized method
- Call the single and multiple parameterized methods by passing the arguments while calling
- Demonstrate returning the values back to the calling methods:
- Return nothing from a method
- Return int value from a method
- Return String value from a method
Variables
Variable is a name provided to a reserved memory location.
- There are two types of Variables:
- Local Variables
- A variable which is declared inside the method is called local variable
- Global Variables
- A variable which is declared inside the class but outside the method is called Global variable
- Scope of the variables
Classes and Objects
- Class encloses variables and methods
- Class is a template used for creating Objects
- Demonstrate creating a Class and use the Class as a template for creating Objects
- Create a Class having a main method say Demo
- Inside the same Java file create another Class named Car
- Create any variables inside the Car class say model, cost, color
- Create any methods inside the Car class say startCar(), stopCar(), carDetails()
- Create any objects using Car class
- Initialize and Access the variables & methods of Objects
- Object Creation Statement
- Car benz = new Car();
Constructors
Constructors are similar to methods, but have the below differences:
- Demonstrate the constructors having the below qualities:
- Constructors have the same name as Class name
- Constructors are automatically called when an object is created for the Class
- Constructors won’t have any return type – Return types like void, int etc won’t be available for constructors
- Empty hidden Constructor will be called, when an object is created for the Class not specified with explicit constructors
- Constructors simplify the initialization of variables
- Demonstrate initialization of variables without using constructors
- Demonstrate initialization of variables with constructors
this keyword
The purpose of the this keyword is to differentiate the instance variable with the parameterized variables of methods/constructors.
- Using this keyword with Methods
- Demonstrate the program which don’t use this keyword
- Demonstrate the advantage of using this keyword with methods
- Using this keyword with Constructors
- Generally required for constructors, as constructors are automatically called when objects are created and there by all the required variables will be initialized automatically
- Similar to methods.
Overloading
Duplicate methods/constructor names are allowed inside the same class, as long as their parameters count or declaration or order of parameters are different.
- method overloading
- Two or more methods having the same name can be created inside a single class as long as their parameters count or declaration are different.
- In this case, the methods are said to be overloaded and the concept is knows as Method overloading
- Compiler error will be displayed when more than one method has the same name
- Demonstrate how method overloading concept can avoid compiler error
- constructor overloading
- The same concept of method overloading when applied to constructors is known as constructor overloading
- In this case, the constructors are said to be overloaded and the concept is known as Constructor overloading
Inheritance
Inheritance is a mechanism in which one class acquires the properties (i.e. variables and methods) of another class
- The purpose of this Inheritance is to use the properties (i.e. methods and variables) inside a class instead of recreating the same properties again in new class.
- Child class acquires the properties (i.e. variables and methods) of Parent Class.
- Child class uses extends keyword to inherit the properties from parent class
- Demonstrate a child class which inherits the properties from Parent Class
- Child class can have specific properties (i.e. variables and methods) which are not available in the parent class
- Object created for parent class can access the variables and methods that are created in parent class only. It cannot access the child class properties.
- Object created for child class which is inheriting the parent class can access the variables and methods of both parent class and child class.
Overriding
When a method in the Child class (i.e. sub-class) is duplicate of a method in Parent class (i.e. super-class) , then the method in the sub-class is said to override the method in super-class.
- When we create an Object for Sub-class and call the overridden method, the method in the sub-class will be called
- Even though the name of the method in the sub-class has the same name as a method in super-class, if the type of parameters or number of parameters, then the method in the sub-class will overload the method in super-class instead of overriding
- Constructors cannot be overridden as the name of the constructor needs to be same as the name of the Class.
By,
Arun Motoori