Object Oriented Programming

What are the two ways to method overload?

1) Changing the number of parameters 2) Changing the data type

Advantages of OOP (2)

1) OOPs makes development and maintenance easier whereas in a procedure-oriented programming language it is not easy to manage if code grows as project size increases. 2) OOPs provides data hiding whereas in a procedure-oriented programming language a global data can be accessed from anywhere.

Class

A class, in the context of Java, are templates that are used to create objects, and to define object data types and methods. Core properties include the data types and methods that may be used by the object A class can also be defined as a blueprint from which you can create an individual object. Class doesn't consume any space.

Parameratized Constructor

A constructor which has a specific number of parameters is called a parameterized constructor. The parameterized constructor is used to provide different values to the distinct objects. However, you can provide the same values also.

Rules of Method Overriding (3)

The method must have the same name as in the parent class The method must have the same parameter as in the parent class. There must be an IS-A relationship (inheritance).

When is a constructor called?

When an object is created, compiler makes sure that constructors for all of its subobjects (its member and inherited objects) are called. If members have default constructors or constructor without parameter then these constructors are called automatically, otherwise parameterized constructors can be called using initializer list. Note: It is called constructor because it constructs the values at the time of object creation. It is not necessary to write a constructor for a class. It is because java compiler creates a default constructor if your class doesn't have any.

Object Example

A dog is an object because it has states like color, name, breed, etc. as well as behaviors like wagging the tail, barking, eating, etc.

Object

Any entity that has state and behavior is known as an object. For example a chair, pen, table, keyboard, bike, etc. It can be physical or logical. An Object can be defined as an instance of a class. An object contains an address and takes up some space in memory. Objects can communicate without knowing the details of each other's data or code. The only necessary thing is the type of message accepted and the type of response returned by the objects.

Terms used in inheritance (4)

Class: A class is a group of objects which have common properties. It is a template or blueprint from which objects are created. Sub Class/Child Class: Subclass is a class which inherits the other class. It is also called a derived class, extended class, or child class. Super Class/Parent Class: Superclass is the class from where a subclass inherits the features. It is also called a base class or a parent class. Reusability: As the name specifies, reusability is a mechanism which facilitates you to reuse the fields and methods of the existing class when you create a new class. You can use the same fields and methods already defined in the previous class.

Constructor vs Method (5 of each)

Constructor : A constructor is used to initialize the state of an object. A constructor must not have a return type. The constructor is invoked implicitly. The Java compiler provides a default constructor if you don't have any constructor in a class. The constructor name must be same as the class name. Method : A method is used to expose the behavior of an object. A method must have a return type. The method is invoked explicitly. The method is not provided by the compiler in any case. The method name may or may not be same as class name.

Rules to remember when creating a constructor (3)

Constructor name must be the same as its class name A Constructor must have no explicit return type A Java constructor cannot be abstract, static, final, and synchronized

Advantages of Inheritance (2)

For Method Overriding (so runtime polymorphism can be achieved). For Code Reusability.

Method Overloading

If a class has multiple methods having same name but different in parameters, it is known as Method Overloading. If we have to perform only one operation, having same name of the methods increases the readability of the program. Suppose you have to perform addition of the given numbers but there can be any number of arguments, if you write the method such as a(int,int) for two parameters, and b(int,int,int) for three parameters then it may be difficult for you as well as other programmers to understand the behavior of the method because its name differs.

Method Overriding

If subclass (child class) has the same method as declared in the parent class, it is known as method overriding in Java. In other words, If a subclass provides the specific implementation of the method that has been declared by one of its parent class, it is known as method overriding.

Constructor

In Java, a constructor is a block of codes similar to the method. It is called when an instance of the object is created, and memory is allocated for the object. It is a special type of method which is used to initialize the object.

Constructor Overloading

In Java, a constructor is just like a method but without return type. It can also be overloaded like Java methods. Constructor overloading in Java is a technique of having more than one constructor with different parameter lists. They are arranged in a way that each constructor performs a different task. They are differentiated by the compiler by the number of parameters in the list and their types.

Inheritance

Inheritance in Java is a mechanism in which one object acquires all the properties and behaviors of a parent object. It is an important part of OOPs (Object Oriented programming system). The idea behind inheritance in Java is that you can create new classes that are built upon existing classes. When you inherit from an existing class, you can reuse methods and fields of the parent class. Moreover, you can add new methods and fields in your current class also. Inheritance represents the IS-A relationship which is also known as a parent-child relationship.

Usage for Method Overriding (2)

Method overriding is used to provide the specific implementation of a method which is already provided by its superclass. Method overriding is used for runtime polymorphism

Is multiple inheritance available in Java?

No

Can a static method be overridden?

No, a static method cannot be overridden. It can be proved by runtime polymorphism, so we will learn it later. It is because the static method is bound with class whereas instance method is bound with an object. Static belongs to the class area, and an instance belongs to the heap area.

Polymorphism (2)

Polymorphism is the ability of an object to take on many forms. The most common use of polymorphism in OOP occurs when a parent class reference is used to refer to a child class object. Any Java object that can pass more than one IS-A test is considered to be polymorphic. In Java, all Java objects are polymorphic since any object will pass the IS-A test for their own type and for the class Object.

Default Constructor

The default constructor is a no-args constructor that the Java compiler inserts on your behalf; it contains a default call to super(); which is the default behavior. If you implement any constructor then you no longer receive a default constructor. Note : If there is no constructor in the class, the compiler adds a default constructor