Скачать или смотреть Scala For Apache Spark|Session36|Scala Polymorphism|Method Overriding|Manohar Papasani

Scala Method Overriding

Overring happens between parent and child class.
We can override methods and variables.

Declaring method of parent class in child class with same signature but with different implementation.

If we are not satisfied with the implementation of parent class method,we override it in subclass with current requirement.

While overriding we should use "override" with sub class method.

In OOP a super class reference can refer to a sub class object,this is basis for "loose coupling".

Note:It is mandatory to use override keyword if we are overrding instance concrete method.

A sub class reference cannot refer to super class object,we get compilation error.
if we try to apply casting and continue it leads to ClassCastException.


//overriding
class A1 {
//overridden
def m1(): Unit = {
println("Hello")
}
}
class B1 extends A1 {
//overriding
override def m1(): Unit = {
println("Hi")
}

}

object Test {
def main(args: Array[String]): Unit = {
var a = new A1()
a.m1() //Hello

var b = new B1()
b.m1() //hi

var a1:A1 = new B1()
a1.m1()

}

}