super_keyword.md

super keyword

super is a keyword created by JVM and supplied to each and every Java program to differentiate between BaseClass feature and DerivedClass feature

If BaseClass feature and DerivedClass feature is same, then super keyword is used

super at variable level

If data member of BaseClass and DerivedClass are same then JVM gets an ambiguity. To solve the above problem super keyword is used

class A{
    int a;
}
class B extends A{
    int a;
    int b;
    void set(int x, int y){
        // a = x;  // base class variable
        super.a = x;  // parent class variable
        a = y;  // child class variable
    }
    void add(){
        // b = a + a;  // adds the a's of 
        b = super.a + a;  // ParentClassVar + ChildClassVar
        System.out.println(b);
    }
}
class Demo{
    public static void main(String args[]){
        B obj = new B();
        obj.set(100, 200);
        obj.add();
    }
}

super at method level

code here

super at constructor level

Whenever we create an object of ChildClass then first memory space for BaseClass is created

First the data member of BaseClass will be initialized then data member of ChildClass will be initialized

So, constructor of BaseClass is executed first and then constructor of ChildClass would be executed

class A{  // constructor
    A(){
        System.out.println("Base Class");
    }
}
class B extends A{
    B(){
        System.out.println("Child Class");
    }
}
class Demo{
    public static void main(String args[]){
        B obj = new B();
    }
}

class A{
    A(){
        System.out.println("Base default");
    }
    A(int a){
        System.out.println("Base Class Parameter");
    }
class B extends A{
    B(){
        Super(100);
        System.out.println("Child default");
    }
    B(int a){
        this(100, 200)
        System.out.println("Child single parameter");
    }
    B(int x, int y){
        System.out.println("Child double parameter");
    }

}
}
class Demo{
    public static void main(String args[]){
        B obj = new B(100);
        B obj = new B();
    }
}
/* Output
Base default
Child double parameter
Child single parameter
Base Class Parameter
Child default
*/