Java Inheritance
Java Inheritance defines an is-a relationship between a superclass and its subclasses. This means that an object of a subclass can be used wherever an object of the superclass can be used. Class Inheritance in java mechanism is used to build new classes from existing classes. The inheritance relationship is transitive: if class x extends class y, then a class z, which extends class x, will also inherit from class y.
Inheritance
- When a "Is-A" relationship exists between two classes we use Inheritance
- The parent class is termed super class and the inherited class is the sub class
- The keyword extends is used by the sub class to inherit the features of super class
- Inheritance is important since it leads to reusability of code
Single Inheritance or or One level Inheritance.
When a subclass is derived simply from it's parent class then this mechanism is known as simple inheritance. In case of simple inheritance there is only a sub class and it's parent class. It is also called single inheritance or one level inheritance.
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class A {
int x;
int y;
int get(int p, int q){
x=p; y=q; return(0);
}
void Show(){
System.out.println(x);
}
}
class B extends A{
public static void main(String args[]){ A a = new A();
a.get(5,6);
a.Show();
}
void display(){
System.out.println("B");
}
}
Multilevel Inheritance
It is the enhancement of the concept of inheritance. When a subclass is derived from a derived class then this mechanism is known as the multilevel inheritance. The derived class is called the subclass or child class for it's parent class and this parent class works as the child class for it's just above ( parent ) class. Multilevel inheritance can go up to any number of level.
class A {
int x;
int y;
int get(int p, int q){
x=p; y=q; return(0);
}
void Show(){
System.out.println(x);
}
}
class B extends A{
void Showb(){
System.out.println("B");
}
}

class C extends B{
void display(){
System.out.println("C");
}
public static void main(String args[]){
A a = new A();
a.get(5,6);
a.Show();
}
}
this and super keywords
The two keywords, this and super to help you explicitly name the field or method that you want. Using this and super you have full control on whether to call a method or field present in the same class or to call from the immediate superclass. This keyword is used as a reference to the current object which is an instance of the current class. The keyword super also references the current object, but as an instance of the current class's super class. The this reference to the current object is useful in situations where a local variable hides, or shadows, a field with the same name. If a method needs to pass the current object to another method, it can do so using the this reference. Note that the this reference cannot be used in a static context, as static code is not executed in the context of any object.
Example
class Incrementer {

int i = 0;
Incrementer increment() {
i++;
return this;
}
void print() {
System.out.println("i = " + i);
}
}

public class IncrementerDemo extends Incrementer {

public static void main(String[] args) {
Incrementer x = new Incrementer();
x.increment().increment().increment().print();
}
}
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