💡Types of relationship in classes-
💡1- Is-a relationship-(INHERITANCE)
i.e- class bike, class pulser
Relationship- pulser is a bike
💡2- Has-a relationship-(ASSOCIATION)
i.e- class engine, class pulser
Relationship- pulser has a engine
💡INHERITANCE–
Inheritance is a concept where a class inherits data members and methods from another class.
💡1- Types of inheritance
💡(i) Single level inheritance
💡(ii) Multi level inheritance
💡(iii)Multiple inheritance
Note – We use interfaces to implement multiple inheritances, and implements keyword is used.
💡(iv) Hierarchical inheritance
💡(v) Hybrid inheritance –
Combination of any two or more inheritances.
for example –
(1) Single level Inheritance + multiple Inheritance
(2) Multi level Inheritance + multiple Inheritance
(3) Single level Inheritance + hierarchical Inheritance
(4) multi level Inheritance + hierarchical Inheritance
(5) multiple Inheritance + hierarchical Inheritance
💡ASSOCIATION–
Association is a concept where a class has reference of another class.
💡2- Types of association
💡(i) Aggregation
-> If we delete parent class, child class will still exist (loose coupled).
public class Organization {
private List<Person> employees;
}
public class Person {
}
💡(ii) Composition
-> If we delete parent class, child class will also be deleted (tight coupled).
public class Car {
private Engine engine;
public Car(){
engine = new Engine();
}
}
class Engine {
}
code samples are here
1-single level inheritance example- Program to extend class Parent C on class ExampleSingleLevel
package inheritance11;
class ParentC{
String name="paret class variable";
void show(){
System.out.println("Parent class method");
}
}
public class ExampleSingleLevel extends ParentC {
public static void main(String[] args) {
ExampleSingleLevel e1=new ExampleSingleLevel();
System.out.println(e1.name);
e1.show();
}
}
2- Multi level inheritance example-
package inheritance11;
class P1{
String a="grandparent variable"; \
void shw(){
System.out.println("grandparent method");
}
}
class P2 extends P1{
String n="parent variable";
void dsplay(){
System.out.println("parent method");
}
}
public class ExampleMultiLevel extends P2 {
public static void main(String[] args) {
ExampleMultiLevel e1=new ExampleMultiLevel();
System.out.println(e1.a);
e1.shw();
System.out.println(e1.n);
e1.dsplay();
}
}
package association12;
public class Engine {
private int engineCapacity;
private int engineSerialNumber;
public Engine(int engineCapacity, int engineSerialNumber) {
this.engineCapacity = engineCapacity;
this.engineSerialNumber = engineSerialNumber;
}
public int getEngineCapacity() {
return engineCapacity;
}
public int getEngineSerialNumber() {
return engineSerialNumber;
}
} b- Class AggregateCar
package association12;
public class AggregateCar {
private String make;
private int year;
private Engine engine;
public AggregateCar(String make, int year, Engine engine) {
this.make = make;
this.year = year;
this.engine = engine;
}
public String getMake() {
return make;
}
public int getYear() {
return year;
}
public Engine getEngine() {
return engine;
}
} c- Class Mainclass
package association12;
public class MainClass {
public static void main(String[] args) {
Engine engine=new Engine(10, 420);
AggregateCar agCar=new AggregateCar("Audi", 2016, engine);
}
} 2- Composition
a- Class Engine-
package association12;
public class Engine {
private int engineCapacity;
private int engineSerialNumber;
public Engine(int engineCapacity, int engineSerialNumber) {
this.engineCapacity = engineCapacity;
this.engineSerialNumber = engineSerialNumber;
}
public int getEngineCapacity() {
return engineCapacity;
}
public int getEngineSerialNumber() {
return engineSerialNumber;
}
} b- Class CompositeCar-
package association12;
public class CompositeCar {
private String make;
private int year;
private Engine engine;
public CompositeCar(String make, int year, int engineCapacity, int engineSerialNumber) { this.make=make;
this.year=year;
engine = new Engine(engineCapacity,engineSerialNumber);
}
public String getMake() { return make; }
public int getYear() { return year; }
public int getEngineSerialNumber() { return engine.getEngineSerialNumber(); }
public int getEngineCapacity() { return engine.getEngineCapacity(); } } c- Class MainClass
package association12;
public class MainClass {
public static void main(String[] args) {
Engine engine=new Engine(10, 420);
AggregateCar agCar=new AggregateCar("Audi", 2016, engine);
CompositeCar comCar=new CompositeCar("Ford", 2014, 20, 786);
}
} Interview Questions —
- What is difference between Inheritance and association ?
- Are private methods and private variables are get inherited ?
Core Java in 25 hours 