Types of Inheritance

1// Single Inheritance: One parent, one child
2public class Animal {
3    public void eat() {
4        System.out.println("Eating...");
5    }
6}
7
8public class Dog extends Animal {  // Dog has ONE parent
9    public void bark() {
10        System.out.println("Barking...");
11    }
12}
13
14Dog dog = new Dog();
15dog.eat();   // From Animal
16dog.bark();  // From Dog

1// Multilevel Inheritance: Chain of inheritance
2public class Animal {
3    public void eat() {
4        System.out.println("Eating...");
5    }
6}
7
8public class Mammal extends Animal {
9    public void breathe() {
10        System.out.println("Breathing air...");
11    }
12}
13
14public class Dog extends Mammal {
15    public void bark() {
16        System.out.println("Barking...");
17    }
18}
19
20// Chain: Animal → Mammal → Dog
21Dog dog = new Dog();
22dog.eat();     // From Animal (grandparent)
23dog.breathe(); // From Mammal (parent)
24dog.bark();    // From Dog (self)
25
26// instanceof checks
27System.out.println(dog instanceof Dog);    // true
28System.out.println(dog instanceof Mammal); // true
29System.out.println(dog instanceof Animal); // true
30System.out.println(dog instanceof Object); // true

1// Hierarchical Inheritance: Multiple children, one parent
2public class Vehicle {
3    protected String brand;
4    
5    public void start() {
6        System.out.println("Vehicle starting");
7    }
8}
9
10public class Car extends Vehicle {
11    public void drive() {
12        System.out.println("Car driving on road");
13    }
14}
15
16public class Motorcycle extends Vehicle {
17    public void ride() {
18        System.out.println("Motorcycle riding");
19    }
20}
21
22public class Truck extends Vehicle {
23    public void haul() {
24        System.out.println("Truck hauling cargo");
25    }
26}
27
28// All inherit from Vehicle
29Vehicle v1 = new Car();
30Vehicle v2 = new Motorcycle();
31Vehicle v3 = new Truck();
32
33// Polymorphic array
34Vehicle[] vehicles = {v1, v2, v3};
35for (Vehicle v : vehicles) {
36    v.start();  // All can start
37}

1// Multiple Inheritance - Via Interfaces Only!
2
3// ✗ This is NOT allowed:
4// class Child extends Parent1, Parent2 {}  // ERROR!
5
6// ✓ Multiple interfaces ARE allowed:
7interface Flyable {
8    void fly();
9}
10
11interface Swimmable {
12    void swim();
13}
14
15interface Walkable {
16    void walk();
17}
18
19// Duck can implement multiple interfaces
20public class Duck implements Flyable, Swimmable, Walkable {
21    @Override
22    public void fly() {
23        System.out.println("Duck flying");
24    }
25    
26    @Override
27    public void swim() {
28        System.out.println("Duck swimming");
29    }
30    
31    @Override
32    public void walk() {
33        System.out.println("Duck walking");
34    }
35}
36
37// Can extend class AND implement interfaces
38public class Bird {
39    public void eat() {
40        System.out.println("Bird eating");
41    }
42}
43
44public class Eagle extends Bird implements Flyable {
45    @Override
46    public void fly() {
47        System.out.println("Eagle soaring");
48    }
49}