Learn Java: Understanding Inheritance and Polymorphism

                                
// Parent Class
class Animal {
  // Animal class members
}
// Child Class
class Dog extends Animal {
  // Dog inherits traits from Animal 
  // additional Dog class members
}

                              

                                
// Parent Class
class Shape {
  public static void main(String[] args) {
    Square sq = new Square();
  }
}
// Child Class
class Square extends Shape {
  // Square inherits from Shape
}

                              

                                
// Parent class
class Animal {
  String sound;
  Animal(String snd) {
    this.sound = snd;
  }
}
// Child class
class Dog extends Animal {
  Dog() {
    super("woof");
  }
}

                              

                                
class Student {
  protected double gpa;
  // gpa can be accessed by subclasses
  final protected boolean isStudent() {
    return true;
  }
  // isStudent() cannot be overridden by subclasses
}

                              

                                
// Parent class
class Animal {
  public void greet() {
    System.out.println("The animal greets you.");
  }
}
// Child class
class Cat extends Animal {
  public void greet() {
    System.out.println("The cat meows.");
  }
}
class MainClass {
  public static void main(String[] args) {
    Animal myAnimal = new Animal();
    Animal myCat = new Cat();
    myAnimal.greet(); // Prints: The animal greets you.
    myCat.greet();    // Prints: The cat meows.
  }
}

                              

                                
// Parent class
class Animal {
  public void eat() {
    System.out.println("The animal is eating.");
  }
}
// Child class
class Dog extends Animal {
  @Override
  public void eat() {
    System.out.println("The dog is eating.");
  }
}

                              

                                
// Creating instances of different animals
Animal cat = new Cat();
Animal dog = new Dog();
Animal pig = new Pig();
// Storing them in an array
Animal[] animals = {cat, dog, pig};
// Iterating over the array and calling a method
for (Animal animal : animals) {
  animal.sound();
}

                              

                                
// Comparing two different objects
String a = new String("Dracaena");
String b = new String("Haworthia");
System.out.println(a.equals(b)); // Prints: false
// Comparing two identical objects
String c = new String("Haworthia");
System.out.println(b.equals(c)); // Prints: true

                              

                                
String str1 = new String("hello");
String str2 = new String("hello");
System.out.println(str1.equals(str2)); // Prints: true