What approaches and techniques of polymorphism are available in Java, and how are they implemented?

In Java, polymorphism is implemented in two main ways:

1. Runtime polymorphism (dynamic polymorphism) — achieved through method overriding. When you have a reference to a base class but the object actually belongs to a derived class, the version of the method in the derived class is called.

class Animal {
    void sound() {
        System.out.println("Some sound");
    }
}

class Dog extends Animal {
    @Override
    void sound() {
        System.out.println("Bark");
    }
}

Animal a = new Dog();
a.sound(); // Will output "Bark"

2. Compile-time polymorphism (static polymorphism) — implemented through method overloading, where multiple methods in the same class have the same name but different parameters.

class Calculator {
    int add(int a, int b) {
        return a + b;
    }
    double add(double a, double b) {
        return a + b;
    }
}

Thus, Java supports polymorphism through inheritance and interfaces, allowing objects of different classes to use the same interface with different implementations.