A silly inheritance and polymorphism example.

DogHuman.java

public class DogHuman extends SuperHuman {
    public DogHuman(String name, int age) {
        super(name, age);
    }

    @Override
    public String greet() {
        return "Woof woof, woof woof, woof woof, woof woof, woof woof";
    }

    /*
    Returns the DogHuman's age in dog years.
     */
    @Override
    public int getAge() {
        return super.getAge() * 15;
    }
}

HumanRunner.java

import java.util.Random;

public class HumanRunner {
    public static void main(String[] args) {
        Random random = new Random();
        SuperHuman superHuman = new SuperHuman("John", random.nextInt(100) + 1);
        SubHuman subHuman = new SubHuman("Glug", random.nextInt(100) + 1);
        int dogHumanAge = random.nextInt(7) +1;
        DogHuman dogHuman = new DogHuman("Dog", dogHumanAge);
        System.out.printf("The human says: \"%s\"%n", superHuman.greet());
        System.out.printf("%s says: \"%s\"%n", subHuman.getName(), subHuman.greet());
        System.out.printf("The dog says: \"%s\".%n",dogHuman.greet());
        System.out.printf("%s is %d years old, but in dog years that's %d.%n",
                dogHuman.getName(), dogHumanAge, dogHuman.getAge());
    }
}

SubHuman.java

public class SubHuman extends SuperHuman{
    public SubHuman(String name, int age) {
        super(name, age);
    }

    @Override
    public String greet() {
        return "Grrrow, ug slrowl slurp";
    }
}

SuperHuman.java

public class SuperHuman {
    private String name;
    private int age;

    public SuperHuman(String name, int age) {
        this.name = name;
        this.age = age;
    }

    protected String getName() {
        return this.name;
    }

    protected int getAge() {
        return this.age;
    }

    public String greet() {
        return String.format("Hello, my name is %s. I am %d years old.", this.name, this.age);
    }
}