Figure 6.1 Animal Kingdom in Java

abstract class Animal {abstract public void speak();

}

class Bird extends Animal {public void speak() { System.out.println("twitter"); }

}

class Mammal extends Animal {public void speak() { System.out.println("can't speak"); }public void bark() { System.out.println("can't bark"); }

}

class Cat extends Mammal {public void speak() { System.out.println("meow"); }public void purr() { System.out.println("purrrrr"); }

}

class Dog extends Mammal {public void speak() { System.out.println("wouf"); }public void bark() { System.out.println("wouf"); }

}

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