深入理解多态及其在编程中的应用

多态是面向对象编程中的一个重要概念，它允许一个接口或基类以多种形态出现，即不同的子类可以有不同的行为。这种机制有助于代码的优化，避免冗余，同时增加程序的灵活性。

在现实生活中，多态表现为同一事物在不同条件下产生不同的结果。例如，动物在遇到危险时，有的会逃跑，有的会攻击。而在编程中，多态则体现在通过相同的接口调用不同对象的方法，从而执行不同的操作。

实现多态的关键在于继承和方法重写。通过继承，子类可以从父类继承属性和方法，而方法重写则允许子类根据需要改变从父类继承来的方法的行为。

主人类示例

public class Owner {
    // 为宠物治疗
    public void treat(Pet pet) {
        if (pet.getHealth() <50) {
            pet.goToHospital();
        }
    }

    // 给宠物喂食
    public void feed(Pet pet) {
        pet.eat();
    }
}

宠物基类

public class Pet {
    private String name = "Unnamed";
    private int health = 100;
    private int affection = 0;

    public Pet() {
        System.out.println("Base class no-arg constructor");
    }

    public Pet(String name) {
        this.name = name;
    }

    public Pet(String name, int health, int affection) {
        this.name = name;
        setHealth(health);
        setAffection(affection);
        System.out.println("Base class parameterized constructor");
    }

    public void setHealth(int health) {
        if (health <0 || health > 100) {
            System.out.println("Please enter a value between 0 and 100!");
            this.health = 60;
            return;
        }
        this.health = health;
    }

    public int getHealth() {
        return this.health;
    }

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

    public void setName(String name) {
        this.name = name;
    }

    public int getAffection() {
        return this.affection;
    }

    public void setAffection(int affection) {
        if (affection <0 || affection > 100) {
            System.out.println("Please enter a value between 0 and 100!");
            this.affection = 60;
            return;
        }
        this.affection = affection;
    }

    public void displayInfo() {
        System.out.println("Pet confession:\nMy name is " + this.name + ", health is " + this.health + ", and affection with the owner is " + this.affection + ".");
    }

    public void goToHospital() {}
}

宠物狗子类

public class Dog extends Pet {
    private String breed = "Clever Labrador Retriever";

    public Dog() {
        System.out.println("Subclass Dog no-arg constructor");
    }

    public Dog(String name, int health, int affection) {
        super(name, health, affection);
        System.out.println("Subclass Dog parameterized constructor");
    }

    public Dog(String name, int health, int affection, String breed) {
        this(name, health, affection);
        this.breed = breed;
        System.out.println("Subclass Dog four-parameter constructor");
    }

    public String getBreed() {
        return this.breed;
    }

    public void setBreed(String breed) {
        this.breed = breed;
    }

    @Override
    public void displayInfo() {
        super.displayInfo();
        System.out.println(", I am a: " + this.breed);
    }

    @Override
    public void goToHospital() {
        System.out.println("Injection, take medicine");
        setHealth(60);
    }
}

宠物企鹅子类

public class Penguin extends Pet {
    private String gender = "Q Baby";

    public Penguin() {
        System.out.println("Subclass Penguin no-arg constructor");
    }

    public Penguin(String name, int health, int affection, String gender) {
        super(name, health, affection);
        this.gender = gender;
        System.out.println("Subclass Penguin parameterized constructor");
    }

    public String getGender() {
        return this.gender;
    }

    public void setGender(String gender) {
        this.gender = gender;
    }

    @Override
    public void displayInfo() {
        super.displayInfo();
        System.out.println(", my gender is: " + this.gender);
    }

    @Override
    public void goToHospital() {
        System.out.println("Take medicine, rest");
        setHealth(60);
    }
}

宠物测试类

import java.util.Scanner;

public class TestPet {
    public static void main(String[] args) {
        Owner owner = new Owner();
        Scanner scanner = new Scanner(System.in);
        System.out.println("Welcome to the pet shop!");
        System.out.println("Please enter the name of the pet you want to adopt:");
        String name = scanner.next();
        System.out.println("Please enter the type of pet you want to adopt: 1. Dog 2. Penguin");
        int typeNo = scanner.nextInt();
        switch (typeNo) {
            case 1:
                System.out.println("Please enter the pet's health value:");
                int dHealth = scanner.nextInt();
                System.out.println("Please enter the pet's affection with the owner:");
                int dAffection = scanner.nextInt();
                System.out.println("Please enter the pet's breed:");
                String breed = scanner.next();
                Pet dog = new Dog(name, dHealth, dAffection, breed);
                dog.displayInfo();
                System.out.println("*************************");
                owner.treat(dog);
                System.out.println("*************************");
                dog.displayInfo();
                break;
            case 2:
                System.out.println("Please choose the pet's gender: 1. Female 2. Male");
                int genderId = scanner.nextInt();
                String gender = (genderId == 1) ? "Female" : "Male";
                System.out.println("Please enter the pet's health value:");
                int pHealth = scanner.nextInt();
                System.out.println("Please enter the pet's affection with the owner:");
                int pAffection = scanner.nextInt();
                Pet penguin = new Penguin(name, pHealth, pAffection, gender);
                penguin.displayInfo();
                System.out.println("*************************");
                owner.treat(penguin);
                System.out.println("*************************");
                penguin.displayInfo();
                break;
            default:
                System.out.println("We don't have that type of pet yet, please choose 1 or 2!");
                break;
        }
    }
}