java面向对象的三大特性

// 面向对象的三大特性：封装、继承、多态

// 1. 封装 (Encapsulation)
class Person {
    // 私有属性，外部无法直接访问
    private String name;
    private int age;

    // 提供公共方法来访问私有属性
    public String getName() {
        return name;
    }

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

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        if (age > 0 && age < 120) {
            this.age = age;
        } else {
            System.out.println("年龄输入不合法");
        }
    }
}

// 2. 继承 (Inheritance)
class Student extends Person {
    private String studentId;

    public String getStudentId() {
        return studentId;
    }

    public void setStudentId(String studentId) {
        this.studentId = studentId;
    }

    // 可以重写父类的方法
    @Override
    public String toString() {
        return "Student{name='" + super.getName() + "', age=" + super.getAge() + ", studentId='" + studentId + "'}";
    }
}

// 3. 多态 (Polymorphism)
class Animal {
    public void makeSound() {
        System.out.println("动物发出声音");
    }
}

class Dog extends Animal {
    @Override
    public void makeSound() {
        System.out.println("汪汪汪");
    }
}

class Cat extends Animal {
    @Override
    public void makeSound() {
        System.out.println("喵喵喵");
    }
}

public class Main {
    public static void main(String[] args) {
        // 封装示例
        Person person = new Person();
        person.setName("张三");
        person.setAge(25);
        System.out.println(person.getName() + " 的年龄是 " + person.getAge());

        // 继承示例
        Student student = new Student();
        student.setName("李四");
        student.setAge(20);
        student.setStudentId("2023001");
        System.out.println(student);

        // 多态示例
        Animal animal1 = new Dog();
        Animal animal2 = new Cat();
        animal1.makeSound(); // 输出: 汪汪汪
        animal2.makeSound(); // 输出: 喵喵喵
    }
}