public class Demo{
  public static void main(String[] args) {
    Dog obj = new Dog();
    obj.move();
  }
}
class Animal{
  private String desc = "Animals are human's good friends";
  // 必须要声明一个 getter 方法
  public String getDesc() { return desc; }
  public void move(){
    System.out.println("Animals can move");
  }
}
class Dog extends Animal{
  public void move(){
    super.move(); // 调用父类的方法
    System.out.println("Dogs can walk and run");
    // 通过 getter 方法调用父类隐藏变量
    System.out.println("Please remember: " + super.getDesc());
  }
}

Animals can move
Dogs can walk and run
Please remember: Animals are human's good friends

public class Demo{
  public static void main(String[] args) {
    Dog obj = new Dog("花花", 3);
    obj.say();
  }
}
class Animal{
  String name;
  public Animal(String name){
    this.name = name;
  }
}
class Dog extends Animal{
  int age;
  public Dog(String name, int age){
    super(name);
    this.age = age;
  }
  public void say(){
    System.out.println("我是一只可爱的小狗，我的名字叫" + name + "，我" + age + "岁了");
  }
}

public final class Demo{
  public static void main(String[] args) {
    // 引用 People 类的实例
    People obj = new People();
    if(obj instanceof Object){
      System.out.println("我是一个对象");
    }
    if(obj instanceof People){
      System.out.println("我是人类");
    }
    if(obj instanceof Teacher){
      System.out.println("我是一名教师");
    }
    if(obj instanceof President){
      System.out.println("我是校长");
    }
    System.out.println("-----------"); // 分界线
    
    // 引用 Teacher 类的实例
    obj = new Teacher();
    if(obj instanceof Object){
      System.out.println("我是一个对象");
    }
    if(obj instanceof People){
      System.out.println("我是人类");
    }
    if(obj instanceof Teacher){
      System.out.println("我是一名教师");
    }
    if(obj instanceof President){
      System.out.println("我是校长");
    }
  }
}
class People{ }
class Teacher extends People{ }
class President extends Teacher{ }

我是一个对象
我是人类
-----------
我是一个对象
我是人类
我是一名教师