重写equals（）方法public boolean equals(Object obj)，if(obj instanceof Customer)这句代码如何理解？

Question

package equal;

public class Customer {
    
    public static void main(String[] args) {
        Customer cust1 = new Customer("Tom",21);
        Customer cust2 = new Customer("Tom",21);
        System.out.println(cust1.equals(cust2));
    }
    
    private String name;
    private int age;
    
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
    public Customer() {
        super();
    }
    public Customer(String name, int age) {
        super();
        this.name = name;
        this.age = age;
    }
    
    //重写的原则：比较两个对象的实体内容(即：name和age)是否相同，重写必须是同名同参数的。
    @Override
    public boolean equals(Object obj) {//形参是Object类型的。Object obj = cust2；Object obj = new Customer("Tom",21)
        if(this == obj) return true;
        if(obj instanceof Customer) {
        //判断obj是否为Customer类的实例。Customer会继承Object，
            Customer cust = (Customer)obj;
            if(this.age == cust.age && this.name.equals(cust.name)) return true;
            else return false;
        }else return false;
    }
    
}

是多态性的体现吗？obj instanceof Customer不是判断obj是否为Customer的实例吗，但是obj不是Object类的实例吗，怎么还是Customer的实例呢？

Answer 1

Object 是所有类的超类，所以Customer类也可以用Object 来接收，if(obj instanceof Customer) 表示这个对象类型是不是Customer类型