当元素具有不同类型时，object 数组的行为如何

Question

,,,

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class Try {
    public static void main(String[] args) {
        String  [] a = new String [5];
        a[0]="0";
        a[1]="1";
        List<List<String>> list = new ArrayList<>();
        list.add(Arrays.asList(a));
        for(List l : list)
        {
            System.out.println(l.get(0));
        }

        Object [] s = new Object[5];
        Object  [] d = new Object[10];

        d[0]=10;
        d[1]=10;
        d[2]="me";
        d[3]=new Integer(3);
        d[4]=new person();
        d[5]= 'x';
        for(Object i : d)
        {
            System.out.println(i);

        }
        System.out.println(new person().toString());

    }
    static class person {
        String name = "my name";
        int age = 50;

        public person()
        {
            name ="new name";
        }
        @Override
        public String  toString()
        {
            return name + "\n" + age;
        }
    }
}

,,,

i was expecting that when you create an array of objects and print it with casting it will print out hashcode.. but this code above printed the value as if it would if it was casted any idea if this a new java feature??

Answer 1

System.out.println(x) will call x 's toString() method. Unless overridden, that method will print out the object's location in memory. You have overridden it. This is because subclass methods are "retained" even if assigned to a superclass.

class Foo {
    public int run() {
        return 1;
    }
}

class Baz extends Foo {
    @Override
    public int run() {
        return 2;
    }
}

...

Foo f = new Baz();
f.run(); // >>> 2