Java泛型数组，Java泛型不指定类型参数

Question

public class generics {
    public static void main(String[] args) {
        Student<String> s1 = new Student<>("jack", "优秀");
        Student<Double> s2 = new Student<>("Tom", 95.0);
        Student<Character> s3 = new Student<>("Bob", 'A');

        Student[] students = new Student[3];
        students[0] = s1;
        students[1] = s2;
        students[2] = s3;
    }
}

class Student<T> {
    private String name;
    private T score;

    public Student(String name, T score) {
        this.name = name;
        this.score = score;
    }
}

为什么students数组可以存不同的类型呢？students是被声明成Student类型的数组了吗，这是多态吗，Student<String>、Student<Double>、Student<Character> 都是Student的子类？

如果代码写成：

Student<Object>[] students = new Student[3];
        students[0] = s1;
        students[1] = s2;
        students[2] = s3;

就直接报错了，包括下面这句代码：

Student<String> s1 = new Student<>("jack", "优秀");
Student s = s1;//不会报错
Student<Object> s = s1;//报错

不写类型不是默认Object类型吗，为什么两句话一个报错一个不报错呢。

Answer 1

这个就是java的语法检查，不允许泛型转换，即使你用的是父类。