List cannot be resolved to a type，不知道咋回事

出现了两个错误，都是啥 cannot be resolved to a type，这是咋了，我用的vs code

import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;

public class Three {
    public static void main(String[] args) {
        List list=new ArrayList();      //List cannot be resolved to a type
        list.add();
    }
}
class Student{
    private String name;
    private int age;
    pulbic Student(String name,int age){          //pulbic cannot be resolved to a type
        this.name=name;
        this.age=age;
    }
}

import java.util.List;