平面元构造方法不理解

问题遇到的现象和发生背景

problem1：为什么把构造方法写在class 里面的时候下面没办法用new Circle
我把构造方法写在外面的时候就可以了呢
problem2：建类的时候为什么要在z1前面加w1 变成w1.z1呢 我单纯用z1的时候发现不行

package w1.z1;

import java.util.Scanner;


class Point{
    double x;
    double y;
    public Point(double x,double y) {
        this.x = x;
        this.y = y;
    }
    public String toString() {
        return"("+x+","+y+")";
    }
}
class Circle{
    double x;
    double y;
    double r;
    public Circle() {
        this.x = 0;
        this.y = 0;
        this.r = 0;
    }
    public Circle(double x,double y,double r) {
        this.x = x;
        this.y = y;
        this.r = r;
    }
    public Circle(Point p,double r) {
        this.x = p.x;
        this.y = p.y;
        this.r = r;
    }
    public String toString() {
        return"("+"("+x+","+y+")"+","+r+")";
    }
}
    
public  class z1 {
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        //Scanner sc = new Scanner(System.in);
        System.out.println(new Circle());
        Circle c = new Circle(1,1,3);
        System.out.println(c);
        Point p = new Point(3,4);
        System.out.println(new Circle(p,5));
        
    }



    }

1.你把point类放到z1类里面的时候，顺便把Circle类给删没了，当然没法访问了
2.跟你整个工程的包名有关系