java - 面向对象的 Java 点和方法继承

Question

现在我有几个类(class):

文件1

package simplestart;

import simplegui.SimpleGUI;
public class Point {
    int x, y;
    public Point(int a, int b){
        this.x = a;
        this.y = b;
    }
    public void drawLine(Object data, SimpleGUI sg){    
        Node current = new Node(data);     
    }
    public int getX(){
        return x;
    }
    @Override
    public String toString(){
        return(x + " " + y);
    }
}

文件2

package simplestart;
import simplegui.SimpleGUI;
import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;
public class SimpleStart {
    public static void main(String[] args){
        int x, y;
        SimpleGUI sg = new SimpleGUI();
        sg.setTitle("Shape Abstraction");
        sg.centerGUIonScreen();
        LinkedList l1 = new LinkedList();
        File fl = new File("shapelist.txt");
        Scanner scan = new Scanner(fl);
        while(scan.hasNext()){
            x = scan.nextInt();
            y = scan.nextInt();
            Point p = new Point(x, y);
            l1.insertFirst(p);
        }
        l1.traverseList(l1, sg);
        l1.abstractList(l1, sg);
    }
}

文件3

package simplestart;
public class Node {
    Object data;
    Node next;

    public Node(Object data){
        this.data = data;
    }
}

文件4

package simplestart;

import simplegui.SimpleGUI;

public class LinkedList {
    Node START;
    public LinkedList(){
        START = null;
    }
    public void insertFirst(Object data){
        Node n = new Node(data);
        n.next = START;
        START = n;
    }

    public void traverseList(Object data, SimpleGUI sg){
        Node current = START;
        int x, y, ex, ey;
        while(current != null){        
            //This is where I'm trying to pull the data from Class Point
            //The error that appears is can't find symbol int x
            x = current.data.x;
            y = current.data.y;
            ex = current.next.data.x; 
            ey = current.next.data.y;
            sg.drawLine(x, y, ex, ey);
            //toString() is an override method in Class Point
            System.out.println(current.data);
            //However, this doesn't work... which I don't get cause it's also a method in Class Point like toString()
            current = current.next;   
        }
    }
    public void abstractList(Object data, SimpleGUI sg){
        Node current = START;
        Node temp = START;
        current = current.next;
        int lp, pr, rl, s;
        while(current.next != null){
            lp = current.next.data.x ­ current.data.x;
            pr = current.next.next.data.x ­ current.next.data.x;
            rl = current.next.next.data.x ­ current.data.x;
            s = lp + pr ­ rl;
            current.next.data = s;
            temp = current.next;
            current = current.next.next;
        }
    }
}

基本上，我在文件 1 中取一个点，以文件 3 中节点的形式将这些点添加到文件 2 中的链接列表中，并在文件 4 中迭代它们。但是，当 current.data 应该是每个节点时对于点，我无法访问方法“getX()”，甚至无法访问 current.data.x。我很好奇为什么会这样，但我一生都无法弄清楚。任何帮助都是非常必要的!

Answer 1

无法访问数据上的点的原因是 Node 的 data 属性是 Object 类型。

如果您想获得该属性(property)，您可以例如

• 将属性转换为Point

  ((Point)current.data).x

• 引入您自己的 Node 类，该类具有 Point 类型的属性(也可以是通用的)

正如 Andy 指出的，我还强烈建议实现您自己的节点类。这样做的优点是，您将获得语言支持，并且不需要进行转换，并且如果您的节点数据类型发生更改，您将不会遇到运行时异常 - 编译器会告诉您。