爪哇 - 从一个ArrayList从另一个类阅读 [英] Java - Reading from an ArrayList from another class

问题描述

我们还没有覆盖的ArrayList只是数组和二维数组。我需要做的是能够从另一个类的ArrayList阅读。的主要目的是从他们在一个读循环，并使用在其中存储的值来显示的项目。不过，我已经这个快速程序来对其进行测试，并保持收到此错误

We've not covered ArrayLists only Arrays and 2D arrays. What I need to do is be able to read from an ArrayList from another class. The main aim is to read from them in a for loop and use the values stored in them to display items. However, I have made this quick program to test it out and keep getting this error

java.lang.IndexOutOfBoundsException: Index: 0, Size: 0
    at java.util.ArrayList.rangeCheck(ArrayList.java:604)
    at java.util.ArrayList.get(ArrayList.java:382)
    at Main.Main(Main.java:14)

下面是我的code

import java.util.ArrayList;

public class Main
{
    public static void Main()
    {
        System.out.println("Test");
        ArrayList <Objects> xcoords = new ArrayList<Objects>();

        for( int x = 1 ; x < xcoords.size() ; x++ )
        {
            System.out.println(xcoords.get(x));
        }
    }
}

和则该类所在的ArrayList是

And then the class where the ArrayList is

import java.util.ArrayList;

public class Objects
{
    public void xco()
    {
        ArrayList xcoords = new ArrayList();
        //X coords
        //Destroyable
        xcoords.add(5);
        xcoords.add(25);
        xcoords.add(5);
        xcoords.add(5);
        xcoords.add(25);
        xcoords.add(5);
        //Static Walls
        xcoords.add(600);
        xcoords.add(400);
        xcoords.add(600);
    }
}

如果有人能在正确的方向指向我会这么值钱。我试着调试不过，我可以得到什么帮助。

If someone can point me in the correct direction it would be so valuable. I've tried to debug however I can get anything helpful.

先谢谢了。

推荐答案

严格地说，异常是由于一个的ArrayList 0元素的索引位置1。请注意，你开始你循环变量 X 。但是，考虑这一行：

Strictly speaking, the exception is due to indexing location 1 of an ArrayList with 0 elements. Notice where you start you for loop index variable x. But consider this line:

ArrayList <Objects> xcoords = new ArrayList<Objects>();

xcoords 指向一个新的空的ArrayList ，而不是你在课堂上的对象创建的。要获得的是的的ArrayList ，改变方法 XCO 像

xcoords points to a new, empty ArrayList, not the one you created in class Objects. To get that ArrayList, change the method xco like

public ArrayList<Integer> xco() { // make sure to parameterize the ArrayList
    ArrayList<Integer> xcoords = new ArrayList<Integer>();

    // .. add all the elements ..

    return xcoords;
}

那么，在你的主法

public static void main(String [] args) { // add correct arguments

    //..
    ArrayList <Integer> xcoords = (new Objects()).xco();

    for( int x = 0 ; x < xcoords.size() ; x++ ) { // start from index 0
        System.out.println(xcoords.get(x));
    }
}

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