列表中的对象具有相同的值-最后添加的元素的值相同 [英] Objects in List have the same value - that of the last element added

问题描述

我对JAVA有点陌生，并且遇到了很大的问题.当我将元素添加到List<int[]>时，结果将是一个具有相同值的充满列表. 为什么JAVA会这样工作?

I'm a bit new to JAVA, and having a big problem. While I'm adding elements to a List<int[]> the result will be a List full of with the same value. Why JAVA is working like this?

这是代码:

// Global variables
private static int rows = 20;
private static int columns = 30;
private static String[][] labirinth = new String[rows][columns];
private static List<int[]> walls = new ArrayList<int[]>();

// Local variables inside a function
int[] wall = new int[2];
if(row - 1 <= rows && labirinth[row-1][column] == "*")
{
    wall[0] = row-1;
    wall[1] = column;
    walls.add(wall);
}
if(row + 1 <= rows && labirinth[row+1][column] == "*")
{
    wall[0] = row+1;
    wall[1] = column;
    walls.add(wall);
}
if(column - 1 <= columns && labirinth[row][column-1] == "*")
{
    wall[0] = row;
    wall[1] = column-1;
    walls.add(wall);
}
if(column + 1 <= columns && labirinth[row][column+1] == "*")
{
    wall[0] = row;
    wall[1] = column+1;
    walls.add(wall);
}

最后，walls变量将多次保存wall的最后结果.

At the end the walls variable will hold the last result of wall at multiple times.

感谢您的帮助！

推荐答案

您始终更改同一对象:

int[] wall = new int[2];

但是每次在将新值设置到墙并将其添加到列表之前，您应该:

but each time before you set the new values to the wall and add it to the list you should:

wall = new int[2];

如果不这样做，则每次都将更改相同的墙坐标，最后只剩下一面墙，墙将具有您最后设置的坐标.

If you do not, you will just change the same wall coordinates every time and end up with just one wall which will have the coordinates that you set last.

// Local variables inside a function
int[] wall = null;
if(row - 1 <= rows && labirinth[row-1][column] == "*")
{
    wall =  new int[2];
    wall[0] = row-1;
    wall[1] = column;
    walls.add(wall);
}
if(row + 1 <= rows && labirinth[row+1][column] == "*")
{
    wall = new int[2];
    wall[0] = row+1;
    wall[1] = column;
    walls.add(wall);
}
...

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