Java 如何将数组添加到ArrayList？

我有一个int[3][3]数组，它只包含0或1个值， 如果值为1，我想在ArrayList中将该值的坐标添加为int[2]数组，但我不知道为什么它总是添加最后一个1值坐标，有什么问题

public static void main(String[] args) {

    Random random = new Random();
    int[] coordinates = new int[2];
    ArrayList<int[]> arrayList = new ArrayList<>();
    int[][] board = new int[3][3];

    for (int i = 0; i < board.length; i++) {
        for (int j = 0; j < board[i].length; j++) {
            board[i][j] = random.nextInt(2);
        }
    }

    for (int i = 0; i < board.length; i++) {
        for (int j = 0; j < board[i].length; j++) {
            System.out.print(board[i][j] + " ");
            if (board[i][j] == 1){
                coordinates[0] = i;
                coordinates[1] = j;
                arrayList.add(coordinates);

            }
        }
        System.out.println();
    }

    System.out.println("coordinates of cells that contain 1 value");

    for (int[] coordianate : arrayList) {
        for (int i = 0; i < coordianate.length; i++) {
            System.out.print(coordianate[i] + " ");
        }
        System.out.println();
    }
}

您需要为要放置在列表中的每个i，j对创建新的坐标数组。现在，您要多次放置同一数组，以记住最后一对集合

换句话说，你需要

if (board[i][j] == 1) {
    coordinates = new int[2];//add this line
    coordinates[0] = i;
    coordinates[1] = j;
    arrayList.add(coordinates);

}

您需要为要放置在列表中的每个i，j对创建新的坐标数组。现在，您要多次放置同一数组，以记住最后一对集合

换句话说，你需要

if (board[i][j] == 1) {
    coordinates = new int[2];//add this line
    coordinates[0] = i;
    coordinates[1] = j;
    arrayList.add(coordinates);

}

---

每次添加坐标对象时，都需要创建新的坐标对象：

if (board[i][j] == 1) {
  int[] coordinate = new int[2];
  coordinate[0] = i;
  coordinate[1] = j;
  arrayList.add(coordinate);
}

或更短：

if (board[i][j] == 1) {
    arrayList.add(new int[]{i, j} );
}

否则，将多次添加同一对象，并每次对其进行修改，以便只保留最后一个坐标

---

如果您养成了使用窄范围临时变量的习惯，这通常是很自然的，因为您不会在循环外部拖动状态。

每次添加坐标对象时，您都需要创建一个新的坐标对象：

if (board[i][j] == 1) {
  int[] coordinate = new int[2];
  coordinate[0] = i;
  coordinate[1] = j;
  arrayList.add(coordinate);
}

或更短：

if (board[i][j] == 1) {
    arrayList.add(new int[]{i, j} );
}

否则，将多次添加同一对象，并每次对其进行修改，以便只保留最后一个坐标

---

如果您养成了使用窄范围临时变量的习惯，这通常是很自然的，因为您不会在循环外部拖动状态。

如果要将点放入ArrayList，我建议您创建一个采用坐标的点对象。请参考下面的代码。对不起，回复太长了

import java.util.ArrayList;
import java.util.Arrays;

public class SomeClass {

    static class Point {

        int[] coordinates;

        public Point(int x, int y) {
            this.coordinates = new int[2];
            this.coordinates[0] = x;
            this.coordinates[1] = y;
        }

        public Point() {
            this(0,0);
        }

        public Point(int[] coordinates) {
            this.coordinates = coordinates;
        }
    }

    public static void main(String[] args) {
        SomeClass myClass = new SomeClass();
        Point a = new Point();
        Point b = new Point(5,5);
        Point c = new Point(new int[]{3,4});

        ArrayList<Point> arr = new ArrayList<Point>();

        // adding
        arr.add(a);
        arr.add(b);
        arr.add(c);

        // retrieve one object
        int index = 0;
        Point retrieved = arr.get(index);
        System.out.println("Retrieved coordinate: " + Arrays.toString(retrieved.coordinates));
        retrieved.coordinates[0] = 15;
        retrieved.coordinates[1] = 51;
        System.out.println("After change, retrieved coordinate: " + Arrays.toString(retrieved.coordinates));
        System.out.println("After change, accessing arraylist index: " + Arrays.toString(arr.get(index).coordinates));

        // we received a pointer to the array
        // changed values are automatically reflected in the ArrayList

    }
}

---

如果要将点放入ArrayList，我建议您创建一个获取坐标的点对象。请参考下面的代码。对不起，回复太长了

import java.util.ArrayList;
import java.util.Arrays;

public class SomeClass {

    static class Point {

        int[] coordinates;

        public Point(int x, int y) {
            this.coordinates = new int[2];
            this.coordinates[0] = x;
            this.coordinates[1] = y;
        }

        public Point() {
            this(0,0);
        }

        public Point(int[] coordinates) {
            this.coordinates = coordinates;
        }
    }

    public static void main(String[] args) {
        SomeClass myClass = new SomeClass();
        Point a = new Point();
        Point b = new Point(5,5);
        Point c = new Point(new int[]{3,4});

        ArrayList<Point> arr = new ArrayList<Point>();

        // adding
        arr.add(a);
        arr.add(b);
        arr.add(c);

        // retrieve one object
        int index = 0;
        Point retrieved = arr.get(index);
        System.out.println("Retrieved coordinate: " + Arrays.toString(retrieved.coordinates));
        retrieved.coordinates[0] = 15;
        retrieved.coordinates[1] = 51;
        System.out.println("After change, retrieved coordinate: " + Arrays.toString(retrieved.coordinates));
        System.out.println("After change, accessing arraylist index: " + Arrays.toString(arr.get(index).coordinates));

        // we received a pointer to the array
        // changed values are automatically reflected in the ArrayList

    }
}