在数组列表的数组列表中删除

Question

public Point{
int x, y;

public Point(int x, int y){
    int x = x;
    int y = y;
}
}

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

// add points by using points.add() then use this loop 
ArrayList<ArrayList<Point>> A = new ArrayList<>();
    for (int i = 0; i < 3; i++) {
            A.add(points);

        }

我有一个arraylist的arraylist，每个arraylist都有相同的点，例如，当您打印时，这是输出

ArrayList<ArrayList<Point>> A = [[(0,10), (20,3), (2,5), (2,8)], [(0,10), (20,3), (2,5), (2,8)], [(0,10), (20,3), (2,5), (2,8)]]

在打印之前，我要删除其x值不等于数组列表索引的所有点

A.get(0) = [(0,10)]
A.get(1) = []
A.get(2) = [(2,5),(2,8)]

所以输出应该是

[[(0,10)], [], [(2,5), (2,8)]]

我尝试使用remove方法和for循环以及其他方法，但都不起作用。

for(int i = 0; i < list.size();i++){
            if(list.get(i).x != 0){
                list.remove(i--);
            }
        }

有人能帮忙吗？

Answer 1

import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;

public class teste {

    public static void main(String[] args) {

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

        points.add(new Point(0, 10));
        points.add(new Point(9, 10));
        points.add(new Point(20, 3));


        System.out.println(points);
        //solution 1
        List<Point> list = points.stream().filter(o -> !o.equals(9, 10)).collect(Collectors.toList());
        System.out.println(list);
        
        //solution 2
        List<Point> list2 = new ArrayList<>();
        points.stream().forEach(o -> {
            if (o.equals(9, 10)) {
                list2.add(null);
            } else {
                list2.add(o);
            }
        });

        System.out.println(list2);
    }



    public static class Point {
        int x, y;

        public Point(int x, int y) {
            this.x = x;
            this.y = y;
        }

        public String toString() {
            return "(" + x + ", " + y + ")";
        }

        public boolean equals(int x, int y) {
            return this.x == x && this.y == y;
        }

    }

}


[(0, 10), (9, 10), (20, 3)]
[(0, 10), (20, 3)]
[(0, 10), null, (20, 3)]

Answer 2

您可能正在寻找以下内容：

int index = 0;
for (ArrayList<Point> list : A) {
     list.removeIf(point -> point.x != index);
     index++;
}

索引变量也可以删除，但我不想过分简化代码，以保持清晰。