Question

我正在尝试删除周边12为三角形的所有元素，我设置了一个if语句，用for循环检查数组列表中三角形对象的所有周长。

我的问题是，当我运行for循环时，它会删除所有三角形，其周长等于12但是最后一个，它仍将显示在输出中。

代码：

double smallestTriangle = 0.0;
double biggestCircle = 0.0;

/*for loops to get the smallest triangle(12) and largest circle(63.xx)*/

for(int i = 0; i < ShapeList.size(); i++) {
    if (ShapeList.get(i).getClass().getName() == "Triangle") {
        System.out.println(ShapeList.get(i));
        System.out.println(ShapeList.get(i).getPerimeter() + " - " + smallestTriangle);
        if (ShapeList.get(i).getPerimeter() == smallestTriangle) {
            ShapeList.remove(i);
            System.out.println("REMOVED!");
        }
    }
    if (ShapeList.get(i).getClass().getName() == "Circle") {
        if (ShapeList.get(i).getPerimeter() == biggestCircle) {
            ShapeList.remove(i);
        }
    }
}

输出：

Triangle {a=3.0 b=4.0 c=5.0} perimeter = 12.0
12.0 - 12.0
REMOVED!
Triangle {a=3.0 b=4.0 c=5.0} perimeter = 12.0
12.0 - 12.0
REMOVED!
Triangle {a=4.9 b=5.0 c=8.9} perimeter = 18.8
18.8 - 12.0
Triangle {a=3.1 b=4.1 c=5.1} perimeter = 12.299999999999999
12.299999999999999 - 12.0
Triangle {a=4.0 b=5.0 c=6.0} perimeter = 15.0
15.0 - 12.0
Triangle {a=3.1 b=4.0 c=5.0} perimeter = 12.1
12.1 - 12.0
Triangle {a=3.9 b=4.8 c=5.7} perimeter = 14.399999999999999
14.399999999999999 - 12.0
Circle {r=1.0} perimeter = 6.283185307179586
Circle {r=2.111} perimeter = 13.263804183456108
Circle {r=1.1} perimeter = 6.911503837897546
Triangle {a=3.9 b=4.0 c=5.9} perimeter = 13.8
Square {l=3.0} perimeter = 12.0
Rectangle {l=3.0 w=5.1} perimeter = 16.2
Square {l=5.0} perimeter = 20.0
Triangle {a=4.9 b=5.0 c=8.9} perimeter = 18.8
Rectangle {l=8.0 w=2.1} perimeter = 20.2
Circle {r=3.8} perimeter = 23.876104167282428
Triangle {a=3.1 b=4.1 c=5.1} perimeter = 12.299999999999999
Triangle {a=4.0 b=5.0 c=6.0} perimeter = 15.0
Rectangle {l=3.1 w=5.2} perimeter = 16.6
Circle {r=10.0} perimeter = 62.83185307179586
Triangle {a=3.1 b=4.0 c=5.0} perimeter = 12.1
Circle {r=2.0} perimeter = 12.566370614359172
Circle {r=3.0} perimeter = 18.84955592153876
Rectangle {l=3.0 w=5.2} perimeter = 16.4
Square {l=100.1} perimeter = 400.4
Square {l=100.2} perimeter = 400.8
Triangle {a=3.0 b=4.0 c=5.0} perimeter = 12.0 // <- not getting removed
Triangle {a=3.9 b=4.8 c=5.7} perimeter = 14.399999999999999

数组列表：

Triangle {a=3.0 b=4.0 c=5.0} perimeter = 12.0
Circle {r=1.0} perimeter = 6.283185307179586
Circle {r=2.111} perimeter = 13.263804183456108
Circle {r=1.1} perimeter = 6.911503837897546
Triangle {a=3.0 b=4.0 c=5.0} perimeter = 12.0
Triangle {a=3.9 b=4.0 c=5.9} perimeter = 13.8
Square {l=3.0} perimeter = 12.0
Rectangle {l=3.0 w=5.1} perimeter = 16.2
Square {l=5.0} perimeter = 20.0
Triangle {a=4.9 b=5.0 c=8.9} perimeter = 18.8
Rectangle {l=8.0 w=2.1} perimeter = 20.2
Circle {r=3.8} perimeter = 23.876104167282428
Triangle {a=3.1 b=4.1 c=5.1} perimeter = 12.299999999999999
Triangle {a=4.0 b=5.0 c=6.0} perimeter = 15.0
Rectangle {l=3.1 w=5.2} perimeter = 16.6
Circle {r=10.0} perimeter = 62.83185307179586
Triangle {a=3.1 b=4.0 c=5.0} perimeter = 12.1
Circle {r=2.0} perimeter = 12.566370614359172
Circle {r=3.0} perimeter = 18.84955592153876
Rectangle {l=3.0 w=5.2} perimeter = 16.4
Square {l=100.1} perimeter = 400.4
Square {l=100.2} perimeter = 400.8
Circle {r=10.1} perimeter = 63.46017160251382
Triangle {a=3.0 b=4.0 c=5.0} perimeter = 12.0 //this element isn't getting removed
Triangle {a=3.9 b=4.8 c=5.7} perimeter = 14.399999999999999

Answer 1

你的问题是arrayList在每个循环中减小了大小例如，如果arrayList大小为23，则下一个循环将为22，在这种情况下没有23的索引，我建议你在iterator上迭代arrayList，或者以最后一个以first结尾的索引开始一个向后循环索引

Answer 2

你还删除了一些圈子吗？

似乎正在发生的事情是，每次从列表中删除一个形状时，您都会跳过＆＃34;跳过＆＃34;下一个。从列表中删除一个元素时，将所有后续元素的索引减1。因此，如果你删除元素22，那么下一个元素的新索引是22，但你最后用一个简单的for循环来滑动它。

你能做的是：

将您的迭代更改为向后（从较高的索引到0）

for(int i = ShapeList.size() - 1; i >=0 ; i--) {...}

重新创建包含要保留的元素的新形状列表，然后丢弃旧列表

更新：我重读了您的代码，我非常肯定您必须连续删除两个实体时出现问题。您删除了最后一个三角形之前的最大圆圈，因此在增加索引时跳过它。我同意Basil Battikhi的说法，对于你的问题来说，反向循环顺序是完美的！

Answer 3

问题是在使用数组删除后，你的元素向左移动，所以你的索引i在每次删除后都会跳过1个值： 删除此列表中指定位置的元素。将任何后续元素向左移位（从索引中减去一个）。有关详细信息，请查看javadoc。您可以轻松地为每个不需要的元素位置/索引创建另一个列表，并在之后删除它们。

元素未被IF声明识别

3 个答案: