不规则多边形程序 [英] Irregular Polygon Program

问题描述

以下是我需要帮助的作业：

1.实现一个包含Point2D.Double对象数组列表的IrregularPolygon类。


2. Point2D.Double类定义以double精度指定的点，表示（x，y）坐标空间中的位置。例如，Point2D.Double（2.5,3.1）构造并初始化坐标（2.5,3.1）处的点。


3.使用以下声明作为实验室工作的起点。

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解决方案

@ slapsh0t11


It会更直接地说：

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程序确实编译了，但是我的代码中以及非测试文件中的toAdd方法中显示的行似乎正在发生。



以下是我一直收到的错误消息：


输入X坐标：3

输入Y坐标：4

线程main中的异常java.lang.NullPointerException

at IrregularPolygon.toAdd（IrregularPolygon.java:28）

at IrregularPolygonTester.main（IrregularPolygonTester .java：19）

OK。


所以你有一个NullPointerException：这意味着当它不应该是某个东西时是空的。如果你取消引用一个null的变量（例如，尝试并调用一个null的方法），或者如果一个数组变量为null并且你试图访问它的一个元素，你就得到这些。


此异常发生在IrregularPolygon.java的第28行

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Here is my assignment that I need help with:
1. Implement a class IrregularPolygon that contains an array list of Point2D.Double objects.

2. The Point2D.Double class defines a point specified in double precision representing a location in (x, y) coordinate space. For example, Point2D.Double(2.5, 3.1) constructs and initializes a point at coordinates (2.5, 3.1).

3. Use the following declarations as a starting point for your lab work.

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解决方案

@slapsh0t11
It would be more straight forward to say:

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The program does compile, but something seems to be going on with the line I indicated in my code as well as in the toAdd method in the non-tester file.


Here is the error message I keep receiving:

Enter X-Coordinate: 3
Enter Y-Coordinate: 4
Exception in thread "main" java.lang.NullPointerException
at IrregularPolygon.toAdd(IrregularPolygon.java:28)
at IrregularPolygonTester.main(IrregularPolygonTester .java:19)

OK.

So you have a "NullPointerException": that means that something is null when it shouldn''t be. You get these if you dereference a variable which is null (eg try and invoke a method on something that is null), or if an array variable is null and you try and access one of its elements.

This exception occurs at line 28 of IrregularPolygon.java

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