提取包围框内的坐标文件

Question

我正在扫描一个CSV文件，看看哪些值适合在给定的框内。CSV文件具有X和Y坐标，函数的参数是框的周长(即顶部、底部、左侧、右侧)。我不想使用任何外部库；其部分目的是学习如何手动加速代码。

我对Java相当陌生，所以任何输入都是有帮助的。如果可能的话，我试着把这个降低到100毫秒，但是现在它大约需要1000毫秒。

Scanner dataStream = new Scanner(fileMain);
while (dataStream.hasNext()){
    String data = dataStream.next();
    String[] values = data.split(",", 3);
    if(Double.parseDouble(values[0]) > lowX && Double.parseDouble(values[0]) < highX){ 
            if(Double.parseDouble(values[1]) < highY && Double.parseDouble(values[1]) > lowY){
                System.out.println(data);

    }

dataStream.close();

数据的格式如下：

90.92, 102.3
40.28, 82.32
13.02, 80
72, 104.82

Answer 1

首先，请注意，您始终可以使用Point2D.Double来表示平面上的点。

接下来，我将您的程序分成两种方法:第一种用于修剪不在指定边界框内的点，第二种用于从标准输入中读取这些点，并将它们放入第一种。

对于编码约定，在if语句之前我将有一个空行。另外，您应该用一个空格包围if语句的条件。所以，而不是

String[] values = data.split(",", 3);
if(Double.parseDouble(values[0])){ ...

你应该写

String[] values = data.split(",", 3);

if (Double.parseDouble(values[0])) { ...

总之，我有这样的想法：

import java.awt.geom.Point2D;
import java.util.ArrayList;
import java.util.List;
import java.util.Objects;
import java.util.Scanner;

public class CoordinateUtilities {

    public static List<Point2D.Double> 
        getPointsWithinBoundingBox(final List<Point2D.Double> pointList,
                                   final double lowX,
                                   final double highX,
                                   final double lowY,
                                   final double highY) {
        Objects.requireNonNull(pointList, "The list of points is null.");
        checkXBounds(lowX, highX);
        checkYBounds(lowY, highY);
        final List<Point2D.Double> ret = new ArrayList<>(pointList.size());

        for (final Point2D.Double point : pointList) {
            final double x = point.x;
            final double y = point.y;

            if (lowX <= x && x <= highX && lowY <= y && y <= highY) {
                ret.add(point);
            }
        }

        return ret;
    }

    public static void main(final String... args) {
        final Scanner scanner = new Scanner(System.in);
        final double lowX  = 50.0; 
        final double highX = 100.0;
        final double lowY  = 30.0;
        final double highY = 60.0;

        final List<Point2D.Double> allPoints = new ArrayList<>();

        while (scanner.hasNextLine()) {
            final String line = scanner.nextLine();

            if (line.trim().equals("quit")) {
                break;
            }

            final Point2D.Double point = parsePoint(line);

            if (point != null) {
                allPoints.add(point);
            }
        }

        final List<Point2D.Double> boundedPoints = 
                getPointsWithinBoundingBox(allPoints, lowX, highX, lowY, highY);

        boundedPoints.forEach(System.out::println);
    }

    private static Point2D.Double parsePoint(final String line) {
        final String[] tokens = line.trim().split("\\s*,\\s*");

        if (tokens.length < 2) {
            return null;
        }

        try {
            final double x = Double.parseDouble(tokens[0]);
            final double y = Double.parseDouble(tokens[1]);
            return new Point2D.Double(x, y);
        } catch (final NumberFormatException ex) {
            return null;
        }
    }

    private static void checkXBounds(final double lowX, final double highX) {
        if (Double.isNaN(lowX)) {
            throw new IllegalArgumentException(
                    "The lower bound of the x-coordinate is NaN.");
        }

        if (Double.isNaN(highX)) {
            throw new IllegalArgumentException(
                    "The upper bound of the x-coordinate is NaN.");
        }

        if (lowX > highX) {
            throw new IllegalArgumentException(
                    "The lower bound of the x-coordinate (" + lowX + "is " +
                    "larger than the upper bound of the x-coordinate (" +
                    highX + ").");
        }
    }

    private static void checkYBounds(final double lowY, final double highY) {
        if (Double.isNaN(lowY)) {
            throw new IllegalArgumentException(
                    "The lower bound of the y-coordinate is NaN.");
        }

        if (Double.isNaN(highY)) {
            throw new IllegalArgumentException(
                    "The upper bound of the y-coordinate is NaN.");
        }

        if (lowY > highY) {
            throw new IllegalArgumentException(
                    "The lower bound of the y-coordinate (" + lowY + "is " +
                    "larger than the upper bound of the y-coordinate (" +
                    highY + ").");
        }
    }
}

希望这能帮上忙。