Question

我正在尝试创建一个类来计算5种不同形状的总面积和周长，但是给定形状的每个区域和周长都是由一个单独的线程计算的。到目前为止，我无法正确地同步线程，因此可以正确计算totalArea和totalPerimeter。任何建议让线程工作？如果我不用线程计算每个形状，则下面代码的totalArea和totalPerimeter应该等于该区域的610.829和周长的187.115。如果我这样做，价值会变得完全随机。

package PartB;

import PartA.Step2.*;

import java.util.*;
import java.util.concurrent.CopyOnWriteArrayList;



public class Picture implements Runnable{
    public List<Shape> picture;
    public Shape selectedShape;
    public ListIterator<Shape> e;
    double totalArea;
    double totalPerimeter;
    double a;
    double b;
    double c;
    double length;
    double width;
    double height;
    double radius;


    public Picture(double a, double b, double c, double length, double width, double height, double radius){
        this.a = a;
        this.b = b;
        this.c = c;
        this.length = length;
        this.width = width;
        this.radius = radius;
        this.height = height;
        Shape[] shapes = {new Circle(radius), new Square(length),
                new Rectangle(length, width), new Parallelogram(length, width, height),
                new Triangle(a, b, c)};
        picture = new CopyOnWriteArrayList<>(Arrays.asList(shapes));

    }

    public double getTotalArea(){return totalArea;}

    public double getTotalPerimeter(){return totalPerimeter;}


    @Override
    public void run() {

        synchronized (this) {
        totalArea += selectedShape.getArea();
        totalPerimeter += selectedShape.getPerimeter();
        System.out.println(totalArea);
        System.out.println(totalPerimeter);
    }

    }

    public static void main(String[] args){
        Picture pictures = new Picture(5, 6, 7, 8, 9, 10, 11);
        for(pictures.e = pictures.picture.listIterator(); pictures.e.hasNext();){
            pictures.selectedShape = pictures.e.next();
            new Thread(pictures).start();
        }
    }
}

形状界面：

package PartA.Step2;

public interface Shape {
    double getPerimeter();
    double getArea();
}

其中一个形状的子类：

package PartA.Step2;

public class Circle implements Shape, Cloneable {
    double radius;


    public Circle(double radius){
        this.radius = radius;
    }
    @Override
    public double getArea() {
        CalculateShape calc = (radius)->Math.PI * Math.pow(radius[0], 2);
        return calc.process(radius);

    }

    @Override
    public double getPerimeter() {
        CalculateShape calc = (radius)->2 * Math.PI * radius[0];
        return calc.process(radius);

    }



    @Override
    public String toString() {
        return "Area: " + getArea() +
                "\nPerimeter : " + getPerimeter();
    }

    @Override
    protected Object clone() throws CloneNotSupportedException {
        return super.clone();
    }

    @Override
    public boolean equals(Object obj) {
        if(obj instanceof Circle){
            if(((Circle) obj).radius == radius)
                return true;
        }
        return false;
    }
}

Answer 1

我忘了有一种方法可以让主线程等到线程不再存在。通过这样做，我能够使每个线程计算形状区域和周长而不受其他线程的干扰。 @cheiron说，同步部分毫无意义：

 public static void main(String[] args){
        Picture pictures = new Picture(5, 6, 7, 8, 9, 10, 11);
        for(pictures.e = pictures.picture.listIterator(); pictures.e.hasNext();){
            pictures.selectedShape = pictures.e.next();
            Thread thread = new Thread(pictures);
            thread.start();
            while(thread.isAlive()){
                try {
                    thread.join();
                }catch(InterruptedException e){
                    e.printStackTrace();
                }
            }
        }
    }

我现在可以获得整个图片的正确总面积和总周长。

线程未正确同步

1 个答案: