Java 线程，错误的计数器

Question

我运行下面的代码片段，并得到了意想不到的行为。也许它以正确的方式工作，但我需要让它以其他方式工作。详细信息如下。

import java.util.ArrayList;
import java.util.List;

public class TaskExample {

public static void main(String[] args) throws InterruptedException {
    final PositionHolder holder = new PositionHolder();
    final List<Integer> data = new ArrayList<Integer>();
    List<Thread> threads = new ArrayList<Thread>();
    for (int i = 0; i < 20; i++) {
        holder.setPosition(i);
        Thread t = new Thread() {

            @Override
            public void run() {
                data.add(holder.getPosition());
            }
        };

        t.start();
        threads.add(t);
    }

    for (Thread thread : threads) {            
            thread.join();
        }

    for(int i : data){
        System.out.println(i);
    }
}
}

class PositionHolder {

    int position = 0;

    public void setPosition(int position) {
        this.position = position;
    }

    public int getPosition() {
        return this.position;
    }
}

我得到了结果:

10 12 9 8 6 6 5 4 2 1 16 16 18 19 19 19 19 19 19 19

为什么？我想要得到:

1 2 3 4 ...... 20

是否有任何选项可以改进此代码段？

Answer 1

试试这个代码;)

import java.util.ArrayList;
import java.util.List;

public class ogr
{

    public static void main(String[] args) throws InterruptedException {
        final PositionHolder holder = new PositionHolder();
        final List<Integer> data = new ArrayList<Integer>();
        for (int i = 0; i < 20; i++) {
            holder.setPosition(i);
            Thread t = new Thread() {

                @Override
                public void run() {
                    data.add(holder.getPosition());
                }
            };

            t.start();
            t.join();
        }

        for (int i : data) {
            System.out.println(i);
        }
    }
}

class PositionHolder
{

    int position = 0;

    public void setPosition(int position) {
        this.position = position;
    }

    public int getPosition() {
        return this.position;
    }
}