ArrayListのスレッドセキュリティと非セキュリティの比較デモ

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Random;

public class ThreadSafeDemo {
    public static int demo(final List list, final int testCount) throws InterruptedException {
        ThreadGroup group = new ThreadGroup(list.getClass().getName() + "@" + list.hashCode()); 
        final Random rand = new Random(); 
        
        Runnable listAppender = new Runnable() {
            public void run() {
                try {
                    Thread.sleep(rand.nextInt(2));
                } catch (InterruptedException e) {
                    return; 
                } 
                list.add("0"); 
            }
        }; 
        
        for (int i = 0; i < testCount; i++) {
            new Thread(group, listAppender, "InsertList-" + i).start(); 
        }
        
        while (group.activeCount() > 0) {
            Thread.sleep(10); 
        }
        
        return list.size(); 
    }
    public static void main(String[] args) throws InterruptedException {
        List unsafeList = new ArrayList(); 
        List safeList = Collections.synchronizedList(new ArrayList()); 
        final int N = 10000; 
        for (int i = 0; i < 10; i++) {
            unsafeList.clear(); 
            safeList.clear(); 
            int unsafeSize = demo(unsafeList, N); 
            int safeSize = demo(safeList, N); 
            System.out.println("unsafe/safe: " + unsafeSize + "/" + safeSize); 
        }
    }
}