gistfile1.java

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.CopyOnWriteArrayList;

public class Hoge {
	
	public static void main(String[] args) {
//		final List<String> list = new ArrayList<String>();
		final List<String> list = new CopyOnWriteArrayList<String>();
		list.add("a");
		list.add("b");
		list.add("c");
		
		new Thread(new Runnable() {
			@Override
			public void run() {
				while (true) {
					for (String s : list) {
						System.out.println(s);
					}
				}
			}
		}).start();
		
		new Thread(new Runnable() {
			@Override
			public void run() {
				while(true) {
					list.add("d");
					try {
						Thread.sleep(1000);
					} catch (InterruptedException e) {
						e.printStackTrace();
					}
				}
			}
		}).start();
	}

}