col.java

final List<String> baseList = new ArrayList<>();
final List<String> unmodifiableList = Collections.unmodifiableList(baseList);

Executors.newSingleThreadExecutor().execute(() -> {
    while(true) {
        baseList.add(UUID.randomUUID().toString());
        try {
            Thread.sleep(10);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
});

try {
    Thread.sleep(100);
} catch (InterruptedException e) {
    e.printStackTrace();
}

for(String s : unmodifiableList) {
    System.out.println("Val: " + s);
    try {
        Thread.sleep(5);
    } catch (InterruptedException e) {
        e.printStackTrace();
    }
}