java iterator Fail-Safe vs Fail-Fast

IteratorFailFastAndFailSafe.java

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Iterator;
import java.util.concurrent.ConcurrentHashMap;

public class IteratorFailFastAndFailSafe {

	public static void funcFailFast() {

		ArrayList<Integer> numbers = new ArrayList<>(Arrays.asList(1, 2, 3, 4));
		Iterator<Integer> iterator = numbers.iterator();

		while (iterator.hasNext()) {
			Integer number = iterator.next();
			numbers.add(50);
			System.out.println(number);
		}
	}

	public static void funcFailSafe() {

		ConcurrentHashMap<String, Integer> map = new ConcurrentHashMap<>();
		map.put("First", 10);
		map.put("Second", 20);
		map.put("Third", 30);
		map.put("Fourth", 40);
		Iterator<String> iterator = map.keySet().iterator();

		while (iterator.hasNext()) {
			String key = iterator.next();
			map.put(key, 50);
		}
	}
	
	public static void main(String[] args) {

		funcFailFast();
		funcFailSafe();

	}

}