Some iterator basics and how concurrent modification errors happen

CISC-275-Iterators.java

import java.util.*;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;

class Main {
	public static void main(String[] args) {
		System.out.println("Hello world!");

		Collection<Dog> doggos = new ArrayList<>();

		doggos.add(new Dog("Fido"));
		doggos.add(new Dog("Spot"));
		doggos.add(new Dog("Lucy"));

		System.out.println(doggos);

		for (Dog d : doggos) {
			if (d.name.equals("Spot")) {
				System.out.println(d.toString());
			}
		}

		Iterator<Dog> dogIterator = doggos.iterator();
		while (dogIterator.hasNext()) {
			if (dogIterator.next().name.equals("Spot")) {
				//doggos.add(new Dog("Spotty Doggo")); /// ConcurrentModificationException
				//dogIterator.add(new Dog("Spotty Doggo")); /// Cannot find symbol compiler error
				//doggos.remove(dogIterator.next()); // ConcurrentModificationException
				dogIterator.remove(); // Spot went off to the big farmhouse in the sky.
			}
		}

		System.out.println(doggos);
	}

}

class Dog {
	String name;

	Dog(String dogName) {
		name = dogName;
	}

	@Override
	public String toString() {
		return ("Am dog named " + name);
	}
}

class C {
	public static void main(String[] args) {
		Set<String> set = new HashSet<String>();
		for (String arguments : args) /// For every argument given
			if (!set.add(arguments)) /// If the set does not already have a copy of a given argument, add it to the list. It it's already in the list, continue to...
				System.out.println("Already in the set: " + arguments); /// ...print it on the next line
		System.out.println(set.size() + " in set: " + set); /// Then print out the set
	}
}