What are the differences between ArrayList and Vector?

When speed is your need: ArrayList vs. Vector performance

ArrayList outruns Vector because it says no to synchronization. See, synchronization in java is like carrying luggage while running, it slows you down (think of synchronized methods as suitcases). If your program runs in a single-threaded environment, ArrayList is the Usain Bolt – the fastest option. If multiple threads are involved, use Vector or manage ArrayList synchronization yourself (Like checking in those suitcases).

Memory matters: How ArrayList and Vector grow

Both ArrayList and Vector increase in size, but they do it differently. The ArrayList increases by 50% of its current size, while the Vector says 'Go Big Or Go Home' – it doubles its size. That's why Vector could end up with a lot of empty spaces (much like a poorly attended rock concert), using more memory.

Goodbye big guy: The legacy of Vector

Vector is part of the old guard. It lacks the flexibility and ease of use offered by ArrayList and is typically not used in new code. So Vector is like a vintage car – will get you there but lacks the sophistication of modern models. If you need synchronization for ArrayList, check out Collections.synchronizedList, it retains ArrayList advantages and acts like an upgrade.

Customizing control using external synchronization

This is where you can enjoy some freedom. You can use Collections.synchronizedList or CopyOnWriteArrayList with ArrayList for a thread-safe list implementation. This lets you design granularity levels according to your application's needs.

Nomenclature: How ArrayList wins on friendliness

ArrayList functions have fancier and modern names - they're the cool kids. Vector, on the other hand, can't let go of the old ways. Coding with ArrayList is more pleasant; like playing a grand piano, whereas Vector feels more like using a typewriter.

Not all roses: Compound actions and Thread safety

Just because Vector functions are synchronized doesn't mean it's always thread safe. It’s like putting a ferocious lion (your data) in a cage (synchronization) but forgetting about the gaps. With operations like "iterate" or "check then act", Vector or indeed even ArrayList isn't safe. Here you need extra synchronization. It’s like having a second cage around the first one.

One size doesn't fit all: Best usage scenario

Choose ArrayList when you want performance, provided the access is non-critical and synchronization is managed. If dealing with a legacy system or you need thread safety without going into the complexities of synchronization, Vector is your friend.

When Vector gets its day

Vector, despite being the older bloke, can be useful. When a simple, multi-threaded solution is needed and there is no time for synchronizedList, Vector can come in and save the day.