An Array and an ArrayList in Java—they might sound similar, but they behave quite differently under the hood!
🧾 Key Differences Between Array and ArrayList
| Feature | Array | ArrayList |
|---|---|---|
| Size | Fixed when created | Dynamically resizable |
| Syntax | int[] arr = new int[5]; | ArrayList list = new ArrayList<>(); |
| Type Support | Can hold primitives (int, char, etc.) | Only objects (Integer, String, etc.) |
| Memory Efficiency | More memory-efficient (less overhead) | Slightly more memory usage (due to internal structure) |
| Performance | Faster in basic operations | Slightly slower due to dynamic resizing |
| Methods | No built-in methods beyond index access | Has methods like add(), remove(), contains() |
| Length Access | Use .length | Use .size() |
| Multidimensional? | Yes (int[][]) | Indirectly with ArrayList> |
| Thread Safety | Not synchronized | Not synchronized (but use Collections.synchronizedList() for thread safety) |
🛠Quick Code Comparison
// Array
int[] numbers = new int[3];
numbers[0] = 10;
// ArrayList
ArrayList list = new ArrayList<>();
list.add(10);
🧠Which One Should You Use?
- Use Array when:
You know the size in advance, and performance is critical. - Use ArrayList when:
You want dynamic sizing, easy insertion/removal, and rich built-in methods.
