In Java programming, both Array and ArrayList are used to store multiple elements. However, they work differently in terms of flexibility, performance, and usage.
Understanding the difference between Array and ArrayList is very important for students, freshers, and developers because this question is frequently asked in Java interviews.
✅ What is an Array?
An Array is a fixed-size data structure used to store elements of the same data type.
Example:
int[] numbers = new int[5];
numbers[0] = 10;
numbers[1] = 20;
Key Features:
- Fixed size (cannot grow or shrink)
- Stores primitive data types directly
- Faster performance
- Part of core Java language
✅ What is an ArrayList?
An ArrayList is a dynamic data structure available in the Java Collections Framework that can grow or shrink automatically.
Example:
import java.util.ArrayList;
ArrayList<Integer> list = new ArrayList<>();
list.add(10);
list.add(20);
Key Features:
- Dynamic size (resizable)
- Stores objects only (uses wrapper classes)
- Provides many built-in methods
- Part of
java.utilpackage
📊 Difference Between Array and ArrayList
| Feature | Array | ArrayList |
|---|---|---|
| Size | Fixed | Dynamic |
| Performance | Faster | Slightly slower |
| Data Types | Primitive + Objects | Objects only |
| Memory | Less overhead | More memory usage |
| Built-in Methods | Limited | Many methods available |
| Package | Core Java | java.util package |
| Resizing | Manual | Automatic |
✅ When to Use Array?
Use Arrays when:
- Size is known in advance
- Performance is critical
- Working with primitive data types
✅ When to Use ArrayList?
Use ArrayList when:
- Size changes frequently
- Need built-in utility methods
- Working with dynamic data
🎯 Interview Tip
A common interview follow-up question is:
👉 Why ArrayList cannot store primitive data types?
Because ArrayList works with objects, Java uses Wrapper Classes like Integer, Double, and Character.
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