EnumMap vs HashMap
- EnumMap is a specialized Map for enum keys and is very fast
- HashMap is a general-purpose Map for any object keys
Core Difference
| Point | EnumMap | HashMap |
|---|---|---|
| Key type | Enum only | Any object |
| Internal structure | Array-based | Hash table |
| Performance | Faster | Slower |
| Memory usage | Less | More |
| Allows null key | ❌ No | ✅ One |
| Allows null values | ✅ Yes | ✅ Yes |
| Ordering | Natural enum order | No order guaranteed |
| Thread-safe | ❌ No | ❌ No |
EnumMap
An EnumMap is a Map implementation designed only for enum keys.
Characteristics
- Uses array internally → very fast
- Maintains natural order of enum constants
- More memory efficient
- Does not allow null keys
When to use
- Keys are enums
- High performance is required
- Predictable ordering is useful
“EnumMap is optimized for enum keys and is faster than HashMap.”
HashMap
A HashMap is a general-purpose Map implementation.
Characteristics
- Works with any object as key
- Uses hashing
- Slightly slower than EnumMap
- Allows one null key
When to use
- Keys are not enums
- General-purpose use cases
- Flexibility is needed
“HashMap is used when keys are not restricted to enums.”
EnumMap is a specialized, high-performance map for enum keys, whereas HashMap is a general-purpose map for any object keys.