com.trivago.triava.collections

Interface Interner<T>

Type Parameters:

T - The type to intern

All Known Implementing Classes:

HashInterner

public interface Interner<T>

Interface for interning objects, similar to String.intern() but generic and multi-instance capable. The use case for an Interner is to save memory and reduce garbage collection work. Recommended use is on deserialization of common objects from DB, Cache or REST-Interfaces.

Example: Memory and GC calculation for short strings: A locale code like "EN" can be estimated to 56 byte:

• 12 byte : object header for the String
• 4 byte: for cached int hash
• 4 byte : The reference to the char array, assuming compressed OOPS
• Sum : 24 byte (20 byte plus 4 byte padding/waste)

• 16 byte : object header for the char array
• 8 byte: 2*length for the char array
• Sum : 24 byte

Each locale code String thus takes 48 byte (24+24). If 1 Million Strings like these are shared (it could even be 1 million times the same string "EN"), 48 MB will be saved. Longer Strings have more saving potential. Often more important, the garbage collector has to visit 1 Million objects less.

Author:

cesken

Method Summary

Modifier and Type	Method and Description
T	get(T value) Returns a shared instance for the given value.

Method Detail

get

T get(T value)

Returns a shared instance for the given value. The given value is interned similar to String.intern(), if it is not found. Identity is determined in an implementation specific way, which is documented by the implementation.

Further calls with the same value will typically return the interned value, but this interface does not mandate that the same shared instance is returned under under all circumstances. The implementing class should clearly document exemptions. Typical reasons are values that are only stored for a limited lifetime, or tradeoffs during concurrent writes for the sake of speed.

Implementations must be thread-safe.

Parameters:

value - The value to intern

Returns:

The shared instance, or null for a null value