com.trivago.triava.collections

Class HashInterner<T>

java.lang.Object

com.trivago.triava.collections.HashInterner<T>

All Implemented Interfaces:

Interner<T>

public class HashInterner<T>
extends Object
implements Interner<T>

Hash based implementation of Interner. Identity is determined via Object.equals(Object) and Object.hashCode(), thus stored instances must guarantee that hashCode is consistent with equals. This implementation can return different object references in the case of two concurrent get(Object) calls

Speed: The implementation is twice as fast as Guavas Interner, and 5 times as fast as String.intern(). Measurement via bb Microbenchmark tool (ticket SRT-6053). Time in microseconds (us) for 1000 interns:

• 18us triava HashInterner
• 32us Guava Weak Interner
• 39us Guava Strong Interner
• 88us String.intern() - the 88us average had a very high deviation.

Since:

2012-08-10

Author:

cesken

Constructor Summary

Constructors

Constructor and Description
HashInterner() Creates an Interner with 100 expected elements as sizing hint for the underlying Map.
HashInterner(int expectedElements) Creates an Interner with expectedElements as sizing hint for the underlying Map.

Method Summary

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

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

HashInterner

public HashInterner()

Creates an Interner with 100 expected elements as sizing hint for the underlying Map.

HashInterner

public HashInterner(int expectedElements)

Creates an Interner with expectedElements as sizing hint for the underlying Map.

Parameters:

expectedElements - The expected number of elements

Method Detail

get

public T get(T value)

Description copied from interface: Interner

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.

Specified by:

get in interface Interner<T>

Parameters:

value - The value to intern

Returns:

The shared instance, or null for a null value

size

public int size()

Returns:

Returns the number of elements this instance has interned.

toString

public String toString()

Overrides:

toString in class Object