Java Interners

An extremely lightweight Java interners library.
Allows to add intern() method (similarly to String.intern()) to your immutable classes with customizable interners.

There is some standard interner implementations:

MapInterner - interner based on java.util.Map (java.util.HashMap in particular)
ConcurrentMapInterner - same as MapInterner but based on ConcurrentMap
ProbInterner - interner that accepts the chance to deduplicate a given value and the parent interner (which technically makes it just a deduplicator and not an interner, but anyway).

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Usage

import com.ydo4ki.interners.ConcurrentMapInterner;
import com.ydo4ki.interners.Internable;
import com.ydo4ki.interners.Interner;
import com.ydo4ki.interners.MapInterner;

class MyImmutableClass implements Internable<MyImmutableClass> {

    private final int x;
    private final long a;

    MyImmutableClass(int x, long a) {
        this.x = x;
        this.a = a;
    }

    private static final MapInterner<MyImmutableClass> interner = new ConcurrentMapInterner<>();

    @Override
    public Interner<MyImmutableClass> interner() {
        return interner;
    }

    public static MyImmutableClass create(int x, long a) {
        return new MyImmutableClass(x, a).intern(); // returns the canonical instance with x and a values
    }

    public static void dropInterner() {
        interner.clear(); // clear the table of MyImmutableClass
    }

    // it is important to define equals and hashcode so the interner maps knows which two instances are considered equal.
    @Override
    public boolean equals(Object o) {
        if (o == null || getClass() != o.getClass()) return false;

        MyImmutableClass that = (MyImmutableClass) o;
        return x == that.x && a == that.a;
    }

    @Override
    public int hashCode() {
        int result = x;
        result = 31 * result + Long.hashCode(a);
        return result;
    }
}

Installation

Maven

<dependency>
    <groupId>com.ydo4ki</groupId>
    <artifactId>Interners</artifactId>
    <version>1.0.1</version>
</dependency>

Gradle

implementation 'com.ydo4ki:Interners:1.0.1'

No build system

Go to the releases tab and download latest jar

How to build

1. Clone this repository

git clone https://github.com/Y-Sulphuris/Interners.git
cd Interners

2. Run maven build:

mvn clean package