Equalizer

A small library to greatly simplify the implementation of equals() and hashCode() in Java classes (and Kotlin classes, if data classes are not enough). Java 8 or newer is required though.

Why Equalizer

• Fluent, highly readable API for EqualsBuilder, HashCodeBuilder and EqualsAndHashCodeBuilder.
• Garbage-free implementations of equals() and hashCode(): If used correctly, Equalizer does not generate any garbage like Iterators or boxed primitives.
• Configure one static instance of Equals and HashCode or EqualsAndHashCode and reuse it across all instances to minimize garbage.
• Use Java 8 lambdas to define which attributes should be compared and hashed.
• Easily honour the contracts between equals() and hashCode() without a lot of boilerplate code.
• No dependencies to other libraries

Examples

Using Equalizer is very easy.

Configure one EqualsAndHashCode to use it in both equals() and hashCode() to make sure that the contracts between the two methods are always honoured.

package org.mycompany;

import ch.leadrian.equalizer.Equalizer;
import ch.leadrian.equalizer.EqualsAndHashCode;

public class Person {

    private static final EqualsAndHashCode<Person> EQUALS_AND_HASH_CODE =
            Equalizer.equalsAndHashCodeBuilder(Person.class)
                    .compareAndHashPrimitive(Person::getAge)
                    .compare(Person::getName)
                    .build();

    private final int age;
    private final String name;

    public Person(int age, String name) {
        this.age = age;
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public String getName() {
        return name;
    }

    @Override
    public int hashCode() {
        return EQUALS_AND_HASH_CODE.hashCode(this);
    }

    @Override
    public boolean equals(Object obj) {
        return EQUALS_AND_HASH_CODE.equals(this, obj);
    }
}

Or configure Equals and HashCode separately:

package org.mycompany;

import ch.leadrian.equalizer.Equalizer;
import ch.leadrian.equalizer.Equals;
import ch.leadrian.equalizer.HashCode;

public class Person {

    private static final Equals<Person> EQUALS = 
            Equalizer.equalsBuilder(Person.class)
                    .comparePrimitive(Person::getAge)
                    .compare(Person::getName)
                    .build();

    private static final HashCode<Person> HASH_CODE = 
            Equalizer.hashCodeBuilder()
                    .hashPrimitive(Person::getAge)
                    .build();

    private final int age;
    private final String name;

    public Person(int age, String name) {
        this.age = age;
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public String getName() {
        return name;
    }

    @Override
    public int hashCode() {
        return HASH_CODE.hashCode(this);
    }

    @Override
    public boolean equals(Object obj) {
        return EQUALS.equals(this, obj);
    }
}

You may also use it in Kotlin, in case data classes are not an option or you are required to use an array in equals or hashCode:

package org.mycompany

import ch.leadrian.equalizer.equals
import ch.leadrian.equalizer.hashCode
import ch.leadrian.equalizer.invoke

class Book(
        val title: String,
        val numberOfPages: Int,
        val authors: Array<String>
) {

    companion object {

        private val EQUALS = equals<Book> {
            compare { title }
            compareInt { numberOfPages }
            compareDeep { authors }
        }

        private val HASH_CODE = hashCode<Book> {
            hash { title }
            hashInt { numberOfPages }
            hashDeep { authors }
        }

    }

    override fun equals(other: Any?): Boolean = EQUALS(this, other)

    override fun hashCode(): Int = HASH_CODE(this)

}

Downloads

Core

For Maven:

<dependency>
  <groupId>ch.leadrian.equalizer</groupId>
  <artifactId>equalizer-core</artifactId>
  <version>1.2.1</version>
</dependency>

For Gradle (Groovy DSL):

implementation 'ch.leadrian.equalizer:equalizer-core:1.2.1'

For Gradle (Kotlin DSL):

implementation("ch.leadrian.equalizer:equalizer-core:1.2.1")

Kotlin

For Maven:

<dependency>
  <groupId>ch.leadrian.equalizer</groupId>
  <artifactId>equalizer-kotlin</artifactId>
  <version>1.2.1</version>
</dependency>

For Gradle (Groovy DSL):

implementation 'ch.leadrian.equalizer:equalizer-kotlin:1.2.1'

For Gradle (Kotlin DSL):

implementation("ch.leadrian.equalizer:equalizer-kotlin:1.2.1")