Apache Commons Lang: Builders Example

While it's been around for a while (version 1.0 was released in 2002), I recently discovered Apache Commons Lang and its various Builders that help make writing equals(), hashCode, and toString() much simpler.

To quote the project's homepage:

The standard Java libraries fail to provide enough methods for manipulation of its core classes. The Lang Component provides these extra methods.

Here's a simple object with two properties that demonstrates how to use some of the Builders:

import org.apache.commons.lang.builder.EqualsBuilder;
import org.apache.commons.lang.builder.HashCodeBuilder;
import org.apache.commons.lang.builder.ToStringBuilder;

public class Person {

    String name;   
    Integer age;

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

    @Override
    public boolean equals(Object object) {
        return EqualsBuilder.reflectionEquals(this, object);
    }

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

    @Override
    public String toString() {
        return ToStringBuilder.reflectionToString(this);
    }
}

An example use of the overriden methods in Groovy:

    def person = new Person("Costanza", 35)
    println "String: $person"
    println "Hash Code: " + person.hashCode()

    def samePerson = new Person("Costanza", 35)
    def differentPerson = new Person("Newman", 35)
    println "Same equals(): " + person.equals(samePerson)
    println "Different equals(): " + person.equals(differentPerson)

Produces:

    String: Person@6bb36[name=Costanza,age=35]
    Hash Code: -422159695
    Same equals(): true
    Different equals(): false

An alternative to ToStringBuilder is ReflectionToStringBuilder:

    import org.apache.commons.lang.builder.ReflectionToStringBuilder;
    ...
    public String toString() {
       return ReflectionToStringBuilder.toString(this);
    }

For String building, there are also various styles you can pass to the builder's constructor: String Styles.

There's also a CompareToBuilder that I have yet to play with.