Project Lombok - toString(), equals() and hashCode() Method Example


In this post, I will show you how to generate the toString(), equals() and hashCode() automatically in Java projects using Project Lombok annotations - @ToString, @EqualsAndHashCode.
Project Lombok is a very useful tool for Java projects to reduce boiler-plate code so in this example I will demonstrate how to automatically generate toString(), equals() and hashCode() automatically in Java projects using Project Lombok.

Project Lombok Maven

Create a simple maven project using - How to Create a Simple Maven Project in Eclipse article.
Add the below dependency in your maven project pom.xml file:
<!-- https://mvnrepository.com/artifact/org.projectlombok/lombok -->
<dependency>
    <groupId>org.projectlombok</groupId>
    <artifactId>lombok</artifactId>
    <version>1.18.4</version>
    <scope>provided</scope>
</dependency>

Adding the Lombok Plugin in IDE (Eclipse)

Follow below steps to install Lombok in eclipse for Windows:
  • Downloaded jar from https://projectlombok.org/download or use the jar which is downloaded from your maven build.
  • Execute command in terminal: java -jar lombok.jar
  • This command will open window as shown in the picture below, install and quit the installer and restart eclipse.

Without Project Lombok

Let's first look at a sample of code which has a boilerplate code. Let's create a User class with toString(), equals() and hashCode() methods:
package net.javaguides.lombok;

import java.time.LocalDate;

/**
 * 
 * @author Ramesh Fadatare
 *
 */
public class User {
    private long id;
    private String firstName;
    private String lastName;
    private int age;
    private LocalDate createdDate;
    private LocalDate updatedDate;
    private String gender;

    public long getId() {
        return id;
    }
    public String getFirstName() {
        return firstName;
    }
    public String getLastName() {
        return lastName;
    }
    public int getAge() {
        return age;
    }
    public LocalDate getCreatedDate() {
        return createdDate;
    }
    public LocalDate getUpdatedDate() {
        return updatedDate;
    }
    public String getGender() {
        return gender;
    }
    public void setId(long id) {
        this.id = id;
    }
    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }
    public void setLastName(String lastName) {
        this.lastName = lastName;
    }
    public void setAge(int age) {
        this.age = age;
    }
    public void setCreatedDate(LocalDate createdDate) {
        this.createdDate = createdDate;
    }
    public void setUpdatedDate(LocalDate updatedDate) {
        this.updatedDate = updatedDate;
    }
    public void setGender(String gender) {
        this.gender = gender;
    }


    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + age;
        result = prime * result + ((createdDate == null) ? 0 : createdDate.hashCode());
        result = prime * result + ((firstName == null) ? 0 : firstName.hashCode());
        result = prime * result + ((gender == null) ? 0 : gender.hashCode());
        result = prime * result + (int)(id ^ (id >>> 32));
        result = prime * result + ((lastName == null) ? 0 : lastName.hashCode());
        result = prime * result + ((updatedDate == null) ? 0 : updatedDate.hashCode());
        return result;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        User other = (User) obj;
        if (age != other.age)
            return false;
        if (createdDate == null) {
            if (other.createdDate != null)
                return false;
        } else if (!createdDate.equals(other.createdDate))
            return false;
        if (firstName == null) {
            if (other.firstName != null)
                return false;
        } else if (!firstName.equals(other.firstName))
            return false;
        if (gender == null) {
            if (other.gender != null)
                return false;
        } else if (!gender.equals(other.gender))
            return false;
        if (id != other.id)
            return false;
        if (lastName == null) {
            if (other.lastName != null)
                return false;
        } else if (!lastName.equals(other.lastName))
            return false;
        if (updatedDate == null) {
            if (other.updatedDate != null)
                return false;
        } else if (!updatedDate.equals(other.updatedDate))
            return false;
        return true;
    }
    @Override
    public String toString() {
        return "User [id=" + id + ", firstName=" + firstName + ", lastName=" + lastName + ", age=" + age +
            ", createdDate=" + createdDate + ", updatedDate=" + updatedDate + ", gender=" + gender + "]";
    }
}
Note that we have also generated getter and setter methods for User class properties.

With Project Lombok

Let's eliminate boilerplate code using Lombok @ToString, @EqualsAndHashCode annotations:
package net.javaguides.lombok.equalshashcode;

import java.time.LocalDate;

import lombok.EqualsAndHashCode;
import lombok.Getter;
import lombok.Setter;
import lombok.ToString;

@Getter
@Setter
@ToString
@EqualsAndHashCode
public class UserLombokModel {
    private long id;
    private String firstName;
    private String lastName;
    private int age;
    private LocalDate createdDate;
    private LocalDate updatedDate;
    private String gender;

}

Testing

As you installed Lombok plugin in eclipse so we can test using a main() method to check whether equals(), hashCode(), and toString() methods generated properly or not:
package net.javaguides.lombok.equalshashcode;

import java.time.LocalDate;

public class LombokTest {
    public static void main(String[] args) {
        UserLombokModel lombokModel = new UserLombokModel();

        lombokModel.setId(100 L);
        lombokModel.setFirstName("Ramesh");
        lombokModel.setLastName("Fadatare");
        lombokModel.setAge(28);
        lombokModel.setGender("Male");
        lombokModel.setCreatedDate(LocalDate.now());
        lombokModel.setUpdatedDate(LocalDate.now());

        UserLombokModel lombokModel2 = new UserLombokModel();

        lombokModel2.setId(100 L);
        lombokModel2.setFirstName("Ramesh");
        lombokModel2.setLastName("Fadatare");
        lombokModel2.setAge(28);
        lombokModel2.setGender("Male");
        lombokModel2.setCreatedDate(LocalDate.now());
        lombokModel2.setUpdatedDate(LocalDate.now());

        // equals method
        System.out.println(lombokModel.equals(lombokModel2));

        // hashCode method
        System.out.println(lombokModel.hashCode());
        System.out.println(lombokModel2.hashCode());

        // toString method
        System.out.println(lombokModel.toString());
    }
}
Output:

Exclude Fields

We can also exclude some fields which we don’t want to include in toString(), equals() and hashCode() method by declaring exclude attribute in @ToString and @EqualsAndHashCode annotation.
For example, below is the code to exclude createdDate property in the User class:
package net.javaguides.lombok.equalshashcode;

import java.time.LocalDate;

import lombok.EqualsAndHashCode;
import lombok.Getter;
import lombok.Setter;
import lombok.ToString;

@Getter
@Setter
@ToString(exclude = "createdDate")
@EqualsAndHashCode(exclude = "createdDate")
public class UserLombokModel {
    private long id;
    private String firstName;
    private String lastName;
    private int age;
    private LocalDate createdDate;
    private LocalDate updatedDate;
    private String gender;

}
Now, if you check the .class file of above User.class, the content of User.class will be as below:
package net.javaguides.lombok.equalshashcode;

import java.time.LocalDate;

public class UserLombokModel {
    private long id;
    private String firstName;
    private String lastName;
    private int age;
    private LocalDate createdDate;
    private LocalDate updatedDate;
    private String gender;

    public void setId(long id) {
        this.id = id;
    }

    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public void setCreatedDate(LocalDate createdDate) {
        this.createdDate = createdDate;
    }

    public void setUpdatedDate(LocalDate updatedDate) {
        this.updatedDate = updatedDate;
    }

    public void setGender(String gender) {
        this.gender = gender;
    }

    public String toString() {
        return "UserLombokModel(id=" + getId() + ", firstName=" + getFirstName() + ", lastName=" + getLastName() + ", age=" + getAge() + ", updatedDate=" + getUpdatedDate() + ", gender=" + getGender() + ")";
    }

    public boolean equals(Object o) {
        if (o == this) {
            return true;
        }
        if (!(o instanceof UserLombokModel)) {
            return false;
        }
        UserLombokModel other = (UserLombokModel) o;
        if (!other.canEqual(this)) {
            return false;
        }
        if (getId() != other.getId()) {
            return false;
        }
        Object this$firstName = getFirstName();
        Object other$firstName = other.getFirstName();
        if (this$firstName == null ? other$firstName != null : !this$firstName.equals(other$firstName)) {
            return false;
        }
        Object this$lastName = getLastName();
        Object other$lastName = other.getLastName();
        if (this$lastName == null ? other$lastName != null : !this$lastName.equals(other$lastName)) {
            return false;
        }
        if (getAge() != other.getAge()) {
            return false;
        }
        Object this$updatedDate = getUpdatedDate();
        Object other$updatedDate = other.getUpdatedDate();
        if (this$updatedDate == null ? other$updatedDate != null : !this$updatedDate.equals(other$updatedDate)) {
            return false;
        }
        Object this$gender = getGender();
        Object other$gender = other.getGender();
        return this$gender == null ? other$gender == null : this$gender.equals(other$gender);
    }

    protected boolean canEqual(Object other) {
        return other instanceof UserLombokModel;
    }

    public int hashCode() {
        int PRIME = 59;
        int result = 1;
        long $id = getId();
        result = result * 59 + (int)($id >>> 32 ^ $id);
        Object $firstName = getFirstName();
        result = result * 59 + ($firstName == null ? 43 : $firstName.hashCode());
        Object $lastName = getLastName();
        result = result * 59 + ($lastName == null ? 43 : $lastName.hashCode());
        result = result * 59 + getAge();
        Object $updatedDate = getUpdatedDate();
        result = result * 59 + ($updatedDate == null ? 43 : $updatedDate.hashCode());
        Object $gender = getGender();
        result = result * 59 + ($gender == null ? 43 : $gender.hashCode());
        return result;
    }

    public long getId() {
        return this.id;
    }

    public String getFirstName() {
        return this.firstName;
    }

    public String getLastName() {
        return this.lastName;
    }

    public int getAge() {
        return this.age;
    }

    public LocalDate getCreatedDate() {
        return this.createdDate;
    }

    public LocalDate getUpdatedDate() {
        return this.updatedDate;
    }

    public String getGender() {
        return this.gender;
    }
}

Reference

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