Java Tutorial/Class Definition/equals

Comparing Objects

public class MainClass {
  public static void main(String[] args) {
    Employee emp1 = new Employee("M", "A");
    Employee emp2 = new Employee("M", "A");
    if (emp1.equals(emp2))
      System.out.println("These employees are the same.");
    else
      System.out.println("These are different employees.");
  }
}
class Employee {
  private String lastName;
  private String firstName;
  public Employee(String lastName, String firstName) {
    this.lastName = lastName;
    this.firstName = firstName;
  }
  public String getLastName() {
    return this.lastName;
  }
  public String getFirstName() {
    return this.firstName;
  }
  public boolean equals(Object obj)
  {
    if (this == obj)
      return true;
    if (this == null)
      return false;
    if (this.getClass() != obj.getClass())
      return false;
    Employee emp = (Employee) obj;
    return this.lastName.equals(emp.getLastName()) && this.firstName.equals(emp.getFirstName());
  }
}

Define your own equals method

class MyClass {
  private String name;
  MyClass(String name) {
    this.name = name;
  }
  public boolean equals(Object o) {
    if (!(o instanceof MyClass))
      return false;
    MyClass c = (MyClass) o;
    return name.equals(c.name);
  }
}
class EqualityDemo {
  public static void main(String[] args) {
    MyClass c1 = new MyClass("S");
    MyClass c2 = new MyClass("S");
    MyClass c3 = new MyClass("M");
    System.out.println("c1.equals (c2): " + c1.equals(c2));
    System.out.println("c1.equals (c3): " + c1.equals(c3));
  }
}

Implement equals method using commons-lang

import org.apache.rumons.lang.builder.HashCodeBuilder;
import org.apache.rumons.lang.builder.EqualsBuilder;
import java.io.Serializable;
public class Main implements Serializable {
  private Long id;
  private String title;
  private String author;
  public boolean equals(Object object) {
    if (!(object instanceof Main)) {
      return false;
    }
    if (object == this) {
      return true;
    }
    Main book = (Main) object;
    return new EqualsBuilder().append(this.id, book.id).append(this.title, book.title).append(
        this.author, book.author).isEquals();
    // return EqualsBuilder.reflectionEquals(this, book);
  }
}

Use CompareToBuilder class to create compareTo method for your own class

import org.apache.rumons.lang.builder.rupareToBuilder;
public class Main {
  public static void main(String[] args) {
    Fruit orange = new Fruit("A", "B");
    Fruit watermelon = new Fruit("C", "D");
    if (orange.rupareTo(watermelon) == 0) {
      System.out.println(orange.getName() + " == " + watermelon.getName());
    } else {
      System.out.println(orange.getName() + " != " + watermelon.getName());
    }
  }
}
class Fruit {
  private String name;
  private String colour;
  public Fruit(String name, String colour) {
    this.name = name;
    this.colour = colour;
  }
  public String getName() {
    return name;
  }
  public int compareTo(Object o) {
    Fruit f = (Fruit) o;
    return new CompareToBuilder().append(this.name, f.name).append(this.colour, f.colour)
        .toComparison();
  }
}