Java @Override equals(): When this.getClass() != o.getClass() fails but shouldn't

Question

I have this @Override for equals() in my MyClass class:

@Entity( name = "MyClass" )
@Table( name = "my_class" )
public class MyClass extends MySuperClass
{
  ...
  @Override
  public boolean equals( Object o )
  {
    if ( this == o )
    {
      return true;
    }
    if ( o == null || this.getClass() != o.getClass() )
    {
      return false;
    }
    if ( !super.equals( o ) )
    {
      return false;
    }
    MyClass that = ( MyClass ) o;
    return this.var1.equals( that.var1 ) && this.var2.equals( that.var2 );
  }
  ...
}

Pretty standard. Matter of fact, it follows Java best practices.
Later in life I have this in another sub-package class (my controller class):

...
package com.a.b.api.controllers;
...
import com.a.b.jpa.models.MyClass;
...
MyClass myObject1 = new MyClass( var1, var2 );
MyClass myObject2 = this.myClassRepository.getById( 1 ); // SpringBoot/Jpa/Hibernate

if ( myObject2.equals( myObject1 ) )
{
   ...do something...
}
...
this.myClassRepository.save( myObject1 );
...

My problem is that the .equals() is always failing here:

if ( o == null || this.getClass() != o.getClass() )

because java says that this.getClass() and o.getClass() are NOT equal. When I debug the code (in Intellij IDEA 2022.1 UE) I see this:

this.getClass() = MyClass@13706

but

o.getClass = com.a.b.jpa.models.MyClass@8f7462

But they are the same class! Almost every Java book, tutorial, blog, Intellij IDEA, etc. demonstrates the .equals() this way. I have tried this in Ubuntu 20.04.4 LTS java-14-openjdk-amd64 and java-17-openjdk-amd64 with the same results.

What am I doing wrong?

Answer 1

myObject2 is an instance of a proxy class, generated at runtime by Hibernate using Byte Buddy. The generated proxy intercepts all method invocations, that's why getClass() returns different results.

As an alternative to getClass(), using instanceof might be another approach:

if ( !(this instanceof MyClass && o instanceof MyClass) )
{
   return false;
}

However keep in mind that instanceof has its drawbacks. It violates the symmetry principle.

You shouldn't compare these objects in the first place, since a new object should be different from a Hibernate managed one that has a persistent state.

Answer 2

happy songs correctly stated in his response:

myObject2 is an instance of a proxy class, generated at runtime by Hibernate using Byte Buddy. The generated proxy intercepts all method invocations, that's why getClass() returns different results.

I really didn't want to use instanceof because that is considered bad practice so I started poking around and stumbled onto a post having a similar issue. Their solution was to add the final keyword to their class declaration. I thought this insignificant but gave it try - AND IT WORKED! Adding the final keyword caused

if ( o == null || this.getClass() != o.getClass() )

and

if ( o == null || !this.getClass().equals( o.getClass() ) )

to work properly. My class code is now:

@Entity( name = "MyClass" )
@Table( name = "my_class" )
final public class MyClass extends MySuperClass
{
  ...
  @Override
  public boolean equals( Object o )
  {
    if ( this == o )
    {
      return true;
    }
    if ( o == null || !this.getClass().equals( o.getClass() ) )
    {
      return false;
    }
    if ( !super.equals( o ) )
    {
      return false;
    }
    MyClass that = ( MyClass ) o;
    return this.var1.equals( that.var1 ) && this.var2.equals( that.var2 );
  }
  ...
}

Thank you all for your assistance! And a big thank you to happy songs for pointing me in the proper direction!