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

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

CodePudding user 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.

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.

CodePudding user response：

You are not using a best practice. Change your equals to be something like the following (null check first, then same check, then class check):

 public boolean equals(Object obj) {
   if (obj == null) { return false; }
   if (obj == this) { return true; }
   if (obj.getClass() != getClass()) {
     return false;
   }
   
   ... do the actual comparison here
 }

Note: the code above is a paraphrase of Apache EqualsBuilder

CodePudding user response：

I use this standard equals and hashcode implementations for JPA entities (as described here):

@Override
public boolean equals(Object o) {
    if (this == o) {
        return true;
    }
    if (!(o instanceof MyClass)) {
        return false;
    }
    MyClass other = (MyClass) o;
    return id != null && id.equals(other.getId());
}


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