Getting NullPointerException While trying to implement EqualsVerifier

[Haroen Viaene]

Hey,

First of all, thanks for your project, it's a great idea and looks like it will make my life easier.

However I had a bit of trouble implementing it. 

As you can see in this PR https://github.com/gin-fizz/pollistics/pull/11, the tests still fail 

EqualsVerifier.forClass(User.class)

  .withPrefabValues(Poll.class, new Poll(), new Poll())

  .usingGetClass()

  .verify();

When not covering it in a try/catch block I get 

com.pollistics.models.UserTest > equalsContract FAILED

    java.lang.NullPointerException

        at com.pollistics.models.Poll.equals(Poll.java:74)

        at nl.jqno.equalsverifier.EqualsVerifier.withPrefabValues(EqualsVerifier.java:198)

        at com.pollistics.models.UserTest.equalsContract(UserTest.java:30)

The equals check looks pretty normal I think, except that the classes use each other. 

@Override

public boolean equals(Object obj) {

  if(this == obj)

    return true;

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

    return false;

  User user = (User) obj;

  return this.getId().equals(user.getId());

}

Thanks for your answer 😊

[Haroen Viaene]

I'm now noticing that the problem is at my own, because I didn't initialise the id

[Jan Ouwens]

Hi Haroen,

Sorry I wasn't able to reply sooner.

You're right, the issue is that the id is undefined. Unfortunately, setting it in the constructor won't help, because EqualsVerifier bypasses it.

There are two ways you can make the EqualsVerifier test pass. Either you can add a null check in the equals method:

    return this.getId() == null ? user.getId() == null : this.getId().equals(user.getId());

(Or simply use Objects.equals(this.getId(), user.getId()) )

Or, you can add a line to your call to EqualsVerifier:

    EqualsVerifier.forClass(User.class)

      .withPrefabValues(Poll.class, new Poll(), new Poll())

      .usingGetClass()

      .suppress(Warning.NULL_FIELDS)

      .verify();

The first approach is correct if id is allowed to be null (because if something can be null, you have to check for it). The second approach is correct if id is never allowed to be null.

Good luck!

Jan

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