# V6134\. It is not recommended to throw exceptions from the 'equals' method\.

The analyzer has detected that an exception is explicitly thrown in the equals method\. This behavior is not recommended as this method may be used in contexts where throwing an exception is not expected\. This can occur both in the user's code and when interacting with the standard library\. 

The example: 

```cpp
class User {
  ....
  @Override
  public boolean equals(Object o) {
    if (o == null) {
      throw new IllegalArgumentException("....");
    }
    ....
  }
}
```

According to its [contract](https://docs.oracle.com/en/java/javase/25/docs/api/java.base/java/lang/Object.html#equals(java.lang.Object)), the [`Object.equals`](https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html#equals-java.lang.Object-) method returns `false` if `null` is passed as an argument\. However, in this overridden method, an [`IllegalArgumentException`](https://docs.oracle.com/javase/8/docs/api/java/lang/IllegalArgumentException.html) is thrown instead\. This can lead to issues when the object is used in a collection\.

The example:

```cpp
List<User> users = new ArrayList<>();
users.add(null);
users.add(new User("a@example.com"));
//....
users.contains(new User("b@example.com")); // IllegalArgumentException
```

The `ArrayList.contains` method uses `equals` to compare the passed argument with the elements of the collection\. Since the collection contains an object that references `null`, passing this object to the `equals` method results in the `IllegalArgumentException`\.

To avoid such issues, return the appropriate `boolean` value instead of throwing an exception\.

The fixed example:

```cpp
@Override
public boolean equals(Object o) {
  if (o == null) {
    return false;
  }
  ....
}
```