`equals` method inherits parent class implementation instead of overriding `Object.equals`JAVA-E0099

This class defines an equals method that doesn't override Object.equals(Object). In addition, it inherits an overridden equals(Object) method from a superclass. This may lead to unexpected results when comparing instances of this class.

Bad Practice

class Parent {

String id;

@Override
public boolean equals(Object other) { return other instanceOf Parent && this.id.equals(((Parent)other).id); }

}

class Child extends Parent {

String name;

public boolean equals(Child other) {
    return this.name == other.name && this.id == other.id;
}

}

Here, Child inherits an overridden definition of equals from Parent and also defines an overloaded version of equals taking a Child as an argument. Any standard library collection of Child will use Parent's definition of equals instead of the intended overloaded version in Child, ignoring the name field completely.

Recommended

It is recommended to explicitly override the default equals(Object) method to make things clear, and also prevent any subtle logic bugs if equals is required to behave differently in the child class.

By not doing so, equality checks for this class may no longer be symmetric or transitive.

public boolean equals(Child other) {
    return this.name == other.name && this.id == other.id;
}

public boolean equals(Object other) {
    if (other instanceof Child) return this.equals((Child)other);
    else // ...
}

References

• SpotBugs - EQ_OTHER_NO_OBJECT