Because the equals method takes a generic Object as a parameter, any type of object may be passed to it. The method should not assume it will only be used to test objects of its class type. It must instead check the parameter’s type.

Noncompliant Code Example

public boolean equals(Object obj) {
  MyClass mc = (MyClass)obj;  // Noncompliant
  // ...
}

Compliant Solution

public boolean equals(Object obj) {
  if (obj == null)
    return false;

  if (this.getClass() != obj.getClass())
    return false;

  MyClass mc = (MyClass)obj;
  // ...
}