The Object#equals(Object obj) method is used to compare two objects to see if they are equal.
The obj parameter’s type is Object, this means that an object of any type can be passed as a parameter to this
method.
Any class overriding Object#equals(Object obj) should respect this contract, accept any object as an argument, and return
false when the argument’s type differs from the expected type. The obj parameter’s type can be checked using
instanceof or by comparing the getClass() value:
@Override
public boolean equals(Object obj) {
// ...
if (this.getClass() != obj.getClass()) {
return false;
}
// ...
}
However, it is an issue to assume that the equals method will only be used to compare objects of the same type. Casting the
obj parameter without a prior test will throw a ClassCastException instead of returning false.
public class MyClass {
@Override
public boolean equals(Object obj) {
MyClass that = (MyClass) obj; // may throw a ClassCastException
// ...
}
// ...
}
This rule raises an issue when obj parameter’s type has not been tested before a cast operation.
