Why doesn't the Java Vector's contains() method seem to call my custom equals() method?

Vector.contains() will call a method called Object.equals(Object) on your elements. Your method CustomObject.equals(CustomObject) does not override equals(Object), rather it overloads the 1-argument equals method signature. As such, it will not be called by any caller that is expecting to call an implementation of Object.equals(Object). You need to rewrite the method as an override. So: boolean equals(Object b) { return b instanceof CustomObject && name.trim().equalsIgnoreCase(((CustomObject )b).name.trim()) ); } Note also the use of the primitive boolean type as the return type - the return type of an overriding method must be a strict subclass of the return type of the overridden method and Boolean is not a strict subclass of boolean (since primitive types cannot be subclassed).