Java override Object equals() method

Question

How do I override the equals method in the object class?

i.e I have

class Person{

//need to override here
public boolean equals (Object obj){

}


        

Answer 1

It's actually more complicated than you might think. Have Eclipse (or whatever IDE you're using) auto-generate an equals method; you'll see it contains a few checks and casts before it does a comparison.

Also see here: http://www.javapractices.com/topic/TopicAction.do?Id=17

Answer 2

I know this is answered, but in my travels I have found this the most efficient way to override the comparison of an object to make sure it happens the same globally:

@Override
public boolean equals(Object o) {
    return o instanceof Person && this.getSomeMagicalField().equals(((Person) o).getSomeMagicalField());
}

or if you are not comparing strings:

@Override
public boolean equals(Object o) {
    return o instanceof Person && this.getSomeMagicalField() == (Person) o).getSomeMagicalField();
}

Answer 3

@Override
public boolean equals(Object o) 
{
    if (o instanceof Person) 
    {
      Person c = (Person) o;
      if ( this.FIELD.equals(c.FIELD) ) //whatever here
         return true;
    }
    return false;
}

Answer 4

Take a look at Regarding Object Comparison.

Be aware that if you override equals() you must also override hashCode(). The equals/hashCode contract is that if two objects are equal they must have the same hash code.

Answer 5

If you plan to create subclasses of Person, use something like

if(obj!=null && obj.getClass() == Person.class)

rather than instanceof

Answer 6

One more point may be good to know that after you override equals() method (and also hashcode()) method you can to compare two objects of same class like follows:

Person p1 = new Person();
Person p2 = new Person();

....

if ( p1.equals( p2 ) )

{
   // --- Two Persons are equal, w.r.t the fields you specified in equals method ---

}