override equals method to compare more than one field in java

Question

What is the best way to override equals method in java to compare more than one field? For example, I have 4 objects in the class, o1, o2, o3, o4 and I want compare all of t

Answer 1

One thing is to have a helper method in a utility class:

public static boolean equals(Object o1, Object o2)
{
     if (o1 == o2)
     {
         return true;
     }
     if (o1 == null || o2 == null)
     {
         return false;
     }
     return o1.equals(o2);
}

Then you can write:

public boolean equals(Object other)
{
    if (other == null || this.getClass() != other.getClass())
    {
        return false;
    }
    Foo x = (Foo) other;
    return Helper.equals(o1, x.o1) &&
           Helper.equals(o2, x.o2) &&
           Helper.equals(o3, x.o3) &&
           Helper.equals(o4, x.o4);
}

Note that this way it also copes when two fields are both null, which the code in the question doesn't. (I say "copes" - it gives a result which is more consistent with the rest of Java.)

You can create a similar helper method for hashCode too.

Note that Guava already supports this in its Objects class (and I'm sure many other utility libraries do too).